Mg/Ca Ratios in Ostracode Genera Sarsicytheridea and Paracyprideis: A Potential Paleotemperature Proxy for Arctic and Sub-Arctic Continental Shelf and Slope Waters
Abstract
We evaluate the potential utility of Mg/Ca ratios in the sub-littoral ostracode genera Sarsicytheridea and Paracyprideis as a paleotemperature proxy for continental shelf and upper slope waters of the Arctic Ocean and adjacent seas. Sediment core-top and surface sediment shells of three species, S. bradii, S. punctillata, and P. pseudopunctillata were analyzed from Arctic Ocean sites ranging in water depth from 7 to 200 meters and bottom-water temperatures (BWT) of -1.5 °C to 12 °C. Generally, Mg/Ca ratios range from 4 to 9 mmol/mol, showing excellent agreement with the range of Mg/Ca ratios obtained in a previous study of core-top shells of Sarsicytheridea from sites in the sub-polar North Atlantic and adjacent seas with BWT ranging from 1 to 12 °C (Ingram, 1998, Quat. Sci. Reviews 17: 913). However, unlike the Ingram study on Sarsicytheridea, and previous work with the deep-sea and shallow Arctic ostracode genus Krithe, both of which show strong correlations between Mg/Ca and BWT, Mg/Ca ratios in the Arctic specimens analyzed in this study yield a weaker correlation with BWT, especially at temperatures below 0 °C. We hypothesize that this weak correlation has to do with uncertainty regarding the actual ambient BWT of the study sites at the time of shell secretion. As with many continental shelf sites, in the Arctic Ocean and throughout the World's oceans, the individual sites used in this study have large interannual and seasonal variations in BWT, in many cases spanning the full range of temperature for all of the sites studied. Thus, there is considerable difficulty in assigning a proper shell secretion temperature and, in turn, fully assessing the utility of Sarsicytheridea and Paracyprideis Mg/Ca ratios as a paleotemperature proxy. There are a number of possible solutions, such as laboratory culturing under controlled conditions, adding additional sites with a range of maximal and minimal bottom water temperatures, and pairing other geochemical or isotopic measures of temperature, among others. The collective results are encouraging and justify further evaluation of this potential paleothermometer for Arctic continental shelf and upper slope environments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP33A..06D
- Keywords:
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- 0424 Biosignatures and proxies;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES