@article{huang_aarons_koffman_cheng_hanschka_munk_jenckes_norris_arendt_2024, title={Role of Source, Mineralogy, and Organic Complexation on Lability and Fe Isotopic Composition of Terrestrial Fe sources to the Gulf of Alaska}, ISSN={["2472-3452"]}, DOI={10.1021/acsearthspacechem.3c00338}, abstractNote={Iron (Fe) is a key trace nutrient supporting marine primary production, and its deposition in the surface ocean can impact multiple biogeochemical cycles. Understanding Fe cycling in the subarctic is key for tracking the fate of particulate-bound sources of oceans in a changing climate. Recently, Fe isotope ratios have been proposed as a potential tool to trace sources of Fe to the marine environment. Here, we investigate the Fe isotopic composition of terrestrial sources of Fe including glacial sediment, loess, volcanic ash, and wildfire aerosols, all from Alaska. Results show that the δ}, journal={ACS EARTH AND SPACE CHEMISTRY}, author={Huang, Linqing and Aarons, Sarah M. and Koffman, Bess G. and Cheng, Wenhan and Hanschka, Lena and Munk, Lee Ann and Jenckes, Jordan and Norris, Emmet and Arendt, Carli A.}, year={2024}, month={Jun} }
 @article{conroy_heikoop_lathrop_musa_newman_xu_mccaully_arendt_salmon_breen_et al._2023, title={Environmental controls on observed spatial variability of soil pore water geochemistry in small headwater catchments underlain with permafrost}, volume={17}, ISSN={["1994-0424"]}, DOI={10.5194/tc-17-3987-2023}, abstractNote={Abstract. Soil pore water (SPW) chemistry can vary substantially across
multiple scales in Arctic permafrost landscapes. The magnitude of these
variations and their relationship to scale are critical considerations for
understanding current controls on geochemical cycling and for predicting
future changes. These aspects are especially important for Arctic change
modeling where accurate representation of sub-grid variability may be
necessary to predict watershed-scale behaviors. Our research goal is to
characterize intra- and inter-watershed soil water geochemical variations at
two contrasting locations in the Seward Peninsula of Alaska, USA. We then
attempt to identify the key factors controlling concentrations of important
pore water solutes in these systems. The SPW geochemistry of 18 locations
spanning two small Arctic catchments was examined for spatial variability
and its dominant environmental controls. The primary environmental controls
considered were vegetation, soil moisture and/or redox condition, water–soil
interactions and hydrologic transport, and mineral solubility. The sampling
locations varied in terms of vegetation type and canopy height, presence or
absence of near-surface permafrost, soil moisture, and hillslope position.
Vegetation was found to have a significant impact on SPW NO3-
concentrations, associated with the localized presence of nitrogen-fixing
alders and mineralization and nitrification of leaf litter from tall willow
shrubs. The elevated NO3- concentrations were, however, frequently
equipoised by increased microbial denitrification in regions with sufficient
moisture to support it. Vegetation also had an observable impact on soil-moisture-sensitive constituents, but the effect was less significant. The
redox conditions in both catchments were generally limited by Fe reduction,
seemingly well-buffered by a cache of amorphous Fe hydroxides, with the most
reducing conditions found at sampling locations with the highest soil
moisture content. Non-redox-sensitive cations were affected by a wide
variety of water–soil interactions that affect mineral solubility and
transport. Identification of the dominant controls on current SPW
hydrogeochemistry allows for qualitative prediction of future geochemical
trends in small Arctic catchments that are likely to experience warming and
permafrost thaw. As source areas for geochemical fluxes to the broader
Arctic hydrologic system, geochemical processes occurring in these
environments are particularly important to understand and predict with
regards to such environmental changes.
