Long-range atmospheric transport and deposition of anthropogenically-sourced aerosol iron (Fe) affects surface ocean biogeochemistry far from the emission source. However, it is challenging to establish the integrated impact of anthropogenic aerosol Fe on surface ocean dissolved Fe (dFe) cycling, due to other Fe sources and in situ cycling processes. Previous work has used a distinctively-light Fe isotopic signature (δ56Fe) associated with anthropogenic activity to track the contribution of anthropogenic Fe at the basin scale. However, this requires not only the determination of the δ56Fe endmember of all potential Fe sources, but also the assessment of how upper ocean biogeochemical cycling modulates surface ocean dFe signatures (δ56Fediss). Here we accounted for dust, fire and anthropogenic Fe deposition fields in a global ocean biogeochemical model with an integrated δ56Fecycle to quantify the impact of anthropogenic Fe on surface ocean Fe and δ56Fe, with a focus on the North Pacific. The effect of anthropogenic Fe is spatially distinct and seasonally variable in our model, depending on the biogeochemical state of the upper ocean. In the subtropical regions where Fe is not limiting, anthropogenic Fe input leads to increased dFe levels and, at times, phytoplankton Fe uptake. δ56Fediss declines due to the very light anthropogenic δ56Fe endmember, most prominently in low dFe areas of the subtropical North Pacific gyre. In Fe-limited systems, such as the subpolar gyre, anthropogenic Fe stimulates both primary production and Fe uptake with little change to summertime dFe levels. Moreover, the decrease in δ56Fediss is amplified as extra Fe dampens the impact of the fractionation effects associated with Fe uptake and complexation, whereby the overall δ56Fediss often remains positive. Overall, it is important to account for biological parameters, such as primary productivity or Fe limitation, when assessing the oceanic impact of anthropogenic Fe.
}, publisher={Copernicus GmbH}, author={König, Daniela and Conway, Tim and Hamilton, Douglas and Tagliabue, Alessandro}, year={2022}, month={Mar} } @article{liu_matsui_hamilton_lamb_rathod_schwarz_mahowald_2022, title={The underappreciated role of anthropogenic sources in atmospheric soluble iron flux to the Southern Ocean}, volume={5}, url={https://doi.org/10.1038/s41612-022-00250-w}, DOI={10.1038/s41612-022-00250-w}, abstractNote={Abstract The atmospheric deposition of soluble (bioaccessible) iron enhances ocean primary productivity and subsequent atmospheric CO 2 sequestration in iron-limited ocean basins, especially the Southern Ocean. While anthropogenic sources have been recently suggested to be important in some northern hemisphere oceans, the role in the Southern Ocean remains ambiguous. By comparing multiple model simulations with the new aircraft observations for anthropogenic iron, we show that anthropogenic soluble iron deposition flux to the Southern Ocean could be underestimated by more than a factor of ten in previous modeling estimates. Our improved estimate for the anthropogenic iron budget enhances its contribution on the soluble iron deposition in the Southern Ocean from about 10% to 60%, implying a dominant role of anthropogenic sources. We predict that anthropogenic soluble iron deposition in the Southern Ocean is reduced substantially (30‒90%) by the year 2100, and plays a major role in the future evolution of atmospheric soluble iron inputs to the Southern Ocean.}, number={1}, journal={npj Climate and Atmospheric Science}, publisher={Springer Science and Business Media LLC}, author={Liu, Mingxu and Matsui, Hitoshi and Hamilton, Douglas S. and Lamb, Kara D. and Rathod, Sagar D. and Schwarz, Joshua P. and Mahowald, Natalie M.}, year={2022}, month={Dec} } @article{wiseman_moore_twining_hamilton_mahowald_2022, title={Variable Phytoplankton Iron Quotas Modify Marine Biogeochemistry and Dampen the Response to Varying Atmospheric Iron Deposition}, url={https://doi.org/10.1002/essoar.10511628.1}, DOI={10.1002/essoar.10511628.1}, author={Wiseman, Nicola A and Moore, Jefferson Keith and Twining, Benjamin S. and Hamilton, Douglas Stephen and Mahowald, Natalie M}, year={2022}, month={Jun} } @article{ardyna_hamilton_harmel_lacour_bernstein_laliberte_horvat_laxenaire_mills_dijken_et al._2022, title={Wildfire aerosol deposition likely amplified a summertime Arctic phytoplankton bloom}, volume={3}, ISSN={["2662-4435"]}, url={https://doi.org/10.1038/s43247-022-00511-9}, DOI={10.1038/s43247-022-00511-9}, abstractNote={Abstract Summertime wildfire activity is increasing in boreal forest and tundra ecosystems in the Northern Hemisphere. However, the impact of long range transport and deposition of wildfire aerosols on biogeochemical cycles in the Arctic Ocean is unknown. Here, we use satellite-based ocean color data, atmospheric modeling and back trajectory analysis to investigate the transport and fate of aerosols emitted from Siberian wildfires in summer 2014 and their potential impact on phytoplankton dynamics in the Arctic Ocean. We detect large phytoplankton blooms near the North Pole (up to 82°N in the eastern Eurasian Basin). Our analysis indicates that these blooms were induced by the northward plume transport and deposition of nutrient-bearing wildfire aerosols. We estimate that these highly stratified surface waters received large amounts of wildfire-derived nitrogen, which alleviated nutrient stress in the phytoplankton community and triggered an unusually large bloom event. Our findings suggest that changes in wildfire activity may strongly influence summertime productivity in the Arctic Ocean.}, number={1}, journal={COMMUNICATIONS EARTH & ENVIRONMENT}, author={Ardyna, Mathieu and Hamilton, Douglas S. and Harmel, Tristan and Lacour, Leo and Bernstein, Diana N. and Laliberte, Julien and Horvat, Christopher and Laxenaire, Remi and Mills, Matthew M. and Dijken, Gert and et al.}, year={2022}, month={Sep} } @article{kok_adebiyi_albani_balkanski_checa-garcia_chin_colarco_hamilton_huang_ito_et al._2021, title={Contribution of the world's main dust source regions to the global cycle of desert dust}, volume={1}, url={https://doi.org/10.5194/acp-2021-4}, DOI={10.5194/acp-2021-4}, abstractNote={Abstract. Even though desert dust is the most abundant aerosol by mass in Earth's atmosphere, the relative contributions of the world’s major dust source regions to the global dust cycle remain poorly constrained. This problem hinders accounting for the potentially large impact of regional differences in dust properties on clouds, the Earth's energy balance, and terrestrial and marine biogeochemical cycles. Here, we constrain the contribution of each of the world’s main dust source regions to the global dust cycle. We use an analytical framework that integrates an ensemble of global model simulations with observationally informed constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth. We obtain a data set that constrains the relative contribution of each of nine major source regions to size-resolved dust emission, atmospheric loading, optical depth, concentration, and deposition flux. We find that the 22–29 Tg (one standard error range) global loading of dust with geometric diameter up to 20 μm is partitioned as follows: North African source regions contribute ~50 % (11–15 Tg), Asian source regions contribute ~40 % (8–13 Tg), and North American and Southern Hemisphere regions contribute ~10 % (1.8–3.2 Tg). Current models might on average be overestimating the contribution of North African sources to atmospheric dust loading at ~65 %, while underestimating the contribution of Asian dust at ~30 %. However, both our results and current models could be affected by unquantified biases, such as due to errors in separating dust aerosol optical depth from that produced by other aerosol species in remote sensing retrievals in poorly observed desert regions. Our results further show that each source region's dust loading peaks in local spring and summer, which is partially driven by increased dust lifetime in those seasons. We also quantify the dust deposition flux to the Amazon rainforest to be ~10 Tg/year, which is a factor of 2–3 less than inferred from satellite data by previous work that likely overestimated dust deposition by underestimating the dust mass extinction efficiency. The data obtained in this paper can be used to obtain improved constraints on dust impacts on clouds, climate, biogeochemical cycles, and other parts of the Earth system.}, publisher={Copernicus GmbH}, author={Kok, Jasper F. and Adebiyi, Adeyemi A. and Albani, Samuel and Balkanski, Yves and Checa-Garcia, Ramiro and Chin, Mian and Colarco, Peter R. and Hamilton, Douglas S. and Huang, Yue and Ito, Akinori and et al.}, year={2021}, month={Jan} } @article{kok_adebiyi_albani_balkanski_checa-garcia_chin_colarco_hamilton_huang_ito_et al._2021, title={Contribution of the world's main dust source regions to the global cycle of desert dust}, volume={21}, url={https://doi.org/10.5194/acp-21-8169-2021}, DOI={10.5194/acp-21-8169-2021}, abstractNote={Abstract. Even though desert dust is the most abundant aerosol by mass in Earth's atmosphere, the relative contributions of the world's major source regions to the global dust cycle remain poorly constrained. This problem hinders accounting for the potentially large impact of regional differences in dust properties on clouds, the Earth's energy balance, and terrestrial and marine biogeochemical cycles. Here, we constrain the contribution of each of the world's main dust source regions to the global dust cycle. We use an analytical framework that integrates an ensemble of global aerosol model simulations with observationally informed constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth (DAOD). We obtain a dataset that constrains the relative contribution of nine major source regions to size-resolved dust emission, atmospheric loading, DAOD, concentration, and deposition flux. We find that the 22–29 Tg (1 standard error range) global loading of dust with a geometric diameter up to 20 µm is partitioned as follows: North African source regions contribute ∼ 50 % (11–15 Tg), Asian source regions contribute ∼ 40 % (8–13 Tg), and North American and Southern Hemisphere regions contribute ∼ 10 % (1.8–3.2 Tg). These results suggest that current models on average overestimate the contribution of North African sources to atmospheric dust loading at ∼ 65 %, while underestimating the contribution of Asian dust at ∼ 30 %. Our results further show that each source region's dust loading peaks in local spring and summer, which is partially driven by increased dust lifetime in those seasons. We also quantify the dust deposition flux to the Amazon rainforest to be ∼ 10 Tg yr−1, which is a factor of 2–3 less than inferred from satellite data by previous work that likely overestimated dust deposition by underestimating the dust mass extinction efficiency. The data obtained in this paper can be used to obtain improved constraints on dust impacts on clouds, climate, biogeochemical cycles, and other parts of the Earth system.}, number={10}, journal={Atmospheric Chemistry and Physics}, publisher={Copernicus GmbH}, author={Kok, Jasper F. and Adebiyi, Adeyemi A. and Albani, Samuel and Balkanski, Yves and Checa-Garcia, Ramiro and Chin, Mian and Colarco, Peter R. and Hamilton, Douglas S. and Huang, Yue and Ito, Akinori and et al.}, year={2021}, month={May}, pages={8169–8193} } @article{wan_hamilton_mahowald_2021, title={Importance of Uncertainties in the Spatial Distribution of Preindustrial Wildfires for Estimating Aerosol Radiative Forcing}, volume={48}, url={https://doi.org/10.1029/2020GL089758}, DOI={10.1029/2020GL089758}, abstractNote={Uncertainty in preindustrial aerosol emissions, including fires, is one of the largest sources of uncertainty in estimating anthropogenic radiative forcing. Here, we quantify the range in aerosol forcing associated with uncertainty in the location and magnitude of preindustrial fire emissions in a climate model based on four emission estimates. With varied emission location and magnitude among the fire estimates, we find the change in aerosol forcing from present-day to preindustrial is between −0.4 and 0.3 W/m2 for direct radiative forcing and between −1.8 and 0.6 W/m2 for cloud albedo forcing. Altering only the spatial distribution of preindustrial fires for a fixed magnitude adds a previously unaccounted 25% uncertainty to the total aerosol radiative forcing range. Future studies must account for the uncertainty in the spatial distribution of fire and other aerosol emissions as regional differences contribute substantial additional uncertainty to anthropogenic radiative forcing estimates and the resultant climate sensitivity.}, number={6}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Wan, J. S. and Hamilton, D. S. and Mahowald, N. M.}, year={2021}, month={Mar} } @article{kasoar_hamilton_dalmonech_hantson_lasslop_voulgarakis_wells_2021, title={Improved estimates of future fire emissions under CMIP6 scenarios and implications for aerosol radiative forcing}, url={https://doi.org/10.5194/egusphere-egu21-13822}, DOI={10.5194/egusphere-egu21-13822}, abstractNote={The CMIP6 Shared Socioeconomic Pathway (SSP) scenarios include projections of future changes in anthropogenic biomass-burning. Globally, they assume a decrease in total fire emissions over the next century under all scenarios. However, fire regimes and emissions are expected to additionally change with future climate, and the methodology used to project fire emissions in the SSP scenarios is opaque.
