Mg/Ca ratios in ostracode genera Sarsicytheridea and Paracyprideis: A potential paleotemperature proxy for Arctic and subarctic continental shelf and slope waters

Abstract

We evaluate the potential utility of Mg/Ca in the ostracode genera Sarsicytheridea and Paracyprideis as a paleotemperature proxy for continental shelf and upper slope waters of the Arctic Ocean and adjacent seas. Using sediment core-top and surface sediment samples, shells of three species, S. bradii, S. punctillata, and P. pseudopunctillata, were analyzed from Arctic Ocean sites in water depth from 7 to 200 m and bottom-water temperatures (BWT) of −1.5 °C to 12 °C. Mg/Ca values range from 4 to 9 mmol/mol. These results are in excellent agreement with the range of Mg/Ca obtained in a previous study (Ingram, 1998) of shells of Sarsicytheridea from the sub-polar North Atlantic Ocean region with BWT ranging from 1 to 11.4 °C. Unlike this study of Sarsicytheridea, and work on the Arctic ostracode marine genus Krithe showing strong correlations between Mg/Ca and BWT, analysis of Mg/Ca in this study are not correlated with BWT below 0 °C. We hypothesize that this primarily has to do with uncertainty regarding the actual ambient BWT at the time of shell secretion. As with many continental shelf sites, individual sites used in the study have large interannual and seasonal variations in BWT (≥5–8 °C). Thus, there is difficulty in assigning a shell secretion temperature and assessing the utility of Sarsicytheridea Mg/Ca ratios as a paleotemperature proxy below 0 °C. The calibration of Mg/Ca results from temperatures above 0 °C justifies continued evaluation of this potential paleothermometer for Arctic continental shelf and upper slope environments.