                    }, number={9}, journal={CRYOSPHERE}, author={Conroy, Nathan Alec and Heikoop, Jeffrey M. and Lathrop, Emma and Musa, Dea and Newman, Brent D. and Xu, Chonggang and Mccaully, Rachael E. and Arendt, Carli A. and Salmon, Verity G. and Breen, Amy and et al.}, year={2023}, month={Sep}, pages={3987–4006} }
 @article{huang_tissot_ibanez-mejia_forsch_arendt_choy_aarons_2024, title={High-precision zirconium isotope analysis of Pacific seawater reveals large mass-dependent fractionations in the ocean}, volume={365}, ISSN={["1872-9533"]}, DOI={10.1016/j.gca.2023.11.018}, abstractNote={Zirconium (Zr) stable isotopes recently emerged as potential tracers of magmatic processes and, as a result, their behavior in high-temperature environments have been the focus of extensive characterization. In contrast, few studies have focused on Zr behavior and isotopic fractionation in low temperature or aqueous environments. Here, we describe a new analytical routine for highly precise and accurate analysis of Zr isotopes of water samples, using a combination of double-spike and iron co-precipitation methods. To assess the impact of potential systematic biases a series of experiments were conducted on natural and synthetic water samples. Our results show that the spike-to-sample ratio, matrix composition, and high field-strength element (HFSE) concentration have negligible effects on measured seawater Zr isotopic compositions, and that the Fe co-precipitation method used yields to accurate and precise Zr isotope data. We thus apply this method to natural seawater samples collected from a water column profile in the Pacific Ocean off the coast of California, with depths ranging from 5 to 711 m. We find that the natural seawater samples are highly fractionated relative to solid-Earth values and display marked variability in δ94/90Zr as a function of depth, ranging from ∼ +0.650 ‰ near the surface, to +1.530 ‰ near the profile bottom, with an analytical uncertainty of ± ∼0.045 ‰ (2 SE, external reproducibility). The δ94/90Zr value of seawater is much higher than that of Earth's mantle and continental crust, which has a δ94/90Zr value near zero, indicating the presence of processes in the hydrosphere capable of inducing large mass-dependent fractionation. Furthermore, the seawater δ94/90Zr value exhibits systematic variations with respect to water depth and salinity, suggesting that Zr isotopic compositions may be sensitive to seawater chemical properties and source highlighting its potential utility as a tracer of biogeochemical processes within the ocean.}, journal={GEOCHIMICA ET COSMOCHIMICA ACTA}, author={Huang, Linqing and Tissot, Francois L. H. and Ibanez-Mejia, Mauricio and Forsch, Kiefer O. and Arendt, Carli and Choy, C. Anela and Aarons, Sarah M.}, year={2024}, month={Jan}, pages={202–214} }
 @article{pappala_arendt_harmon_2023, title={Spatial characterization of chemical weathering in a proglacial river system, southcentral Alaska}, volume={629}, ISSN={["1872-6836"]}, DOI={10.1016/j.chemgeo.2023.121462}, abstractNote={Major constituent concentrations (Na+, K+, Ca2+, Mg2+, HCO3−, SO42−, Cl−, NO3−) were determined for a 121 km reach of the proglacial Matanuska River, associated tributaries, and five additional glacial rivers on the Kenai Peninsula of southcentral Alaska during peak flow conditions in July 2019. Mass balance and mixing models were utilized to gain insight to chemical weathering processes and carbon feedback implications along the sampling transect. Solute compositions of the Matanuska River varied spatially, shifting from carbonate dominance near the terminus of the Matanuska Glacier to a carbonate-silicate weathering signature in the lower reaches of the river. Geochemical modeling suggests that carbonate dissolution closest to the Matanuska Glacier terminus is driven by sulfuric acid produced from the oxidation of sulfide minerals in the subglacial and proglacial system that acts as a source of CO2. This contrasts with the lower reaches of the Matanuska River, its tributaries, and other Kenai glacial rivers, where mineral dissolution is dominated by carbonic acid and weathering acts as a sink of atmospheric CO2. The spatial variations observed in stream and river compositions are predominantly attributed to the local lithological variations across the catchment, with subglacial weathering signatures observed in the meltwater solute compositions closest to the Matanuska Glacier terminus. This study highlights the importance of spatial sampling in proglacial systems, as proglacial water chemical signatures and carbon feedback implications can shift significantly away from the glacial terminus.}, journal={CHEMICAL GEOLOGY}, author={Pappala, Venkata Sailaja and Arendt, Carli A. and Harmon, Russell S.}, year={2023}, month={Jul} }