We aim to provide a more traceable estimate of future fire emissions under CMIP6 scenarios and evaluate the impacts for aerosol radiative forcing. We utilise interactive wildfire emissions from four independent land-surface models (CLM5, JSBACH3.2, LPJ-GUESS, and ISBA-CTRIP) used within CMIP6 ESMs, and two different machine-learning methods (a random forest, and a generalised additive model) trained on historical data, to predict year 2100 biomass-burning aerosol emissions consistent with the CMIP6-modelled climate for three different scenarios: SSP126, SSP370, and SSP585. This multi-method approach provides future fire emissions integrating information from observations, projections of climate, socioeconomic parameters and changes in vegetation distribution and fuel loads.
Our analysis shows a robust increase in fire emissions for large areas of the extra-tropics until the end of this century for all methods. Although this pattern was present to an extent in the original SSP projections, both the interactive fire models and machine-learning methods predict substantially higher increases in extra-tropical emissions in 2100 than the corresponding SSP datasets. Within the tropics the signal is mixed. Increases in emissions are largely driven by the temperature changes, while in some tropical areas reductions in fire emissions are driven by human factors and changes in precipitation, with the largest reductions in Africa. The machine-learning methods show a stronger reduction in the tropics than the interactive fire models, however overall there is strong agreement between both the models and the machine-learning methods.
We then use additional nudged atmospheric simulations with two state-of-the-art composition-climate models, UKESM1 and CESM2, to diagnose the impact of these updated fire emissions on aerosol burden and radiative forcing, compared with the original SSP prescribed emissions. We provide estimates of future fire radiative forcing, compared to modern-day, under these CMIP6 scenarios which span both the severity of climate change in 2100, and the rate of reduction of other aerosol species.
}, author={Kasoar, Matthew and Hamilton, Douglas and Dalmonech, Daniela and Hantson, Stijn and Lasslop, Gitta and Voulgarakis, Apostolos and Wells, Christopher}, year={2021}, month={Mar} } @article{kok_adebiyi_albani_balkanski_checa-garcia_chin_colarco_hamilton_huang_ito_et al._2021, title={Improved representation of the global dust cycle using observational constraints on dust properties and abundance}, volume={21}, url={https://doi.org/10.5194/acp-21-8127-2021}, DOI={10.5194/acp-21-8127-2021}, abstractNote={Even though desert dust is the most abundant aerosol by mass in Earth's atmosphere, atmospheric models struggle to accurately represent its spatial and temporal distribution. These model errors are partially caused by fundamental difficulties in simulating dust emission in coarse-resolution models and in accurately representing dust microphysical properties. Here we mitigate these problems by developing a new methodology that yields an improved representation of the global dust cycle. We present an analytical framework that uses inverse modeling to integrate an ensemble of global model simulations with observational constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth. We then compare the inverse model results against independent measurements of dust surface concentration and deposition flux and find that errors are reduced by approximately a factor of two relative to current model simulations of the Northern Hemisphere dust cycle. The inverse model results show smaller improvements in the less dusty Southern Hemisphere, most likely because both the model simulations and the observational constraints used in the inverse model are less accurate. On a global basis, we find that the emission flux of dust with geometric diameter up to 20 μm (PM20) is approximately 5,000 Tg/year, which is greater than most models account for. This larger PM20 dust flux is needed to match observational constraints showing a large atmospheric loading of coarse dust. We obtain gridded data sets of dust emission, vertically integrated loading, dust aerosol optical depth, (surface) concentration, and wet and dry deposition fluxes that are resolved by season and particle size. As our results indicate that this data set is more accurate than current model simulations and the MERRA-2 dust reanalysis product, it can be used to improve quantifications of dust impacts on the Earth system.}, number={10}, journal={Atmospheric Chemistry and Physics}, publisher={Copernicus GmbH}, author={Kok, Jasper F. and Adebiyi, Adeyemi A. and Albani, Samuel and Balkanski, Yves and Checa-Garcia, Ramiro and Chin, Mian and Colarco, Peter R. and Hamilton, Douglas S. and Huang, Yue and Ito, Akinori and et al.}, year={2021}, month={May}, pages={8127–8167} } @article{li_mahowald_miller_garcía-pando_klose_hamilton_ageitos_ginoux_balkanski_green_et al._2021, title={Quantifying the range of the dust direct radiative effect due to source mineralogy uncertainty}, url={https://doi.org/10.5194/acp-21-3973-2021}, DOI={10.5194/acp-21-3973-2021}, abstractNote={Abstract. The large uncertainty in the mineral dust direct radiative effect (DRE) hinders projections of future climate change due to anthropogenic activity. Resolving modeled dust mineral speciation allows for spatially and temporally varying refractive indices consistent with dust aerosol composition. Here, for the first time, we quantify the range in dust DRE at the top of the atmosphere (TOA) due to current uncertainties in the surface soil mineralogical content using a dust mineral-resolving climate model. We propagate observed uncertainties in soil mineral abundances from two soil mineralogy atlases along with the optical properties of each mineral into the DRE and compare the resultant range with other sources of uncertainty across six climate models. The shortwave DRE responds region-specifically to the dust burden depending on the mineral speciation and underlying shortwave surface albedo: positively when the regionally averaged annual surface albedo is larger than 0.28 and negatively otherwise. Among all minerals examined, the shortwave TOA DRE and single scattering albedo at the 0.44–0.63 µm band are most sensitive to the fractional contribution of iron oxides to the total dust composition. The global net (shortwave plus longwave) TOA DRE is estimated to be within −0.23 to +0.35 W m−2. Approximately 97 % of this range relates to uncertainty in the soil abundance of iron oxides. Representing iron oxide with solely hematite optical properties leads to an overestimation of shortwave DRE by +0.10 W m−2 at the TOA, as goethite is not as absorbing as hematite in the shortwave spectrum range. Our study highlights the importance of iron oxides to the shortwave DRE: they have a disproportionally large impact on climate considering their small atmospheric mineral mass fractional burden (∼2 %). An improved description of iron oxides, such as those planned in the Earth Surface Mineral Dust Source Investigation (EMIT), is thus essential for more accurate estimates of the dust DRE.}, journal={Atmospheric Chemistry and Physics}, author={Li, Longlei and Mahowald, Natalie M. and Miller, Ron L. and García-Pando, Carlos Pérez and Klose, Martina and Hamilton, Douglas S. and Ageitos, Maria Gonçalves and Ginoux, Paul and Balkanski, Yves and Green, Robert O. and et al.}, year={2021}, month={Mar} } @article{bernstein_hamilton_krasnoff_mahowald_connelly_tilmes_hess_2021, title={Short-term impacts of 2017 western North American wildfires on meteorology, the atmosphere’s energy budget, and premature mortality}, volume={16}, url={https://doi.org/10.1088/1748-9326/ac02ee}, DOI={10.1088/1748-9326/ac02ee}, abstractNote={Abstract Western North American fires have been increasing in magnitude and severity over the last few decades. The complex coupling of fires with the atmospheric energy budget and meteorology creates short-term feedbacks on regional weather altering the amount of pollution to which Americans are exposed. Using a combination of model simulations and observations, this study shows that the severe fires in the summer of 2017 increased atmospheric aerosol concentrations leading to a cooling of the air at the surface, reductions in sensible heat fluxes, and a lowering of the planetary boundary layer height over land. This combination of lower-boundary layer height and increased aerosol pollution from the fires reduces air quality. We estimate that from start of August to end of October 2017, ∼400 premature deaths occurred within the western US as a result of short-term exposure to elevated PM 2.5 from fire smoke. As North America confronts a warming climate with more fires the short-term climate and pollution impacts of increased fire activity should be assessed within policy aimed to minimize impacts of climate change on society.}, number={6}, journal={Environmental Research Letters}, publisher={IOP Publishing}, author={Bernstein, Diana N and Hamilton, Douglas S and Krasnoff, Rosalie and Mahowald, Natalie M and Connelly, David S and Tilmes, Simone and Hess, Peter G M}, year={2021}, month={Jun}, pages={064065} } @article{kok_adebiyi_albani_balkanski_checa-garcia_chin_colarco_hamilton_huang_ito_et al._2021, title={Supplementary material to "Contribution of the world's main dust source regions to the global cycle of desert dust"}, volume={1}, url={https://doi.org/10.5194/acp-2021-4-supplement}, DOI={10.5194/acp-2021-4-supplement}, publisher={Copernicus GmbH}, author={Kok, Jasper F. and Adebiyi, Adeyemi A. and Albani, Samuel and Balkanski, Yves and Checa-Garcia, Ramiro and Chin, Mian and Colarco, Peter R. and Hamilton, Douglas S. and Huang, Yue and Ito, Akinori and et al.}, year={2021}, month={Jan} } @article{achterberg_steigenberger_klar_browning_marsay_painter_vieira_baker_hamilton_tanhua_et al._2021, title={Trace Element Biogeochemistry in the High‐Latitude North Atlantic Ocean: Seasonal Variations and Volcanic Inputs}, volume={35}, url={https://doi.org/10.1029/2020GB006674}, DOI={10.1029/2020GB006674}, abstractNote={We present dissolved and total dissolvable trace elements for spring and summer cruises in 2010 in the high-latitude North Atlantic. Surface and full depth data are provided for Al, Cd, Co, Cu, Mn, Ni, Pb, and Zn in the Iceland and Irminger Basins, and consequences of biological uptake and inputs by the spring Eyjafjallajökull volcanic eruption are assessed. Ash from Eyjafjallajökull resulted in pronounced increases in Al, Mn, and Zn in surface waters in close proximity to Iceland during the eruption, while 3 months later during the summer cruise levels had returned to more typical values for the region. The apparent seasonal removal ratios of surface trace elements were consistent with biological export. Assessment of supply of trace elements to the surface mixed layer for the region, excluding volcanic inputs, indicated that deep winter mixing was the dominant source, with diffusive mixing being a minor source (between 13.5% [dissolved Cd, DCd] and −2.43% [DZn] of deep winter flux), and atmospheric inputs being an important source only for DAl and DZn (DAl up to 42% and DZn up to 4.2% of deep winter + diffusive fluxes) and typically less than 1% for the other elements. Elemental supply ratios to the surface mixed layer through convection were comparable to apparent removal ratios we calculated between spring and summer. Given that deep mixing dominated nutrient and trace element supply to surface waters, predicted increases in water column stratification in this region may reduce supply, with potential consequences for primary production and the biological carbon pump.