@article{wojtal_doherty_shea_popp_benitez-nelson_buesseler_estapa_roca-marti_close_2023, title={Deconvolving mechanisms of particle flux attenuation using nitrogen isotope analyses of amino acids}, ISSN={["1939-5590"]}, DOI={10.1002/lno.12398}, abstractNote={Particulate organic matter settling out of the euphotic zone is a major sink for atmospheric carbon dioxide and serves as a primary food source to mesopelagic food webs. Degradation of this organic matter encompasses a suite of mechanisms that attenuate flux, including heterotrophic metabolic processes of microbes and metazoans. The relative contributions of microbial and metazoan heterotrophy to flux attenuation, however, have been difficult to determine. We present results of compound specific nitrogen isotope analysis of amino acids of sinking particles from sediment traps and size-fractionated particles from in situ filtration between the surface and 500 m at Ocean Station Papa, collected during NASA EXPORTS (EXport Processes in the Ocean from RemoTe Sensing). With increasing depth, we observe: (1) that, based on the δ15N values of threonine, fecal pellets dominate the sinking particle flux and that attenuation of downward particle flux occurs largely via disaggregation in the upper mesopelagic; (2) an increasing trophic position of particles in the upper water column, reflecting increasing heterotrophic contributions to the nitrogen pool and the loss of particles via remineralization; and (3) increasing δ15N values of source amino acids in submicron and small (1–6 μm) particles, reflecting microbial particle solubilization. We further employ a Bayesian mixing model to estimate the relative proportions of fecal pellets, phytodetritus, and microbially degraded material in particles and compare these results and our interpretations of flux attenuation mechanisms to other, independent methods used during EXPORTS.}, journal={LIMNOLOGY AND OCEANOGRAPHY}, author={Wojtal, Paul K. and Doherty, Shannon C. and Shea, Connor H. and Popp, Brian N. and Benitez-Nelson, Claudia R. and Buesseler, Ken O. and Estapa, Margaret L. and Roca-Marti, Montserrat and Close, Hilary G.}, year={2023}, month={Jul} }
 @article{davis_doherty_fehrenbacher_wishner_2023, title={Trace element composition of modern planktic foraminifera from an oxygen minimum zone: Potential proxies for an enigmatic environment}, volume={10}, ISSN={["2296-7745"]}, DOI={10.3389/fmars.2023.1145756}, abstractNote={Oxygen limited marine environments, such as oxygen minimum zones, are of profound importance for global nutrient cycling and vertical habitat availability. While it is understood that the extent and intensity of oxygen minimum zones are responsive to climate, the limited suite of viable proxies for low oxygen pelagic environments continues to pose a real barrier for paleoclimate interpretations. Here we investigate the proxy potential of an array of trace element (Mg, Mn, Zn, and Sr) to Ca ratios from the shells of Globorotaloides hexagonus , a planktic foraminifer endemic to tropical through temperate oxygen minimum zones. A species-specific relationship between Mg/Ca and temperature is proposed for quantitative reconstruction of oxygen minimum zone paleotemperatures. Both Mn/Ca and Zn/Ca ratios vary with oxygen concentration and could be useful for reconstructing G. hexagonus habitat where the primary signal can be d\istinguished from diagenetic overprinting. Finally, a robust correlation between Sr/Ca ratios and dissolved oxygen demonstrates a role for Sr as an indicator of oxygen minimum zone intensity, potentially via foraminiferal growth rate. The analysis of these relatively conventional trace element ratios in the shells of an oxygen minimum zone species has tremendous potential to facilitate multiproxy reconstructions from this enigmatic environment.}, journal={FRONTIERS IN MARINE SCIENCE}, author={Davis, Catherine V. and Doherty, Shannon and Fehrenbacher, Jennifer and Wishner, Karen}, year={2023}, month={Mar} }