 @article{conroy_dann_newman_heikoop_arendt_busey_wilson_wullschleger_2022, title={Chemostatic concentration-discharge behaviour observed in a headwater catchment underlain with discontinuous permafrost}, volume={36}, ISSN={["1099-1085"]}, DOI={10.1002/hyp.14591}, abstractNote={AbstractConcentration–discharge dynamics were evaluated in a small (~ 2.25 km2) headwater catchment underlain with discontinuous permafrost on the Seward Peninsula of western Alaska. A large storm, during which 48 mm of rain fell over a 24‐h period, enabled the evaluation of solute concentration–discharge response to a sizeable hydrological event, while water stable isotopes enabled an appraisal of the contributions of event water. Under normal catchment conditions, chemostatic behaviour was observed for solutes typically derived from mineral weathering (e.g. calcium, magnesium, sodium and silica). The chemostatic behaviour observed for most solutes under normal catchment conditions indicated that catchment storage and residence times are sufficiently long for many solute generating reactions to approach equilibrium. Following the storm however, most solutes exhibited dilutive and highly variable behaviour. This likely indicated the exceedance of a discharge threshold where chemostatic behaviour could no longer be maintained for most solutes. Dissolved organic carbon and silica were the only solutes monitored to exhibit chemostatic behaviour during all time periods.}, number={5}, journal={HYDROLOGICAL PROCESSES}, author={Conroy, Nathan A. and Dann, Julian B. and Newman, Brent D. and Heikoop, Jeffrey M. and Arendt, Carli and Busey, Bob and Wilson, Cathy J. and Wullschleger, Stan D.}, year={2022}, month={May} }
 @article{mccaully_arendt_newman_salmon_heikoop_wilson_sevanto_wales_perkins_marina_et al._2022, title={High nitrate variability on an Alaskan permafrost hillslope dominated by alder shrubs}, volume={16}, ISSN={["1994-0424"]}, DOI={10.5194/tc-16-1889-2022}, abstractNote={Abstract. In Arctic ecosystems, increasing temperatures are driving
the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The
implications of this expansion to the biogeochemistry of Arctic ecosystems
are of critical importance and more work is needed to better understand the
form, availability, and transportation potential of N from these shrubs
across a variety of Arctic landscapes. To gain insights into the processes
controlling N within a permafrost hillslope system, the spatiotemporal
variability of nitrate (NO3-) and its environmental controls were
investigated at an alder (Alnus viridis spp. fruticosa) dominated permafrost tundra landscape in the
Seward Peninsula, Alaska, USA. Soil pore water was collected from locations
within alder shrubland growing along a well-drained hillslope and was compared to soil
pore water collected from locations outside (upslope, downslope, and between) the alder shrubland. Soil pore water
collected within alder shrubland had an average NO3-N (nitrogen from
nitrate) concentration of 4.27±8.02 mg L−1 and differed
significantly from locations outside alder shrubland (0.23±0.83 mg L−1; p<0.05). Temporal variation in NO3-N within and
downslope of alder shrubland co-occurred with precipitation events where
NO3- that accumulated in the soil was likely flushed downslope
during rainfall. These findings have important implications for nutrient
availability and mobility in N-limited permafrost systems that are
experiencing shrub expansion in response to a warming Arctic.
                    }, number={5}, journal={CRYOSPHERE}, author={McCaully, Rachael E. and Arendt, Carli A. and Newman, Brent D. and Salmon, Verity G. and Heikoop, Jeffrey M. and Wilson, Cathy J. and Sevanto, Sanna and Wales, Nathan A. and Perkins, George B. and Marina, Oana C. and et al.}, year={2022}, month={May}, pages={1889–1901} }
 @article{rudolph_arendt_hounshell_paerl_osburn_2020, title={Use of Geospatial, Hydrologic, and Geochemical Modeling to Determine the Influence of Wetland-Derived Organic Matter in Coastal Waters in Response to Extreme Weather Events}, volume={7}, ISSN={["2296-7745"]}, DOI={10.3389/fmars.2020.00018}, abstractNote={Flooding from extreme weather events (EWE), such as hurricanes, exports large amounts of dissolved organic matter (DOM) to both estuaries and coastal waters globally. Hydrologic connectivity of wetlands to adjacent river channels during flood events can potentially have a major control on the DOM exported to coastal waters after EWEs. In this study, a geographic information system based flood model was used to: (1) determine the volume of flooded wetlands in a river corridor following Hurricane Matthew in 2016; (2) compute the resulting volume fluxes of DOM to the Neuse River Estuary-Pamlico Sound (NRE-PS), in eastern North Carolina and (3) use the flood model to quantify the wetland contribution to DOM export. The flood model-derived contributions were validated with a Bayesian Monte Carlo mixing model combining measurements of DOM quality: specific UV Absorbance at 254 nm (SUVA254), spectral slope ratio (SR), and stable isotope ratios of