}, number={3}, journal={Global Biogeochemical Cycles}, publisher={American Geophysical Union (AGU)}, author={Achterberg, Eric P. and Steigenberger, Sebastian and Klar, Jessica K. and Browning, Thomas J. and Marsay, Chris M. and Painter, Stuart C. and Vieira, Lúcia H. and Baker, Alex R. and Hamilton, Douglas S. and Tanhua, Toste and et al.}, year={2021}, month={Mar} } @article{rathod_hamilton_mahowald_klimont_corbett_bond_2020, title={A Mineralogy‐Based Anthropogenic Combustion‐Iron Emission Inventory}, volume={125}, url={https://doi.org/10.1029/2019JD032114}, DOI={10.1029/2019JD032114}, abstractNote={Atmospheric supply of iron can modulate ocean biogeochemistry, due to its key role in global nitrogen and carbon cycles. Current estimates predict up to 20% of global ocean net primary productivity depends on an atmospheric iron source. Using a technology-based methodology, we revise total and soluble anthropogenic iron emissions and resolve iron into its mineral components, which allows modeling mineral-specific atmospheric reactions. We compare different methodologies for representing anthropogenic iron solubility: measured in mild and strong leaches and estimated using a mineralogy basis and identify the emissions that are most affected by such assumptions. The inclusion of metal smelting as an iron source increases iron emissions by up to 10 times higher in the fine aerosol fraction (smaller than 1 μm) than most previous inventories. Different solubility assumptions alter anthropogenic soluble iron emissions and deposition by a factor of 20 and 10, respectively. Using solubilities measured in mild leaches and calculated by mineralogy give 20–30 Gg/yr anthropogenic emissions and 40–50 Gg/yr deposition, while those measured in strong leaches give 80–440 Gg/yr emissions and 200–450 Gg/yr deposition. This range of anthropogenic soluble iron deposition leads to global soluble iron deposition of 1,900–2,300 Gg/yr when dust, wildfires, and atmospheric processing are included, indicating such assumptions can affect global soluble iron supply by about 30%. In regions where marine primary productivity is iron limited, anthropogenic combustion-iron contributes up to half of the atmospheric soluble iron flux to the North Pacific Ocean but supplies less than 5% to the Southern Ocean.}, number={17}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Rathod, S. D. and Hamilton, D. S. and Mahowald, N. M. and Klimont, Z. and Corbett, J. J. and Bond, T. C.}, year={2020}, month={Sep} } @article{hamilton_moore_arneth_bond_carslaw_hantson_ito_kaplan_lindsay_nieradzik_et al._2020, title={Impact of Changes to the Atmospheric Soluble Iron Deposition Flux on Ocean Biogeochemical Cycles in the Anthropocene}, volume={34}, url={https://doi.org/10.1029/2019GB006448}, DOI={10.1029/2019GB006448}, abstractNote={Iron can be a growth-limiting nutrient for phytoplankton, modifying rates of net primary production, nitrogen fixation, and carbon export - highlighting the importance of new iron inputs from the atmosphere. The bioavailable iron fraction depends on the emission source and the dissolution during transport. The impacts of anthropogenic combustion and land use change on emissions from industrial, domestic, shipping, desert, and wildfire sources suggest that Northern Hemisphere soluble iron deposition has likely been enhanced between 2% and 68% over the Industrial Era. If policy and climate follow the intermediate Representative Concentration Pathway 4.5 trajectory, then results suggest that Southern Ocean (>30°S) soluble iron deposition would be enhanced between 63% and 95% by 2100. Marine net primary productivity and carbon export within the open ocean are most sensitive to changes in soluble iron deposition in the Southern Hemisphere; this is predominantly driven by fire rather than dust iron sources. Changes in iron deposition cause large perturbations to the marine nitrogen cycle, up to 70% increase in denitrification and 15% increase in nitrogen fixation, but only modestly impacts the carbon cycle and atmospheric CO2 concentrations (1–3 ppm). Regionally, primary productivity increases due to increased iron deposition are often compensated by offsetting decreases downstream corresponding to equivalent changes in the rate of phytoplankton macronutrient uptake, particularly in the equatorial Pacific. These effects are weaker in the Southern Ocean, suggesting that changes in iron deposition in this region dominates the global carbon cycle and climate response.}, number={3}, journal={Global Biogeochemical Cycles}, publisher={American Geophysical Union (AGU)}, author={Hamilton, Douglas S. and Moore, J. Keith and Arneth, Almut and Bond, Tami C. and Carslaw, Ken S. and Hantson, Stijn and Ito, Akinori and Kaplan, Jed O. and Lindsay, Keith and Nieradzik, Lars and et al.}, year={2020}, month={Mar} } @article{kok_adebiyi_albani_balkanski_checa-garcia_chin_colarco_hamilton_huang_ito_et al._2020, title={Improved representation of the global dust cycle using observational constraints on dust properties and abundance}, volume={11}, url={https://doi.org/10.5194/acp-2020-1131}, DOI={10.5194/acp-2020-1131}, abstractNote={Abstract. Even though desert dust is the most abundant aerosol by mass in Earth's atmosphere, atmospheric models struggle to accurately represent its spatial and temporal distribution. These model errors are partially caused by fundamental difficulties in simulating dust emission in coarse-resolution models and in accurately representing dust microphysical properties. Here we mitigate these problems by developing a new methodology that yields an improved representation of the global dust cycle. We present an analytical framework that uses inverse modeling to integrate an ensemble of global model simulations with observational constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth. We then compare the inverse model results against independent measurements of dust surface concentration and deposition flux and find that errors are reduced by approximately a factor of two relative to current model simulations of the Northern Hemisphere dust cycle. The inverse model results show smaller improvements in the less dusty Southern Hemisphere, most likely because both the model simulations and the observational constraints used in the inverse model are less accurate. On a global basis, we find that the emission flux of dust with geometric diameter up to 20 μm (PM20) is approximately 5,000 Tg/year, which is greater than most models account for. This larger PM20 dust flux is needed to match observational constraints showing a large atmospheric loading of coarse dust. We obtain gridded data sets of dust emission, vertically integrated loading, dust aerosol optical depth, (surface) concentration, and wet and dry deposition fluxes that are resolved by season and particle size. As our results indicate that this data set is more accurate than current model simulations and the MERRA-2 dust reanalysis product, it can be used to improve quantifications of dust impacts on the Earth system.}, publisher={Copernicus GmbH}, author={Kok, Jasper F. and Adebiyi, Adeyemi A. and Albani, Samuel and Balkanski, Yves and Checa-Garcia, Ramiro and Chin, Mian and Colarco, Peter R. and Hamilton, Douglas Stephen and Huang, Yue and Ito, Akinori and et al.}, year={2020}, month={Nov} } @article{li_mahowald_miller_garcía-pando_klose_hamilton_ageitos_ginoux_balkanski_green_et al._2020, title={Quantifying the range of the dust direct radiative effect due to source mineralogy uncertainty}, volume={9}, url={https://doi.org/10.5194/acp-2020-547}, DOI={10.5194/acp-2020-547}, abstractNote={Abstract. The large uncertainty in mineral dust direct radiative effect (DRE) hinders projections of future climate change due to anthropogenic activity. Resolving modelled dust mineral-speciation allows for spatially and temporally varying refractive indices consistent with dust aerosol composition. Here, for the first time, we quantify the range in dust DRE at the top of the atmosphere (TOA) due to current uncertainties in the surface soil mineralogical content using a dust mineral-resolving climate model. We propagate observed uncertainties in soil mineral abundances from two soil mineralogy atlases along with the optical properties of each mineral into the DRE and compare the resultant range with other sources of uncertainty across six climate models. The shortwave DRE responses region-specifically to the dust burden depending on the mineral speciation and underlying shortwave surface albedo; positively when the regionally averaged annual surface albedo is larger than 0.28, and negatively otherwise. Among all minerals examined, the shortwave TOA DRE and single scattering albedo at the 0.44–0.63 µm band are most sensitive to the fractional contribution of iron oxides to the total dust composition. The global net (shortwave plus longwave) TOA DRE is estimated to be within −0.23 to +0.35 W m−2. Approximately 97 % of this range relates to uncertainty in the soil abundance of iron oxides. Representing iron-oxide with solely hematite optical properties leads to an overestimation of shortwave DRE by +0.1 W m−2 at the TOA, as goethite is not as absorbing as hematite in the shortwave spectrum range. Our study highlights the importance of iron oxides to the shortwave DRE: they have a disproportionally large impact on climate considering their small atmospheric mineral mass fractional burden (~2 %). An improved description of iron oxides, such as those planned in the Earth Surface Mineral Dust Source Investigation (EMIT), is thus essential for more accurate estimates of the dust DRE.}, publisher={Copernicus GmbH}, author={Li, Longlei and Mahowald, Natalie M. and Miller, Ron L. and García-Pando, Carlos Pérez and Klose, Martina and Hamilton, Douglas S. and Ageitos, Maria Gonçalves and Ginoux, Paul and Balkanski, Yves and Green, Robert O. and et al.}, year={2020}, month={Sep} } @article{carslaw_scott_yoshioka_hamilton_fiona_folberth_mulcahy_dalvi_balkanski_checa-garcia_et al._2020, title={Re-assessment of pre-industrial fires in CMIP6 models and the implications for radiative forcing}, volume={3}, url={https://doi.org/10.5194/egusphere-egu2020-18190}, DOI={10.5194/egusphere-egu2020-18190}, abstractNote={Assessment of anthropogenic radiative forcing requires a robust understanding of the composition of the pre-industrial baseline atmosphere from which calculations are made
It is often assumed that fire activity and the associated aerosol emissions were lower in the pre-industrial period than in the present day. However, some lines of evidence suggest that fire activity may have halved since the pre-industrial period.
