Intra‐Valve Elemental Distributions in Arctic Marine Ostracodes: Implications for Mg/Ca and Sr/Ca Paleothermometry

Abstract

Reconstructing intermediate and bottom‐water temperature in the Arctic Ocean is key for understanding paleoclimatic phenomena, such as the region's interactions with warm Atlantic waters, stratification, and sea‐ice dynamics. However, benthic proxy archives are sparse throughout the Arctic circle compared to lower latitudes. Trace‐element ratios (E/Ca) derived from ostracodes, a group of bivalved microscopic crustaceans, have shown promise in this regard. Samples for E/Ca measurements typically require rigorous cleaning prior to analysis, and signs of contamination are routinely monitored through the presence of other trace elements such as Al, Fe, and Mn, which are associated with suspected sources of overprinting. However, there has not yet been an intra‐valve investigation of all of these trace elements, which may hinder our ability to effectively identify geochemical overprinting. Here, we present several elemental concentration and E/Ca ratio measurements in two ostracode genera, Krithe and Polycope, extracted from Chukchi Sea sediment samples. We further investigate the intra‐valve distribution of elements within single shells of adult and juvenile specimens using electron probe microanalysis (EPMA). Our findings suggest that brushing and bleach treatments may not be effective for completely eliminating clays from the edges of valves, which can bias paleoclimatologically relevant trace‐element proxies such as Mg/Ca ratios, particularly in the case of incomplete or small samples with low amounts of calcite material. In addition, we report the first trace‐element data from the genus Polycope, which shows potential as a new Arctic paleotemperature archive.

Calibration of Mg ∕ Ca and Sr ∕ Ca in coastal marine ostracods as a proxy for temperature

“…Element / calcium ratios (E/Ca) of secreted biogenic calcium carbonate by marine organisms, such as foraminifera and corals, have been used as proxies for past environmental marine parameters (Hendy et al, 2002;Lea, 2003;Lea and Boyle, 1989;Linsley et al, 2000;Martin et al, 2002). Mg/Ca in foraminifera and Sr/Ca in corals have been frequently used to reconstruct water temperatures (Beck et al, 1992;Cohen et al, 2001Cohen et al, , 2002Lea, 2003;Rosenthal et al, 2006;Sinclair et al, 1998;Yu and Elderfield, 2008). In addition, Mg/Ca of ostracod shells has also provided valuable information about water temperatures (Chivas et al, 1983(Chivas et al, , 1986aDe Deckker and Forester, 1988;Dwyer et al, 2002).…”