dissolved organic carbon (δ13C-DOC). Results indicated that (1) hydrologic connectivity of the freshwater riparian wetlands caused the wetlands to become the primary source of organic matter (OM) that was exported into the NRE-PS after Matthew and (2) this source lingered in these coastal waters in the months after the storm. Thus, in consideration of the pulse-shunt concept, EWE such as Hurricane Matthew cause pulses of DOM from wetlands, which were the primary source of the OM shunted from the terrestrial environment to the estuary and sound. Wetlands constituted ca. 48% of the annual loading of DOC into the NRE and 16% of DOC loading into the PS over a period of 30 days after Hurricane Matthew. Results were consistent with prior studies in this system, and other coastal ecosystems, that attributed a high reactivity of DOM as the underlying reason for large CO2 releases following EWE. Adapting the pulse-shunt concept to estuaries requires the addition of a “processing” step to account for the DOM to CO2 dynamics, thus a new pulse-shunt process is proposed to incorporate coastal waters. Our results suggest that with increasing frequency and intensity of EWE, strengthening of the lateral transfer of DOM from land to ocean will occur and has the potential to greatly impact coastal carbon cycling.}, journal={FRONTIERS IN MARINE SCIENCE}, author={Rudolph, Jacob C. and Arendt, Carli A. and Hounshell, Alexandria G. and Paerl, Hans W. and Osburn, Christopher L.}, year={2020}, month={Feb} }
 @article{arendt_aciego_sims_das_sheik_stevenson_2018, title={Influence of glacial meltwater on global seawater delta U-234}, volume={225}, ISSN={["1872-9533"]}, DOI={10.1016/j.gca.2018.01.007}, abstractNote={We present the first published uranium-series measurements from modern Greenland Ice Sheet (GrIS) runoff and proximal seawater, and investigate the influence of glacial melt on global seawater δ234U over glacial-interglacial (g-ig) timescales. Climate reconstructions based on closed-system uranium-thorium (U/Th) dating of fossil corals assume U chemistry of seawater has remained stable over time despite notable fluctuations in major elemental compositions, concentrations, and isotopic compositions of global seawater on g-ig timescales. Deglacial processes increase weathering, significantly increasing U-series concentrations and changing the δ234U of glacial meltwater. Analyses of glacial discharge from GrIS outlet glaciers indicate that meltwater runoff has elevated U concentrations and differing 222Rn concentrations and δ234U compositions, likely due to variations in subglacial residence time. Locations with high δ234U have the potential to increase proximal seawater δ234U. To better understand the impact of bulk glacial melt on global seawater δ234U over time, we use a simple box model to scale these processes to periods of extreme deglaciation. We account for U fluxes from the GrIS, Antarctica, and large Northern Hemisphere Continental Ice Sheets, and assess sensitivity by varying melt volumes, duration and U flux input rates based on modern subglacial water U concentrations and compositions. All scenarios support the hypothesis that global seawater δ234U has varied by more than 1‰ through time as a function of predictable perturbations in continental U fluxes during g-ig periods.}, journal={GEOCHIMICA ET COSMOCHIMICA ACTA}, author={Arendt, Carli A. and Aciego, Sarah M. and Sims, Kenneth W. W. and Das, Sarah B. and Sheik, Cody and Stevenson, Emily I.}, year={2018}, month={Mar}, pages={102–115} }
 @article{aarons_aciego_arendt_blakowski_steigmeyer_gabrielli_sierra-hernández_beaudon_delmonte_baccolo_et al._2017, title={Dust composition changes from Taylor Glacier (East Antarctica) during the last glacial-interglacial transition: A multi-proxy approach}, volume={162}, ISSN={0277-3791}, url={http://dx.doi.org/10.1016/J.QUASCIREV.2017.03.011}, DOI={10.1016/J.QUASCIREV.2017.03.011}, abstractNote={Mineral dust is transported in the atmosphere and deposited in oceans, ice sheets and the terrestrial biosphere. Temporal changes in locations of dust source areas and transport pathways have implications for global climate and biogeochemical cycles. The chemical and physical characterization of the dust record preserved in ice cores is useful for identifying of dust source regions, dust transport, dominant wind direction and storm trajectories. Here, we present a 50,000-year geochemical characterization of mineral dust entrapped in a horizontal ice core from the Taylor Glacier in East Antarctica. Strontium (Sr) and neodymium (Nd) isotopes, grain size distribution, trace and rare earth element (REE) concentrations, and inorganic ion (Cl− and Na+) concentrations were measured in 38 samples, corresponding to a time interval from 46 kyr before present (BP) to present. The Sr and Nd isotope compositions of insoluble dust in the Taylor Glacier ice shows distinct changes between the Last Glacial Period (LGP in this