Here we compare the simulated ratio of pre-industrial (c.1750CE and c.1850CE) to present-day black carbon surface concentrations in five ESMs (CNRM-ESM2-1, EC-Earth3, IPSL-CM6, NorESM1.2, UKESM1), using historical fire emissions from the Sixth Coupled Model Intercomparison Project (CMIP6), to the ratio in Northern Hemisphere ice-core records.
We find that when forced with CMIP6 fire emissions all ESMs overestimate the present-day to pre-industrial black carbon ratio. This is consistent with previous studies and suggests that the contribution of fire to the composition of the pre-industrial atmosphere may be too low. If the contrast between the pre-industrial and present-day atmospheres in these models is too great, they are likely to overestimate the strength of the anthropogenic aerosol radiative forcing.
We extend our analysis to include additional ESMs providing historical simulations for CMIP6, as included in the IPCC’s Sixth Assessment Report.
}, publisher={Copernicus GmbH}, author={Carslaw, Ken and Scott, Cat and Yoshioka, Masaru and Hamilton, Douglas and Fiona, O’Connor and Folberth, Gerd and Mulcahy, Jane and Dalvi, Mohit and Balkanski, Yves and Checa-Garcia, Ramiro and et al.}, year={2020}, month={Mar} } @article{hamilton_scanza_rathod_bond_kok_li_matsui_mahowald_2020, title={Recent (1980 to 2015) Trends and Variability in Daily‐to‐Interannual Soluble Iron Deposition from Dust, Fire, and Anthropogenic Sources}, url={https://doi.org/10.1029/2020GL089688}, DOI={10.1029/2020GL089688}, journal={Geophysical Research Letters}, author={Hamilton, Douglas S. and Scanza, Rachel A. and Rathod, Sagar D. and Bond, Tami C. and Kok, Jasper F. and Li, Longlei and Matsui, Hitoshi and Mahowald, Natalie M.}, year={2020}, month={Sep} } @article{kok_adebiyi_albani_balkanski_checa-garcia_chin_colarco_hamilton_huang_ito_et al._2020, title={Supplementary material to "Improved representation of the global dust cycle using observational constraints on dust properties and abundance"}, volume={11}, url={https://doi.org/10.5194/acp-2020-1131-supplement}, DOI={10.5194/acp-2020-1131-supplement}, publisher={Copernicus GmbH}, author={Kok, Jasper F. and Adebiyi, Adeyemi A. and Albani, Samuel and Balkanski, Yves and Checa-Garcia, Ramiro and Chin, Mian and Colarco, Peter R. and Hamilton, Douglas Stephen and Huang, Yue and Ito, Akinori and et al.}, year={2020}, month={Nov} } @article{li_mahowald_miller_garcía-pando_klose_hamilton_ageitos_ginoux_balkanski_green_et al._2020, title={Supplementary material to "Quantifying the range of the dust direct radiative effect due to source mineralogy uncertainty"}, volume={9}, url={https://doi.org/10.5194/acp-2020-547-supplement}, DOI={10.5194/acp-2020-547-supplement}, publisher={Copernicus GmbH}, author={Li, Longlei and Mahowald, Natalie M. and Miller, Ron L. and García-Pando, Carlos Pérez and Klose, Martina and Hamilton, Douglas S. and Ageitos, Maria Gonçalves and Ginoux, Paul and Balkanski, Yves and Green, Robert O. and et al.}, year={2020}, month={Sep} } @article{devlin_eiden_bürgi_macqueen_headlam_brill_carrillo_hamilton_jiang_barcheck_et al._2020, title={The IDEEAS Working Group at Cornell University: A New Framework of Collective Leadership for Promoting Justice, Equity, Diversity, and Inclusion in the Geosciences}, url={https://doi.org/10.1002/essoar.10505326.1}, DOI={10.1002/essoar.10505326.1}, abstractNote={If the university can be thought of as an incubator for ideas and thought leadership, then each department is a learning ecosystem unto itself. The IDEEAS (Inclusion, Diversity, and Equity in Earth...}, author={Devlin, Kelly and Eiden, Elizabeth and Bürgi, Paula and MacQueen, Patricia and Headlam, Carolyn and Brill, Kyle and Carrillo, Carlos and Hamilton, Douglas S and Jiang, Junle and Barcheck, Grace and et al.}, year={2020}, month={Dec} } @article{rowlinson_rap_hamilton_pope_hantson_arnold_kaplan_arneth_chipperfield_forster_et al._2020, title={Tropospheric ozone radiative forcing uncertainty due to pre-industrial fire and biogenic emissions}, url={https://doi.org/10.5194/acp-20-10937-2020}, DOI={10.5194/acp-20-10937-2020}, abstractNote={Abstract. Tropospheric ozone concentrations are sensitive to natural emissions of precursor compounds. In contrast to existing assumptions, recent evidence indicates that terrestrial vegetation emissions in the pre-industrial era were larger than in the present day. We use a chemical transport model and a radiative transfer model to show that revised inventories of pre-industrial fire and biogenic emissions lead to an increase in simulated pre-industrial ozone concentrations, decreasing the estimated pre-industrial to present-day tropospheric ozone radiative forcing by up to 34 % (0.38 to 0.25 W m−2). We find that this change is sensitive to employing biomass burning and biogenic emissions inventories based on matching vegetation patterns, as the co-location of emission sources enhances the effect on ozone formation. Our forcing estimates are at the lower end of existing uncertainty range estimates (0.2–0.6 W m−2), without accounting for other sources of uncertainty. Thus, future work should focus on reassessing the uncertainty range of tropospheric ozone radiative forcing.}, journal={Atmospheric Chemistry and Physics}, author={Rowlinson, Matthew J. and Rap, Alexandru and Hamilton, Douglas S. and Pope, Richard J. and Hantson, Stijn and Arnold, Steve R. and Kaplan, Jed O. and Arneth, Almut and Chipperfield, Martyn P. and Forster, Piers M. and et al.}, year={2020}, month={Sep} } @article{rowlinson_rap_hamilton_pope_hantson_arnold_kaplan_arneth_chipperfield_forster_et al._2020, title={Tropospheric ozone radiative forcing uncertainty due to pre-industrial fire and biogenic emissions}, volume={1}, url={https://doi.org/10.5194/acp-2019-1065}, DOI={10.5194/acp-2019-1065}, abstractNote={Abstract. Tropospheric ozone concentrations are sensitive to natural emissions of precursor compounds. In contrast to existing assumptions, recent evidence indicates that terrestrial vegetation emissions in the pre-industrial were larger than in the present-day. We use a chemical transport model and a radiative transfer model to show that revised inventories of pre-industrial fire and biogenic emissions lead to an increase in simulated pre-industrial ozone concentrations, decreasing the estimated pre-industrial to present-day tropospheric ozone radiative forcing of up to 34 % (0.38 W m-2 to 0.25 W m-2). We find that this change is sensitive to employing biomass burning and biogenic emissions inventories based on matching vegetation patterns, as co-location of emission sources enhances the effect on ozone formation. Our forcing estimates are at the lower end of existing uncertainty range estimates (0.2–0.6 W m-22), without accounting for other sources of uncertainty. Thus, future work should focus on reassessing the uncertainty range of tropospheric ozone radiative forcing.}, publisher={Copernicus GmbH}, author={Rowlinson, Matthew J. and Rap, Alexandru and Hamilton, Douglas S. and Pope, Richard J. and Hantson, Stijn and Arnold, Stephen R. and Kaplan, Jed O. and Arneth, Almut and Chipperfield, Martyn P. and Forster, Piers M. and et al.}, year={2020}, month={Jan} } @article{hamilton_barkley_moore_arneth_bond_carslaw_gaston_hantson_ito_kaplan_et al._2020, title={Underestimated Role of Fires in Providing Nutrients for Biogeochemical Cycles}, volume={3}, url={https://doi.org/10.5194/egusphere-egu2020-10650}, DOI={10.5194/egusphere-egu2020-10650}, abstractNote={
Fire regimes respond to both climate and human land management practice changes, in turn modifying land cover distributions, surface albedo, carbon storage, and emissions. Much attention has recently been given to the health and climate impacts of fires, but fires are also an important source of nutrients, such as iron and phosphorus, to both land and ocean biospheres. Fires therefore create important feedbacks within the Earth system. Here we discuss recent developments showing how fires are a previously underestimated source of limiting nutrients, providing up to half the annual deposited amount of soluble iron and soluble phosphorus to southern oceans and the Amazon, respectively. Fire can therefore stimulate ocean productivity by providing long range transport of essential nutrients, released from the vegetation burned and entrained with dust from the surrounding environment, to remote regions. We considered the impact of human activity on soluble iron deposition for the past (c.1750 CE), present (c.2010 CE), and future (c.2100 CE). We find that the global carbon cycle and climate response is dominated by changes to primary productivity within the Southern Ocean (>30ºS) and that the carbon export efficiency (gram of carbon sequestered per gram of soluble iron added) for this region is 43% larger when altering fire emissions compared to altering dust emissions. Results suggest that modelling past and future changes in biogeochemical cycles should incorporate information on how fires, and the nutrients carried within their plumes, respond to changes in climate.
