ASSESSING THE FEASIBILITY OF STABLE OXYGEN ISOTOPES FROM OSTRACODE SHELLS AS PALEOCEANOGRAPHIC PROXIES FOR WATER MASS IN ARCTIC AND SUBARCTIC CONTINENTAL SHELF ENVIRONMENTS

Measurements of stable oxygen isotopes on calcitic valves of benthic ostracodes (δ¹⁸O_ost) from the northern Bering and Chukchi Seas were used to examine ecological and hydrographic processes influencing ostracode and associated seawater δ¹⁸O values. Five cryophilic taxa were analyzed for δ¹⁸O_ost values: Sarsicytheridea bradii; Paracyprideis pseudopunctillata; Heterocyprideis sorbyana; Heterocyprideis fascis; and the subarctic species Normanicythere leioderma. Controls on the stable oxygen isotope composition of ostracode calcite were investigated by first establishing species’ vital effects and then comparing ostracode δ¹⁸O to seawater δ¹⁸O values (that ranged from -2.7 to -0.5‰), CTD temperature (-1.7 to 8.7°C) and salinity (30-34) measured at sampling stations in the Bering and Chukchi Seas during the six summers of 2013-2018. Results from 297 δ¹⁸O_ost measurements from 53 sites on the Bering and Chukchi Sea continental shelves are consistent with the temporal and spatial variation in δ¹⁸O values of continental shelf bottom water, as impacted by seasonality, regional hydrography, and physical processes (i.e., sea-ice melt and extent, vertical mixing, precipitation/evaporation). Regression statistics for δ¹⁸O_ost values of two species showed correlations to temperature and salinity that may facilitate prediction of water-mass characteristics when applied to sediment core records. Specifically, a significant linear regression relationship was found between δ¹⁸O_ostvalues of N. leioderma and P. pseudopunctillata and temperature (R² = 0.67 and 0.52, respectively). A principal component analysis confirmed temperature as the main controlling factor in the δ¹⁸O_ost values of all species except S. bradii, with samples of distinct water masses grouping together.