study ranging from ∼46.7–15.3 kyr BP) the early Holocene (in this study ranging from ∼14.5–8.7 kyr BP), and zero-age samples. The 87Sr/86Sr isotopic composition of dust in the Taylor Glacier ice ranged from 0.708 to 0.711 during the LGP, while the variability during the early Holocene is higher ranging from 0.707 to 0.714. The εNd composition ranges from 0.1 to −3.9 during the LGP, and is more variable from 1.9 to −8.2 during the early Holocene. The increased isotopic variability during the early Holocene suggests a shift in dust provenance coinciding with the major climate transition from the LGP to the Holocene. The isotopic composition and multiple physical and chemical constraints support previous work attributing Southern South America (SSA) as the main dust source to East Antarctica during the LGP, and a combination of both local Ross Sea Sector dust sources and SSA after the transition into the Holocene. This study provides the first high time resolution data showing variations in dust provenance to East Antarctic ice during a major climate regime shift, and we provide evidence of changes in the atmospheric transport pathways of dust following the last deglaciation.}, journal={Quaternary Science Reviews}, publisher={Elsevier BV}, author={Aarons, Sarah M. and Aciego, Sarah M. and Arendt, Carli A. and Blakowski, Molly A. and Steigmeyer, August and Gabrielli, Paolo and Sierra-Hernández, M. Roxana and Beaudon, Emilie and Delmonte, Barbara and Baccolo, Giovanni and et al.}, year={2017}, month={Apr}, pages={60–71} }
 @article{arendt_aciego_sims_aarons_2017, title={Seasonal progression of uranium series isotopes in subglacial meltwater: Implications for subglacial storage time}, volume={467}, ISSN={["1872-6836"]}, DOI={10.1016/j.chemgeo.2017.07.007}, abstractNote={The residence time of subglacial meltwater impacts aquifer recharge, nutrient production, and chemical signals that reflect underlying bedrock/substrate, but is inaccessible to direct observation. Here we report the seasonal evolution of subglacial meltwater chemistry from the 2011 melt season at the terminus of the Athabasca Glacier, Canada. We measured major and trace analytes and U-series isotopes for twenty-nine bulk meltwater samples collected over the duration of the melt season. This dataset, which is the longest time-series record of (234U/238U) isotopes in a glacial meltwater system, provides insight into the hydrologic evolution of the subglacial system during active melting. Meltwater samples, measured from the outflow, were analyzed for (238U), (222Rn) and (234U/238U)activity, conductivity, alkalinity, pH and major cations. Subglacial meltwater varied in [238U] and (222Rn) from 23 to 832 ppt and 9 to 171 pCi/L, respectively. Activity ratios of (234U/238U) ranged from 1.003 to 1.040, with the highest (238U), (222Rn) and (234U/238U)activity values occurring in early May when delayed-flow basal meltwater composed a significant portion of the bulk melt. From the chemical evolution of the meltwater, we posit that the relative subglacial water residence times decrease over the course of the melt season. This decrease in qualitative residence time during active melt is consistent with prior field studies and model-predicted channel switching from a delayed, distributed network to a fast, channelized network flow. As such, our study provides support for linking U-series isotopes to storage lengths of meltwater beneath glacial systems as subglacial hydrologic networks evolve with increased melting and channel network efficiency.}, journal={CHEMICAL GEOLOGY}, author={Arendt, Carli A. and Aciego, Sarah M. and Sims, Kenneth W. W. and Aarons, Sarah M.}, year={2017}, month={Sep}, pages={42–52} }
 @article{niu_castro_hall_aciego_arendt_2017, title={Characterizing glacial meltwater sources in the Athabasca Glacier, Canada, using noble gases as tracers}, volume={76}, ISSN={0883-2927}, url={http://dx.doi.org/10.1016/J.APGEOCHEM.2016.11.015}, DOI={10.1016/J.APGEOCHEM.2016.11.015}, abstractNote={This study is the first comprehensive noble gas study in meltwater of an alpine glacier. It uses stable noble gases' (He, Ne, Ar, Kr, and Xe) concentrations and isotopic ratios from the Athabasca Glacier meltwater (AGMW), Canada, in an attempt to identify the original source location of ice melt and the relative contributions of modern surface melt versus basal melt and/or groundwater. It also estimates first order water residence times of the glacial meltwater (GMW) resulting from a mixture of modern surface and basal melt and/or groundwater. Two patterns are apparent with respect to noble gas concentrations: 1) a mass-dependent depletion pattern with stronger depletion of the heavier noble gases compared to the lighter ones, and 2) a pattern displaying a relative Ne depletion with respect to Ar. Ratios of noble gas concentrations suggest that different gases have different degrees of equilibration and samples are far from equilibration