}, publisher={Copernicus GmbH}, author={Hamilton, Douglas and Barkley, Anne and Moore, J. Keith and Arneth, Almut and Bond, Tami and Carslaw, Kenneth and Gaston, Cassandra and Hantson, Stijn and Ito, Akinori and Kaplan, Jed and et al.}, year={2020}, month={Mar} } @article{barkley_prospero_mahowald_hamilton_popendorf_oehlert_pourmand_gatineau_panechou-pulcherie_blackwelder_et al._2019, title={African biomass burning is a substantial source of phosphorus deposition to the Amazon, Tropical Atlantic Ocean, and Southern Ocean}, volume={116}, url={https://doi.org/10.1073/pnas.1906091116}, DOI={10.1073/pnas.1906091116}, abstractNote={Significance Phosphorus (P) deposition from aerosols can stimulate primary productivity in P-depleted marine and terrestrial ecosystems. We tested the hypothesis that African dust fertilizes the Amazon Basin and Tropical Atlantic Ocean (TAO) by measuring windborne dust, P, and soluble P in samples collected at a coastal site on the northeastern edge of the Amazon. Using satellite data and models, we identified a previously underestimated source of soluble P: biomass burning aerosol transported from southern Africa that can supply P to the Amazon, TAO, and Southern Ocean. Because P associated with biomass burning emissions is more soluble than P in transported dust, biomass burning aerosols immediately impact P cycling and primary production, especially in marine ecosystems like the TAO.}, number={33}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Barkley, Anne E. and Prospero, Joseph M. and Mahowald, Natalie and Hamilton, Douglas S. and Popendorf, Kimberly J. and Oehlert, Amanda M. and Pourmand, Ali and Gatineau, Alexandre and Panechou-Pulcherie, Kathy and Blackwelder, Patricia and et al.}, year={2019}, month={Aug}, pages={16216–16221} } @article{letelier_björkman_church_hamilton_mahowald_scanza_schneider_white_karl_2019, title={Climate-driven oscillation of phosphorus and iron limitation in the North Pacific Subtropical Gyre}, volume={116}, url={https://doi.org/10.1073/pnas.1900789116}, DOI={10.1073/pnas.1900789116}, abstractNote={Significance Characterizing the mechanisms driving spatial and temporal changes in the stoichiometry of nutrient supply is crucial to understand the controls of an ecosystem’s carrying capacity and productivity. In marine oligotrophic regions, small changes in the ocean and atmospheric nutrient input ratio can shift the nature of the limiting nutrient. The present study documents such a shift at interannual scales between periods of phosphorus limitation and sufficiency in the North Pacific Subtropical Gyre. These shifts appear to be driven by interannual variations in the transport of iron-rich Asian dust across the North Pacific resulting from basin-scale changes in atmospheric pressure gradients, as reflected by the Pacific Decadal Oscillation index, causing the ecosystem to oscillate between phosphorus and iron limitation.}, number={26}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Letelier, Ricardo M. and Björkman, Karin M. and Church, Matthew J. and Hamilton, Douglas S. and Mahowald, Natalie M. and Scanza, Rachel A. and Schneider, Niklas and White, Angelicque E. and Karl, David M.}, year={2019}, month={Jun}, pages={12720–12728} } @article{fanourgakis_kanakidou_nenes_bauer_bergman_carslaw_grini_hamilton_johnson_karydis_et al._2019, title={Evaluation of global simulations of aerosol particle and cloud condensation nuclei number, with implications for cloud droplet formation}, volume={19}, url={https://doi.org/10.5194/acp-19-8591-2019}, DOI={10.5194/acp-19-8591-2019}, abstractNote={Abstract. A total of 16 global chemistry transport models and general circulation models have participated in this study; 14 models have been evaluated with regard to their ability to reproduce the near-surface observed number concentration of aerosol particles and cloud condensation nuclei (CCN), as well as derived cloud droplet number concentration (CDNC). Model results for the period 2011–2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments and on the seasonal and short-term variability in the aerosol properties. There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of −24 % and −35 % for particles with dry diameters >50 and >120 nm, as well as −36 % and −34 % for CCN at supersaturations of 0.2 % and 1.0 %, respectively. However, they seem to behave differently for particles activating at very low supersaturations (<0.1 %) than at higher ones. A total of 15 models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N3 (number concentration of particles with dry diameters larger than 3 nm) and up to about 1 for simulated CCN in the extra-polar regions. A global mean reduction of a factor of about 2 is found in the model diversity for CCN at a supersaturation of 0.2 % (CCN0.2) compared to that for N3, maximizing over regions where new particle formation is important. An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter. Models capture the relative amplitude of the seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120 nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40 % during winter and 20 % in summer. In contrast to the large spread in simulated aerosol particle and CCN number concentrations, the CDNC derived from simulated CCN spectra is less diverse and in better agreement with CDNC estimates consistently derived from the observations (average NMB −13 % and −22 % for updraft velocities 0.3 and 0.6 m s−1, respectively). In addition, simulated CDNC is in slightly better agreement with observationally derived values at lower than at higher updraft velocities (index of agreement 0.64 vs. 0.65). The reduced spread of CDNC compared to that of CCN is attributed to the sublinear response of CDNC to aerosol particle number variations and the negative correlation between the sensitivities of CDNC to aerosol particle number concentration (∂Nd/∂Na) and to updraft velocity (∂Nd/∂w). Overall, we find that while CCN is controlled by both aerosol particle number and composition, CDNC is sensitive to CCN at low and moderate CCN concentrations and to the updraft velocity when CCN levels are high. Discrepancies are found in sensitivities ∂Nd/∂Na and ∂Nd/∂w; models may be predisposed to be too “aerosol sensitive” or “aerosol insensitive” in aerosol–cloud–climate interaction studies, even if they may capture average droplet numbers well. This is a subtle but profound finding that only the sensitivities can clearly reveal and may explain inter-model biases on the aerosol indirect effect.}, number={13}, journal={Atmospheric Chemistry and Physics}, publisher={Copernicus GmbH}, author={Fanourgakis, George S. and Kanakidou, Maria and Nenes, Athanasios and Bauer, Susanne E. and Bergman, Tommi and Carslaw, Ken S. and Grini, Alf and Hamilton, Douglas S. and Johnson, Jill S. and Karydis, Vlassis A. and et al.}, year={2019}, month={Jul}, pages={8591–8617} } @article{fanourgakis_kanakidou_nenes_bauer_bergman_carslaw_grini_hamilton_johnson_karydis_et al._2019, title={Evaluation of global simulations of aerosol particle number and cloud condensation nuclei, and implications for cloud droplet formation}, volume={1}, url={https://doi.org/10.5194/acp-2018-1340}, DOI={10.5194/acp-2018-1340}, abstractNote={Abstract. A total of sixteen global chemistry transport models and general circulation models have participated in this study. Fourteen models have been evaluated with regard to their ability to reproduce near-surface observed number concentration of aerosol particle and cloud condensation nuclei (CCN), and derived cloud droplet number concentration (CDNC). Model results for the period 2011–2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations, located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments, and on the seasonal and short-term variability in the aerosol properties. There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of −24 % and −35 % for particles with dry diameters > 50 nm and > 120 nm and −36 % and −34 % for CCN at supersaturations of 0.2 % and 1.0 %, respectively. Fifteen models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N3 (number concentration of particles with dry diameters larger than 3 nm) and up to about 1 for simulated CCN in the extra-polar regions. An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter. Models capture the relative amplitude of seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120 nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40 % during winter and 20 % in summer. In contrast to the large spread in simulated aerosol particle and CCN number concentrations, the CDNC derived from simulated CCN spectra is less diverse and in better agreement with CDNC estimates consistently derived from the observations (average NMB −17 % and −22 % for updraft velocities 0.3 and 0.6 m s−1, respectively). In addition, simulated CDNC is in slightly better agreement with observationally-derived value at lower than at higher updraft velocities (index-of-agreement of 0.47 vs 0.50). The reduced spread of CDNC compared to that of CCN is attributed to the sublinear response of CDNC to aerosol particle number variations and the negative correlation between the sensitivities of CDNC to aerosol particle number concentration and to updraft velocity. Overall, we find that while CCN is controlled by both aerosol particle number and composition, CDNC is sensitive to CCN at low and moderate CCN concentrations and to the updraft velocity when CCN levels are high.}, publisher={Copernicus GmbH}, author={Fanourgakis, George S. and Kanakidou, Maria and Nenes, Athanasios and Bauer, Susanne E. and Bergman, Tommi and Carslaw, Ken S. and Grini, Alf and Hamilton, Douglas S. and Johnson, Jill S. and Karydis, Vlassis A. and et al.}, year={2019}, month={Jan} } @article{tobo_adachi_demott_hill_hamilton_mahowald_nagatsuka_ohata_uetake_kondo_et al._2019, title={Glacially sourced dust as a potentially significant source of ice nucleating particles}, volume={12}, url={https://doi.org/10.1038/s41561-019-0314-x}, DOI={10.1038/s41561-019-0314-x}, number={4}, journal={Nature Geoscience}, publisher={Springer Science and Business Media LLC}, author={Tobo, Yutaka and Adachi, Kouji and DeMott, Paul J. and Hill, Thomas C. J. and Hamilton, Douglas S. and Mahowald, Natalie M. and Nagatsuka, Naoko and Ohata, Sho and Uetake, Jun and Kondo, Yutaka and et al.