Stable oxygen isotopes in shallow marine ostracodes from the northern Bering and Chukchi Seas

Stable oxygen isotope measurements on calcitic valves of benthic ostracodes (delta O-18(ost)) from the northern Bering and Chukchi Seas were used to examine ecological and hydrographic processes governing ostracode and associated seawater delta O-18 values. Five cryophilic taxa were analyzed for delta O-18(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 delta O-18(ost) to seawater delta O-18 values (that ranged from -2.7 to -0.5 parts per thousand), CTD temperature (-1.7 to 8.7 degrees 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 delta O-18(ost) measurements from 53 sites on the Bering and Chukchi Sea continental shelves are consistent with the temporal and spatial variation in delta O-18 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 delta O-18(ost) values of two species, N. leioderma and P. pseudopunctillata, 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 delta O-18(ost) values of N. leioderma and P. pseudopunctillata and temperature (R-2 = 0.67 and 0.52, respectively). A principal component analysis confirmed temperature as the main controlling factor in the delta O-18(ost) values of all species except S. bradii, with samples of distinct water masses grouping together. The delta O-18(ost) values of S. bradii exhibited a narrow range of values (similar to 3 to 4.5 parts per thousand) across a temperature range of 10 degrees C. Due to strong vital effects and possibly other undetermined factors, the incorporation of delta O-18(ost) in S. bradii was not driven by any obvious predominant environmental factors.

Automated summary

Stable oxygen isotope measurements on calcitic valves of benthic ostracodes were used to examine ecological and hydrographic processes governing ostracode and associated seawater values. The results showed that the stable oxygen isotope composition was influenced by seasonality, regional hydrography, and physical processes. The study also found correlations between stable oxygen isotope values of certain species and temperature and salinity, which can be used to predict water-mass characteristics.