with the atmosphere at any temperature compatible with the glacial environment. Xe concentrations alone suggest that all AGMW samples equilibrated with the atmosphere at altitudes between 2500 m and 3400 m, altitudes that lie within the altitude range (1900 m–3500 m) of the Columbia Icefield. Most samples display Xe equilibration altitudes above the maximum altitude of the AG (∼2700 m), suggesting that a significant portion of the current AGMW originates in the Columbia Icefield which contributes to both the AG per se and current subglacial meltwater discharge. All AGMW samples are largely dominated by surface melt as opposed to basal melt with surface melt representing at least 71%–96% of the total GMW. Basal melt and/or groundwater represent at most 4%–29% of the total GMW. All AGMW samples exhibit tritiogenic 3He (3Hetrit) levels varying between 0 and 12 TU. Based on estimated 3Hetrit levels, 4He concentrations, and average U and Th concentrations in carbonates, we conclude that the bulk of our AGMW is likely a mixture between pre-bomb and present time GMW with a most likely average residence time of 160 ± 5 years with the exclusion of one present day sample.}, journal={Applied Geochemistry}, publisher={Elsevier BV}, author={Niu, Yi and Castro, M. Clara and Hall, Chris M. and Aciego, Sarah M. and Arendt, Carli A.}, year={2017}, month={Jan}, pages={136–147} }
 @article{arendt_stevenson_aciego_2016, title={Hydrologic controls on radiogenic Sr in meltwater from an alpine glacier system: Athabasca Glacier, Canada}, volume={69}, ISSN={0883-2927}, url={http://dx.doi.org/10.1016/J.APGEOCHEM.2016.04.002}, DOI={10.1016/J.APGEOCHEM.2016.04.002}, abstractNote={Filtered subglacial meltwater samples were collected daily during the onset of melt (May) and peak melt (July) over the 2011 melt season at the Athabasca Glacier (Alberta, Canada) and analyzed for strontium-87/strontium-86 (87Sr/86Sr) isotopic composition to infer the evolution of subglacial weathering processes. Both the underlying bedrock composition and subglacial water–rock interaction time are the primary influences on meltwater 87Sr/86Sr. The Athabasca Glacier is situated atop Middle Cambrian carbonate bedrock that also contains silicate minerals. The length of time that subglacial meltwater interacts with the underlying bedrock and substrate is a predominant determining factor in solute concentration. Over the course of the melt season, increasing trends in Ca/K and Ca/Mg correspond to overall decreasing trends in 87Sr/86Sr, which indicate a shift in weathering processes from the presence of silicate weathering to primarily carbonate weathering. Early in the melt season, rates of carbonate dissolution slow as meltwater approaches saturation with respect to calcite and dolomite, corresponding to an increase in silicate weathering that includes Sr-rich silicate minerals, and an increase in meltwater 87Sr/86Sr. However, carbonate minerals are preferentially weathered in unsaturated waters. During the warmest part of a melt season the discharged meltwater is under saturated, causing an increase in carbonate weathering and a decrease in the radiogenic Sr signal. Likewise, larger fraction contributions of meltwater from glacial ice corresponds to lower 87Sr/86Sr values, as the meltwater has lower water–rock interaction times in the subglacial system. These results indicate that although weathering of Sr-containing silicate minerals occurs in carbonate dominated glaciated terrains, the continual contribution of new meltwater permits the carbonate weathering signal to dominate.}, journal={Applied Geochemistry}, publisher={Elsevier BV}, author={Arendt, C.A. and Stevenson, E.I. and Aciego, S.M.}, year={2016}, month={Jun}, pages={42–49} }
 @article{clinger_aciego_stevenson_arendt_robbins_2016, title={Implications for post-comminution processes in subglacial suspended sediment using coupled radiogenic strontium and neodymium isotopes}, volume={259}, ISSN={0169-555X}, url={http://dx.doi.org/10.1016/J.GEOMORPH.2016.02.006}, DOI={10.1016/J.GEOMORPH.2016.02.006}, abstractNote={Enhanced physical weathering rates in subglacial systems promote high levels of comminution, transport, and deposition of fine-grained sediment within the subglacial drainage network. The impact of shifts in sediment loads from variations in meltwater flux, and their effects on downstream ecosystems, remains poorly quantified and places a fundamental importance on our ability to characterize subglacial depositional environments. Here, for the first time, we assess the seasonal evolution of the subglacial suspended sediment using coupled radiogenic strontium (87Sr/86Sr) and neodymium (143Nd/144Nd) isotopic ratios with elemental ratios and in situ measurements. Weathering rates in fluvial and riverine systems have been traditionally assessed using radiogenic isotopic tracers: 143Nd/144Nd ratios relate to the crustal age whereas 87Sr/86Sr ratios relate to age and