}, year={2019}, month={Apr}, pages={253–258} } @article{hamilton_scanza_feng_guinness_kok_li_liu_rathod_wan_wu_et al._2019, title={Improved methodologies for Earth system modelling of atmospheric soluble iron and observation comparisons using the Mechanism of Intermediate complexity for Modelling Iron (MIMI v.1.0)}, volume={5}, url={https://doi.org/10.5194/gmd-2019-84}, DOI={10.5194/gmd-2019-84}, abstractNote={Abstract. Herein, we present the description of the Mechanism of Intermediate complexity for Modelling Iron (MIMI). This iron processing module was developed for use within Earth system models and has been updated within a modal aerosol framework from the original implementation in a bulk aerosol model. MIMI simulates the emission and atmospheric processing of two main sources of iron in aerosol prior to deposition: mineral dust and combustion processes. Atmospheric dissolution of insoluble to soluble iron is parametrized by an acidic interstitial reaction and a separate in-cloud reaction scheme based on observations of enhanced aerosol iron solubility in the presence of oxalate. Updates include a more comprehensive treatment of combustion iron emissions, improvements to the iron dissolution scheme, and an improved physical dust mobilization scheme. An extensive dataset consisting predominantly of cruise-based observations was compiled to compare to the model. The annual mean modelled concentration of surface-level total iron compared well with observations, but less so in the soluble fraction where observations are much more variable in space and time. Comparing model and observational data is sensitive to the definition of the average and the temporal and spatial range over which it is calculated. Through statistical analysis and examples, we show that a median or log-normal distribution is preferred when comparing with soluble iron observations. We redefined ocean deposition regions based on dominant iron emission sources and found that the daily variability in soluble iron simulated by MIMI was larger than that of previous model simulations. MIMI simulated a general increase in soluble iron deposition to Southern Hemisphere oceans by a factor of two to four compared with the previous version, which has implications for our understanding of the ocean biogeochemistry of these predominantly iron limited ocean regions.}, publisher={Copernicus GmbH}, author={Hamilton, Douglas S. and Scanza, Rachel A. and Feng, Yan and Guinness, Joe and Kok, Jasper F. and Li, Longlei and Liu, Xiaohong and Rathod, Sagar D. and Wan, Jessica S. and Wu, Mingxuan and et al.}, year={2019}, month={May} } @article{hamilton_scanza_feng_guinness_kok_li_liu_rathod_wan_wu_et al._2019, title={Improved methodologies for Earth system modelling of atmospheric soluble iron and observation comparisons using the Mechanism of Intermediate complexity for Modelling Iron (MIMI v1.0)}, volume={12}, url={https://doi.org/10.5194/gmd-12-3835-2019}, DOI={10.5194/gmd-12-3835-2019}, abstractNote={Abstract. Herein, we present a description of the Mechanism of Intermediate complexity for Modelling Iron (MIMI v1.0). This iron processing module was developed for use within Earth system models and has been updated within a modal aerosol framework from the original implementation in a bulk aerosol model. MIMI simulates the emission and atmospheric processing of two main sources of iron in aerosol prior to deposition: mineral dust and combustion processes. Atmospheric dissolution of insoluble to soluble iron is parameterized by an acidic interstitial aerosol reaction and a separate in-cloud aerosol reaction scheme based on observations of enhanced aerosol iron solubility in the presence of oxalate. Updates include a more comprehensive treatment of combustion iron emissions, improvements to the iron dissolution scheme, and an improved physical dust mobilization scheme. An extensive dataset consisting predominantly of cruise-based observations was compiled to compare to the model. The annual mean modelled concentration of surface-level total iron compared well with observations but less so in the soluble fraction (iron solubility) for which observations are much more variable in space and time. Comparing model and observational data is sensitive to the definition of the average as well as the temporal and spatial range over which it is calculated. Through statistical analysis and examples, we show that a median or log-normal distribution is preferred when comparing with soluble iron observations. The iron solubility calculated at each model time step versus that calculated based on a ratio of the monthly mean values, which is routinely presented in aerosol studies and used in ocean biogeochemistry models, is on average globally one-third (34 %) higher. We redefined ocean deposition regions based on dominant iron emission sources and found that the daily variability in soluble iron simulated by MIMI was larger than that of previous model simulations. MIMI simulated a general increase in soluble iron deposition to Southern Hemisphere oceans by a factor of 2 to 4 compared with the previous version, which has implications for our understanding of the ocean biogeochemistry of these predominantly iron-limited ocean regions.}, number={9}, journal={Geoscientific Model Development}, publisher={Copernicus GmbH}, author={Hamilton, Douglas S. and Scanza, Rachel A. and Feng, Yan and Guinness, Joseph and Kok, Jasper F. and Li, Longlei and Liu, Xiaohong and Rathod, Sagar D. and Wan, Jessica S. and Wu, Mingxuan and et al.}, year={2019}, month={Sep}, pages={3835–3862} } @article{ito_myriokefalitakis_kanakidou_mahowald_scanza_hamilton_baker_jickells_sarin_bikkina_et al._2019, title={Pyrogenic iron: The missing link to high iron solubility in aerosols}, volume={5}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.aau7671}, DOI={10.1126/sciadv.aau7671}, abstractNote={Air pollution creates high Fe solubility in pyrogenic aerosols, raising the flux of biologically essential Fe to the oceans.}, number={5}, journal={SCIENCE ADVANCES}, publisher={American Association for the Advancement of Science (AAAS)}, author={Ito, Akinori and Myriokefalitakis, Stelios and Kanakidou, Maria and Mahowald, Natalie M. and Scanza, Rachel A. and Hamilton, Douglas S. and Baker, Alex R. and Jickells, Timothy and Sarin, Manmohan and Bikkina, Srinivas and et al.}, year={2019}, month={May} } @article{hamilton_2019, title={Response to RC1}, volume={7}, url={https://doi.org/10.5194/gmd-2019-84-AC1}, DOI={10.5194/gmd-2019-84-AC1}, publisher={Copernicus GmbH}, author={Hamilton, Douglas}, year={2019}, month={Jul} } @article{hamilton_2019, title={Response to RC2}, volume={7}, url={https://doi.org/10.5194/gmd-2019-84-AC2}, DOI={10.5194/gmd-2019-84-AC2}, publisher={Copernicus GmbH}, author={Hamilton, Douglas}, year={2019}, month={Jul} } @article{fanourgakis_kanakidou_nenes_bauer_bergman_carslaw_grini_hamilton_johnson_karydis_et al._2019, title={Supplementary material to "Evaluation of global simulations of aerosol particle number and cloud condensation nuclei, and implications for cloud droplet formation"}, volume={1}, url={https://doi.org/10.5194/acp-2018-1340-supplement}, DOI={10.5194/acp-2018-1340-supplement}, publisher={Copernicus GmbH}, author={Fanourgakis, George S. and Kanakidou, Maria and Nenes, Athanasios and Bauer, Susanne E. and Bergman, Tommi and Carslaw, Ken S. and Grini, Alf and Hamilton, Douglas S. and Johnson, Jill S. and Karydis, Vlassis A. and et al.}, year={2019}, month={Jan} } @article{hamilton_scanza_feng_guinness_kok_li_liu_rathod_wan_wu_et al._2019, title={Supplementary material to "Improved methodologies for Earth system modelling of atmospheric soluble iron and observation comparisons using the Mechanism of Intermediate complexity for Modelling Iron (MIMI v.1.0)"}, volume={5}, url={https://doi.org/10.5194/gmd-2019-84-supplement}, DOI={10.5194/gmd-2019-84-supplement}, publisher={Copernicus GmbH}, author={Hamilton, Douglas S. and Scanza, Rachel A. and Feng, Yan and Guinness, Joe and Kok, Jasper F. and Li, Longlei and Liu, Xiaohong and Rathod, Sagar D. and Wan, Jessica S. and Wu, Mingxuan and et al.}, year={2019}, month={May} } @article{conway_hamilton_shelley_aguilar-islas_landing_mahowald_john_2019, title={Tracing and constraining anthropogenic aerosol iron fluxes to the North Atlantic Ocean using iron isotopes}, volume={10}, url={https://doi.org/10.1038/s41467-019-10457-w}, DOI={10.1038/s41467-019-10457-w}, abstractNote={Abstract Atmospheric dust is an important source of the micronutrient Fe to the oceans. Although relatively insoluble mineral Fe is assumed to be the most important component of dust, a relatively small yet highly soluble anthropogenic component may also be significant. However, quantifying the importance of anthropogenic Fe to the global oceans requires a tracer which can be used to identify and constrain anthropogenic aerosols in situ. Here, we present Fe isotope (δ 56 Fe) data from North Atlantic aerosol samples from the GEOTRACES GA03 section. While soluble aerosol samples collected near the Sahara have near-crustal δ 56 Fe, soluble aerosols from near North America and Europe instead have remarkably fractionated δ 56 Fe values (as light as −1.6‰). Here, we use these observations to fingerprint anthropogenic combustion sources, and to refine aerosol deposition modeling. We show that soluble anthropogenic aerosol Fe flux to the global surface oceans is highly likely to be underestimated, even in the dusty North Atlantic.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Conway, Tim M. and Hamilton, Douglas S. and Shelley, Rachel U. and Aguilar-Islas, Ana M. and Landing, William M. and Mahowald, Natalie M. and John, Seth G.}, year={2019}, month={Dec} } @article{mahowald_hamilton_mackey_moore_baker_scanza_zhang_2018, title={Aerosol trace metal leaching and impacts on marine microorganisms}, volume={9}, url={https://doi.org/10.1038/s41467-018-04970-7}, DOI={10.1038/s41467-018-04970-7}, abstractNote={Abstract Metal dissolution from atmospheric aerosol deposition to the oceans is important in enhancing and inhibiting phytoplankton growth rates and modifying plankton community structure, thus impacting marine biogeochemistry. Here we review the current state of knowledge on the causes and effects of the leaching of multiple trace metals from natural and anthropogenic aerosols. Aerosol deposition is considered both on short timescales over which phytoplankton respond directly to aerosol metal inputs, as well as longer timescales over which biogeochemical cycles are affected by aerosols.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Mahowald, Natalie M. and Hamilton, Douglas S. and Mackey, Katherine R. M. and Moore, J. Keith and Baker, Alex R. and Scanza, Rachel A. and Zhang, Yan}, year={2018}, month={Dec} } @article{matsui_mahowald_moteki_hamilton_ohata_yoshida_koike_scanza_flanner_2018, title={Anthropogenic combustion iron as a complex climate forcer}, volume={9}, url={https://doi.org/10.1038/s41467-018-03997-0}, DOI={10.1038/s41467-018-03997-0}, abstractNote={Abstract Atmospheric iron affects the global carbon cycle by modulating ocean biogeochemistry through the deposition of soluble iron to the ocean. Iron emitted by anthropogenic (fossil fuel) combustion is a source of soluble iron that is currently considered less important than other soluble iron sources, such as mineral dust and biomass burning. Here we show that the atmospheric burden of anthropogenic combustion iron is 8 times greater than previous estimates by incorporating recent measurements of anthropogenic magnetite into a global aerosol model. This new estimation increases the total deposition flux of soluble iron to southern oceans (30–90 °S) by 52%, with a larger contribution of anthropogenic combustion iron than dust and biomass burning sources. The direct radiative forcing of anthropogenic magnetite is estimated to be 0.021 W m −2 globally and 0.22 W m −2 over East Asia. Our results demonstrate that anthropogenic combustion iron is a larger and more complex climate forcer than previously thought, and therefore plays a key role in the Earth system.}, number={1}, journal={Nature Communications}, publisher={Springer Nature}, author={Matsui, Hitoshi and Mahowald, Natalie M. and Moteki, Nobuhiro and Hamilton, Douglas S. and Ohata, Sho and Yoshida, Atsushi and Koike, Makoto and Scanza, Rachel A. and Flanner, Mark G.}, year={2018}, month={Dec} } @article{scanza_mahowald_garcia-pando_buck_baker_hamilton_2018, title={Atmospheric Processing of Iron in Mineral and Combustion Aerosols: Development of an Intermediate-Complexity Mechanism Suitable for Earth System Models}, volume={2}, url={https://doi.org/10.5194/acp-2018-80}, DOI={10.5194/acp-2018-80}, abstractNote={Abstract. Atmospheric processing of iron in dust and combustion aerosols is simulated using an intermediate-complexity soluble iron mechanism designed for Earth system models. The solubilization mechanism includes both a dependence on aerosol water pH and in-cloud oxalic acid. The simulations of size resolved total, soluble and fractional iron solubility indicate that this mechanism captures many but not all of the features seen from cruise observations of labile iron. The primary objective was to determine the extent to which our solubility scheme could adequately match observations of fractional iron solubility. We define a semi-quantitative metric as the model mean at points with observations divided by the observational mean (MMO); fractional iron solubility MMO is 0.8, indicating that while the model is not capturing all of the observational variability, it is within range of the observational mean. Several sensitivity studies are performed to ascertain the degree of complexity needed to match observations; including the oxalic acid enhancement is necessary while different parameterizations for calculating model oxalate concentrations are less important. The percent change in soluble iron deposition between the reference case and the simulation with acidic processing alone is 63.8 %, which is consistent with previous studies. Upon deposition to global oceans, global mean combustion iron solubility to total fractional iron solubility is 8.2 %; however, the contribution of fractional iron solubility from combustion sources to ocean basins below 15° S is approximately 50 %. We conclude that in many remote ocean regions, sources of iron from combustion and dust aerosols are equally important. Our estimates of changes in deposition of soluble iron to the ocean since preindustrial suggest roughly a doubling due to a combination of higher dust and combustion iron emissions along with more efficient atmospheric processing.}, publisher={Copernicus GmbH}, author={Scanza, Rachel A. and Mahowald, Natalie M. and Garcia-Pando, Carlos Perez and Buck, Clifton and Baker, Alex and Hamilton, Douglas S.}, year={2018}, month={Feb} } @article{scanza_hamilton_garcia-pando_buck_baker_mahowald_2018, title={Atmospheric processing of iron in mineral and combustion aerosols: development of an intermediate-complexity mechanism suitable for Earth system models}, volume={18}, url={https://doi.org/10.5194/acp-18-14175-2018}, DOI={10.5194/acp-18-14175-2018}, abstractNote={Abstract. Atmospheric processing of iron in dust and combustion aerosols is simulated using an intermediate-complexity soluble iron mechanism designed for Earth system models. The solubilization mechanism includes both a dependence on aerosol water pH and in-cloud oxalic acid. The simulations of size-resolved total, soluble and fractional iron solubility indicate that this mechanism captures many but not all of the features seen from cruise observations of labile iron. The primary objective was to determine the extent to which our solubility scheme could adequately match observations of fractional iron solubility. We define a semi-quantitative metric as the model mean at points with observations divided by the observational mean (MMO). The model is in reasonable agreement with observations of fractional iron solubility with an MMO of 0.86. Several sensitivity studies are performed to ascertain the degree of complexity needed to match observations; including the oxalic acid enhancement is necessary, while different parameterizations for calculating model oxalate concentrations are less important. The percent change in soluble iron deposition between the reference case (REF) and the simulation with acidic processing alone is 63.8 %, which is consistent with previous studies. Upon deposition to global oceans, global mean combustion iron solubility to total fractional iron solubility is 8.2 %; however, the contribution of fractional iron solubility from combustion sources to ocean basins below 15∘ S is approximately 50 %. We conclude that, in many remote ocean regions, sources of iron from combustion and dust aerosols are equally important. Our estimates of changes in deposition of soluble iron to the ocean since preindustrial climate conditions suggest roughly a doubling due to a combination of higher dust and combustion iron emissions along with more efficient atmospheric processing.}, number={19}, journal={Atmospheric Chemistry and Physics}, publisher={Copernicus GmbH}, author={Scanza, Rachel A. and Hamilton, Douglas S. and Garcia-Pando, Carlos Perez and Buck, Clifton and Baker, Alex and Mahowald, Natalie M.}, year={2018}, month={Oct}, pages={14175–14196} } @article{matsui_hamilton_mahowald_2018, title={Black carbon radiative effects highly sensitive to emitted particle size when resolving mixing-state diversity}, volume={9}, url={https://doi.org/10.1038/s41467-018-05635-1}, DOI={10.1038/s41467-018-05635-1}, abstractNote={Post-industrial increases in atmospheric black carbon (BC) have a large but uncertain warming contribution to Earth's climate. Particle size and mixing state determine the solar absorption efficiency of BC and also strongly influence how effectively BC is removed, but they have large uncertainties. Here we use a multiple-mixing-state global aerosol microphysics model and show that the sensitivity (range) of present-day BC direct radiative effect, due to current uncertainties in emission size distributions, is amplified 5-7 times (0.18-0.42 W m-2) when the diversity in BC mixing state is sufficiently resolved. This amplification is caused by the lifetime, core absorption, and absorption enhancement effects of BC, whose variability is underestimated by 45-70% in a single-mixing-state model representation. We demonstrate that reducing uncertainties in emission size distributions and how they change in the future, while also resolving modeled BC mixing state diversity, is now essential when evaluating BC radiative effects and the effectiveness of BC mitigation on future temperature changes.}, number={1}, journal={Nature Communications}, publisher={Springer Nature}, author={Matsui, Hitoshi and Hamilton, Douglas S. and Mahowald, Natalie M.}, year={2018}, month={Dec} } @article{hamilton_hantson_scott_kaplan_pringle_nieradzik_rap_folberth_spracklen_carslaw_2018, title={Reassessment of pre-industrial fire emissions strongly affects anthropogenic aerosol forcing}, volume={9}, url={https://doi.org/10.1038/s41467-018-05592-9}, DOI={10.1038/s41467-018-05592-9}, abstractNote={Abstract Uncertainty in pre-industrial natural aerosol emissions is a major component of the overall uncertainty in the radiative forcing of climate. Improved characterisation of natural emissions and their radiative effects can therefore increase the accuracy of global climate model projections. Here we show that revised assumptions about pre-industrial fire activity result in significantly increased aerosol concentrations in the pre-industrial atmosphere. Revised global model simulations predict a 35% reduction in the calculated global mean cloud albedo forcing over the Industrial Era (1750–2000 CE) compared to estimates using emissions data from the Sixth Coupled Model Intercomparison Project. An estimated upper limit to pre-industrial fire emissions results in a much greater (91%) reduction in forcing. When compared to 26 other uncertain parameters or inputs in our model, pre-industrial fire emissions are by far the single largest source of uncertainty in pre-industrial aerosol concentrations, and hence in our understanding of the magnitude of the historical radiative forcing due to anthropogenic aerosol emissions.}, number={1}, journal={Nature Communications}, publisher={Springer Nature}, author={Hamilton, D. S. and Hantson, S. and Scott, C. E. and Kaplan, J. O. and Pringle, K. J. and Nieradzik, L. P. and Rap, A. and Folberth, G. A. and Spracklen, D. V. and Carslaw, K. S.}, year={2018}, month={Dec} } @article{myriokefalitakis_ito_kanakidou_nenes_krol_mahowald_scanza_hamilton_johnson_meskhidze_et al._2018, title={Reviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison study}, volume={15}, ISSN={["1726-4189"]}, url={https://doi.org/10.5194/bg-15-6659-2018}, DOI={10.5194/bg-15-6659-2018}, abstractNote={Abstract. This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and atmospheric concentrations and the analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry transport (CTMs) and general circulation (GCMs) models participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, “The Atmospheric Input of Chemicals to the Ocean”. The global total Fe (TFe) emission strength in the models is equal to ∼72 Tg Fe yr−1 (38–134 Tg Fe yr−1) from mineral dust sources and around 2.1 Tg Fe yr−1 (1.8–2.7 Tg Fe yr−1) from combustion processes (the sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3) Tg Fe yr−1, accounting for both mineral dust and combustion aerosols. The mean global deposition fluxes into the global ocean are estimated to be in the range of 10–30 and 0.2–0.4 Tg Fe yr−1 for TFe and LFe, respectively, which roughly corresponds to a respective 15 and 0.3 Tg Fe yr−1 for the multi-model ensemble model mean. The model intercomparison analysis indicates that the representation of the atmospheric Fe cycle varies among models, in terms of both the magnitude of natural and combustion Fe emissions as well as the complexity of atmospheric processing parameterizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicates that most models overestimate surface level TFe mass concentrations near dust source regions and tend to underestimate the low concentrations observed in remote ocean regions. All models are able to simulate the tendency of higher Fe concentrations near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere (∼14), larger than that of the Southern Hemisphere (∼2.4) for the ensemble model mean. This model intercomparison and model–observation comparison study reveals two critical issues in LFe simulations that require further exploration: (1) the Fe-containing aerosol size distribution and (2) the relative contribution of dust and combustion sources of Fe to labile Fe in atmospheric aerosols over the remote oceanic regions.}, number={21}, journal={BIOGEOSCIENCES}, publisher={Copernicus GmbH}, author={Myriokefalitakis, Stelios and Ito, Akinori and Kanakidou, Maria and Nenes, Athanasios and Krol, Maarten C. and Mahowald, Natalie M. and Scanza, Rachel A. and Hamilton, Douglas S. and Johnson, Matthew S. and Meskhidze, Nicholas and et al.