preferential mineral dissolution. Thus relative shifts in these ratios will allow us to characterize distinct sediment transport networks. We apply this technique to the Lemon Creek Glacier (LCG), Alaska, USA, and to the Athabasca Glacier (AG), Alberta, CA. At the LCG, the 143Nd/144Nd values range from εNd of − 4.6 (0.9) to − 8.7 (0.2), which suggests a poorly mixed sediment flux. However, the greatest period of variability may correlate with the drainage of a supraglacial lake and suggests caution should be exerted in time-scale 143Nd/144Nd provenance studies that may be affected by climatic disturbances. In contrast, limited variation is observed within the AG 143Nd/144Nd seasonal record. A consistent, direct relation between the Rb/Sr elemental ratio and the 87Sr/86Sr ratio proves interesting as it enables us to unravel incongruent weathering trends in the radiogenic Sr record. Correlation between the 87Sr/86Sr and total discharge suggests that the process is partially controlled by mantling of the bedrock, which can be detected using post-comminution ages. While the subglacial structure may be enabled by the subglacial till beneath the AG, our study supports the use of Sr-Nd as a new proxy in the subglacial environment.}, journal={Geomorphology}, publisher={Elsevier BV}, author={Clinger, Anna E. and Aciego, Sarah M. and Stevenson, Emily I. and Arendt, Carli A. and Robbins, Mark J.}, year={2016}, month={Apr}, pages={134–144} }
 @article{stevenson_aciego_chutcharavan_parkinson_burton_blakowski_arendt_2016, title={Insights into combined radiogenic and stable strontium isotopes as tracers for weathering processes in subglacial environments}, volume={429}, ISSN={0009-2541}, url={http://dx.doi.org/10.1016/J.CHEMGEO.2016.03.008}, DOI={10.1016/J.CHEMGEO.2016.03.008}, abstractNote={This study reports stable and radiogenic strontium isotope behaviour in the dissolved load and suspended sediments from the subglacial outflow of the Lemon Creek glacier (Juneau Ice Field, Alaska) over a single melt season. In situ measurements (discharge, total alkalinity, pH and conductivity) are combined with elemental concentrations, X-ray diffraction (XRD) analysis and radiogenic strontium isotope measurements to interpret the variations observed in stable strontium isotopic ratios. The stable Sr isotope composition (88Sr/86Sr ratio expressed as δ88/86Sr, ‰) of the dissolved load averages 0.31 ± 0.05‰, and is heavier than both the suspended sediment 0.18 ± 0.03‰, as well as local bedrocks ~ 0.20 to 0.26‰. We attribute the enrichment of heavier isotopes in the dissolved load to the uptake of lighter Sr isotopes by secondary weathering minerals, driving the dissolved load to heavier values. X-ray diffraction (XRD) analysis confirms the presence of clays in the suspended sediments and thermodynamic modelling suggests the presence of iron oxy-hydroxide phases. Although it is not possible to completely rule out the effect of dissolution of primary minerals in controlling Sr isotopic compositions of the dissolved load, our data indicate that the extent of secondary mineral formation likely plays a significant role. The preferential weathering of minerals such as biotite (consistent with the mineralogical assemblages found in the suspended sediments), as well as the potential presence of radiogenic calcites from metacarbonates (derived from the Yukon-Tanana terrain), may be driving the small seasonal shifts in 87Sr/86Sr of the dissolved load to more radiogenic compositions, from 87Sr/86Sr(DL) = 0.71048 to 0.710647. Using the combination of stable and radiogenic strontium isotopes to investigate weathering processes shows that radiogenic Sr isotopes provide information regarding weathering of primary phases. While the stable Sr isotope data appear to record information regarding the extent of secondary mineral formation, where secondary minerals incorporate the light isotopes, driving the dissolved load to heavy values.}, journal={Chemical Geology}, publisher={Elsevier BV}, author={Stevenson, E.I. and Aciego, S.M. and Chutcharavan, P. and Parkinson, I.J. and Burton, K.W. and Blakowski, M.A. and Arendt, C.A.}, year={2016}, month={Jul}, pages={33–43} }
 @article{arendt_aciego_hetland_2015, title={An open source Bayesian Monte Carlo isotope mixing model with applications in Earth surface processes}, volume={16}, ISSN={1525-2027}, url={http://dx.doi.org/10.1002/2014GC005683}, DOI={10.1002/2014GC005683}, abstractNote={AbstractThe implementation of isotopic tracers as constraints on source contributions has become increasingly relevant to understanding Earth surface processes. Interpretation of these isotopic tracers has become more accessible with the development of Bayesian Monte Carlo (BMC) mixing models, which allow uncertainty in mixing end‐members and provide methodology for systems with multicomponent mixing. This study presents an open source multiple isotope BMC mixing model that is applicable to Earth surface