}, year={2018}, month={Nov}, pages={6659–6684} } @article{scanza_mahowald_garcia-pando_buck_baker_hamilton_2018, title={Supplementary material to "Atmospheric Processing of Iron in Mineral and Combustion Aerosols: Development of an Intermediate-Complexity Mechanism Suitable for Earth System Models"}, volume={2}, url={https://doi.org/10.5194/acp-2018-80-supplement}, DOI={10.5194/acp-2018-80-supplement}, publisher={Copernicus GmbH}, author={Scanza, Rachel A. and Mahowald, Natalie M. and Garcia-Pando, Carlos Perez and Buck, Clifton and Baker, Alex and Hamilton, Douglas S.}, year={2018}, month={Feb} } @article{myriokefalitakis_ito_kanakidou_nenes_krol_mahowald_scanza_hamilton_johnson_meskhidze_et al._2018, title={Supplementary material to "The GESAMP atmospheric iron deposition model intercomparison study"}, volume={7}, url={https://doi.org/10.5194/bg-2018-285-supplement}, DOI={10.5194/bg-2018-285-supplement}, publisher={Copernicus GmbH}, author={Myriokefalitakis, Stelios and Ito, Akinori and Kanakidou, Maria and Nenes, Athanasios and Krol, Maarten C. and Mahowald, Natalie M. and Scanza, Rachel A. and Hamilton, Douglas S. and Johnson, Matthew S. and Meskhidze, Nicholas and et al.}, year={2018}, month={Jul} } @article{myriokefalitakis_ito_kanakidou_nenes_krol_mahowald_scanza_hamilton_johnson_meskhidze_et al._2018, title={The GESAMP atmospheric iron deposition model intercomparison study}, volume={7}, url={https://doi.org/10.5194/bg-2018-285}, DOI={10.5194/bg-2018-285}, abstractNote={Abstract. This work reports on the current status of global modelling of iron (Fe) deposition fluxes and atmospheric concentrations and analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry-transport (CTMs) and general circulation (GCMs) models have participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, The Atmospheric Input of Chemicals to the Ocean. The global total Fe (TFe) emissions strength in the models is equal to ~ 72 Tg-Fe yr−1 (38–134 Tg-Fe yr−1) from mineral dust sources and around 2.1 Tg-Fe yr−1 (1.8–2.7 Tg-Fe yr−1) from combustion processes (sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3) Tg-Fe yr−1, accounting for mineral dust and combustion aerosols together. The multi model ensemble global TFe and LFe deposition fluxes into the global ocean are calculated to be ~ 15 Tg-Fe yr−1 and ~ 0.3 Tg-Fe yr−1, respectively. The model intercomparison analysis indicates that the representation of the atmospheric Fe cycle varies among models, in terms of both the magnitude of natural and combustion Fe emissions as well as the complexity of atmospheric processing parametrizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicate that most models overestimate surface level TFe mass concentrations near the dust source regions and tend to underestimate the low concentrations observed in remote ocean regions. All models are able to simulate the tendency of higher Fe loading near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere (~ 14), larger than the Southern Hemisphere (~ 2.4) for the ensemble model mean. This model intercomparison and model–observation comparison study reveals two critical issues in LFe simulations that require further exploration: 1) the Fe-containing aerosol size distribution and 2) the relative contribution of dust and combustion sources of Fe to labile Fe in atmospheric aerosols over the remote oceanic regions.}, publisher={Copernicus GmbH}, author={Myriokefalitakis, Stelios and Ito, Akinori and Kanakidou, Maria and Nenes, Athanasios and Krol, Maarten C. and Mahowald, Natalie M. and Scanza, Rachel A. and Hamilton, Douglas S. and Johnson, Matthew S. and Meskhidze, Nicholas and et al.}, year={2018}, month={Jul} } @article{carslaw_gordon_hamilton_johnson_regayre_yoshioka_pringle_2017, title={Aerosols in the Pre-industrial Atmosphere}, volume={3}, url={http://dx.doi.org/10.1007/s40641-017-0061-2}, DOI={10.1007/s40641-017-0061-2}, abstractNote={We assess the current understanding of the state and behaviour of aerosols under pre-industrial conditions and the importance for climate.Studies show that the magnitude of anthropogenic aerosol radiative forcing over the industrial period calculated by climate models is strongly affected by the abundance and properties of aerosols in the pre-industrial atmosphere. The low concentration of aerosol particles under relatively pristine conditions means that global mean cloud albedo may have been twice as sensitive to changes in natural aerosol emissions under pre-industrial conditions compared to present-day conditions. Consequently, the discovery of new aerosol formation processes and revisions to aerosol emissions have large effects on simulated historical aerosol radiative forcing.We review what is known about the microphysical, chemical, and radiative properties of aerosols in the pre-industrial atmosphere and the processes that control them. Aerosol properties were controlled by a combination of natural emissions, modification of the natural emissions by human activities such as land-use change, and anthropogenic emissions from biofuel combustion and early industrial processes. Although aerosol concentrations were lower in the pre-industrial atmosphere than today, model simulations show that relatively high aerosol concentrations could have been maintained over continental regions due to biogenically controlled new particle formation and wildfires. Despite the importance of pre-industrial aerosols for historical climate change, the relevant processes and emissions are given relatively little consideration in climate models, and there have been very few attempts to evaluate them. Consequently, we have very low confidence in the ability of models to simulate the aerosol conditions that form the baseline for historical climate simulations. Nevertheless, it is clear that the 1850s should be regarded as an early industrial reference period, and the aerosol forcing calculated from this period is smaller than the forcing since 1750. Improvements in historical reconstructions of natural and early anthropogenic emissions, exploitation of new Earth system models, and a deeper understanding and evaluation of the controlling processes are key aspects to reducing uncertainties in future.}, number={1}, journal={Current Climate Change Reports}, publisher={Springer Science and Business Media LLC}, author={Carslaw, Kenneth S. and Gordon, Hamish and Hamilton, Douglas S. and Johnson, Jill S. and Regayre, Leighton A. and Yoshioka, M. and Pringle, Kirsty J.}, year={2017}, month={Mar}, pages={1–15} } @article{hamilton_2015, title={Natural aerosols and climate: Understanding the unpolluted atmosphere to better understand the impacts of pollution}, volume={70}, url={http://dx.doi.org/10.1002/wea.2540}, DOI={10.1002/wea.2540}, abstractNote={Natural aerosols define a pre-industrial baseline state from which the magnitude of anthropogenic aerosol effects on climate are calculated and are a major component of the large uncertainty in anthropogenic aerosol-cloud radiative forcing. This uncertainty would be reduced if aerosol environments unperturbed by air pollution could be studied in the present-day atmosphere, but the pervasiveness of air pollution makes identification of unperturbed regions difficult. This study uses global model simulations to show where aerosol concentrations have remained similar between 1750 and 2000. Four suitable measurement stations are then identified in regions with a pristine-like aerosol state.}, number={9}, journal={Weather}, publisher={Wiley}, author={Hamilton, Douglas S.}, year={2015}, month={Sep}, pages={264–268} } @article{hamilton_lee_pringle_reddington_spracklen_carslaw_2014, title={Occurrence of pristine aerosol environments on a polluted planet}, volume={111}, url={http://dx.doi.org/10.1073/pnas.1415440111}, DOI={10.1073/pnas.1415440111}, abstractNote={Significance Uncertainty in aerosol forcing of climate since the preindustrial era hampers efforts to quantify the sensitivity of global temperature to radiative perturbations caused by human activity. Because forcings are referenced to preindustrial conditions, a large part of the uncertainty will be reduced only by accurately defining pristine aerosol conditions before air pollution. We show that pristine conditions should still be observable on a few days per month in many regions of the Earth. However, pristine cloudy regions, which are of most importance for forcing uncertainty, occur almost entirely in the Southern Hemisphere. Reduction in uncertainty of predominantly Northern Hemisphere forcing may therefore have to rely on measurements from a different hemisphere, which will limit the extent to which uncertainties can be reduced.}, number={52}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Hamilton, Douglas S. and Lee, Lindsay A. and Pringle, Kirsty J. and Reddington, Carly L. and Spracklen, Dominick V. and Carslaw, Kenneth S.}, year={2014}, month={Dec}, pages={18466–18471} } @article{martino_hamilton_baker_jickells_bromley_nojiri_quack_boyd_2014, title={Western Pacific atmospheric nutrient deposition fluxes, their impact on surface ocean productivity}, volume={28}, url={http://dx.doi.org/10.1002/2013gb004794}, DOI={10.1002/2013gb004794}, abstractNote={The atmospheric deposition of both macronutrients and micronutrients plays an important role in driving primary productivity, particularly in the low-latitude ocean. We report aerosol major ion measurements for five ship-based sampling campaigns in the western Pacific from ~25°N to 20°S and compare the results with those from Atlantic meridional transects (~50°N to 50°S) with aerosols collected and analyzed in the same laboratory, allowing full incomparability. We discuss sources of the main nutrient species (nitrogen (N), phosphorus (P), and iron (Fe)) in the aerosols and their stoichiometry. Striking north–south gradients are evident over both basins with the Northern Hemisphere more impacted by terrestrial dust sources and anthropogenic emissions and the North Atlantic apparently more impacted than the North Pacific. We estimate the atmospheric supply rates of these nutrients and the potential impact of the atmospheric deposition on the tropical western Pacific. Our results suggest that the atmospheric deposition is P deficient relative to the needs of the resident phytoplankton. These findings suggest that atmospheric supply of N, Fe, and P increases primary productivity utilizing some of the residual excess phosphorus (P*) in the surface waters to compensate for aerosol P deficiency. Regional primary productivity is further enhanced via the stimulation of nitrogen fixation fuelled by the residual atmospheric iron and P*. Our stoichiometric calculations reveal that a P* of 0.1 µmol L−1 can offset the P deficiency in atmospheric supply for many months. This study suggests that atmospheric deposition may sustain ~10% of primary production in both the western tropical Pacific.}, number={7}, journal={Global Biogeochemical Cycles}, publisher={American Geophysical Union (AGU)}, author={Martino, M. and Hamilton, D. and Baker, A. R. and Jickells, T. D. and Bromley, T. and Nojiri, Y. and Quack, B. and Boyd, P. W.}, year={2014}, month={Jul}, pages={712–728} }