environments with sources exhibiting distinct end‐member isotopic signatures. Our model is first applied to new δ18O and δD measurements from the Athabasca Glacier, which showed expected seasonal melt evolution trends and vigorously assessed the statistical relevance of the resulting fraction estimations. To highlight the broad applicability of our model to a variety of Earth surface environments and relevant isotopic systems, we expand our model to two additional case studies: deriving melt sources from δ18O, δD, and 222Rn measurements of Greenland Ice Sheet bulk water samples and assessing nutrient sources from ɛNd and 87Sr/86Sr measurements of Hawaiian soil cores. The model produces results for the Greenland Ice Sheet and Hawaiian soil data sets that are consistent with the originally published fractional contribution estimates. The advantage of this method is that it quantifies the error induced by variability in the end‐member compositions, unrealized by the models previously applied to the above case studies. Results from all three case studies demonstrate the broad applicability of this statistical BMC isotopic mixing model for estimating source contribution fractions in a variety of Earth surface systems.}, number={5}, journal={Geochemistry, Geophysics, Geosystems}, publisher={American Geophysical Union (AGU)}, author={Arendt, Carli A. and Aciego, Sarah M. and Hetland, Eric A.}, year={2015}, month={May}, pages={1274–1292} }
 @article{aciego_stevenson_arendt_2015, title={Climate versus geological controls on glacial meltwater micronutrient production in southern Greenland}, volume={424}, ISSN={0012-821X}, url={http://dx.doi.org/10.1016/J.EPSL.2015.05.017}, DOI={10.1016/J.EPSL.2015.05.017}, abstractNote={Low concentrations of micronutrients in subarctic North Atlantic surface waters limit phytoplankton growth. Iron, phosphorous, and silicon are all potentially bio-limiting nutrients; iron is the most well documented in the subarctic North Atlantic. Manganese, nickel, copper and zinc are also essential trace metals for phytoplankton cell function. However, the spatial and temporal variability in the flux of these elements to the subarctic North Atlantic is undercharacterized. Here we show new data from the meltseason peak in 2013 indicating that glacial meltwater from the southern tip of Greenland has elevated dissolved major and trace metal concentrations compared to glacial meltwater draining shorter melt season glacial catchments to the north. Fe concentrations range from 0.13 to 6.97 μM, Zn from 4 to 95 μM, and Si from 4 to 36 μM, all higher than the depleted surface waters of the subarctic North Atlantic. Measured hydrochemical data modeled by PHREEQC indicates meltwater is undersaturated in pyrite and silicate phases but supersaturated with respect to oxyhydroxides, hematite and goethite, all phases that precipitate Fe as colloids, of which the nanoparticle phases should remain biologically available. The variability in geologic units between the sites indicates that subglacial lithology is a minor but not the dominant control on meltwater chemistry. The disparity in concentrations is directly correlated with climate, and an extended melt season, suggesting that future warming in Greenland will lead to increased trace element, and potential micronutrient, flux to the subarctic North Atlantic surface waters.}, journal={Earth and Planetary Science Letters}, publisher={Elsevier BV}, author={Aciego, S.M. and Stevenson, E.I. and Arendt, C.A.}, year={2015}, month={Aug}, pages={51–58} }
 @article{niu_castro_aciego_hall_stevenson_arendt_das_2015, title={Noble gas signatures in Greenland: Tracing glacial meltwater sources}, volume={42}, ISSN={0094-8276}, url={http://dx.doi.org/10.1002/2015GL065778}, DOI={10.1002/2015GL065778}, abstractNote={AbstractThis study represents the first comprehensive noble gas study in glacial meltwater from the Greenland Ice Sheet. It shows that most samples are in disequilibrium with surface collection conditions. A preliminary Ne and Xe analysis suggests that about half of the samples equilibrated at a temperature of ~0°C and altitudes between 1000 m and 2000 m, with a few samples pointing to lower equilibration altitudes and temperatures between 2°C and 5°C. Two samples suggest an origin as melted ice and complete lack of equilibration with surface conditions. A helium component analysis suggests that this glacial meltwater was isolated from the atmosphere prior to the 1950s, with most samples yielding residence times ≤ 420 years. Most samples represent a mixture between a dominant atmospheric component originating as precipitation and basal meltwater or groundwater, which has accumulated crustal 4He over time.}, number={21}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Niu, Yi and Castro, M. Clara and Aciego, Sarah M. and Hall, Chris M. and Stevenson, Emily I. and Arendt, Carli A. and Das, Sarah B.}, year={2015}, month={Nov}, pages={9311–9318} }