OSTRACODE MG/CA PALEOTHERMOMETRY: APPLICATIONS TO PALEOCEANOGRAPHY

Understanding Cenozoic climate change at all timescales requires improved geochemical proxy methods to reconstruct sea-surface and bottom water temperature (BWT), pH, sea-ice, atmospheric pCO₂ and sea-level history from sediment records. The shell geochemistry of calcitic microfossils, particularly Mg/Ca ratios, is increasingly used in such studies as paleothermometers. Although shell chemistry of planktonic and benthic foraminifera have received substantial attention, marine ostracodes have several distinct advantages for BWT reconstruction: long stratigraphic ranges for well-studied genera (Krithe, Loxonconcha: Cretaceous-Recent), growth by molting (no ontogenic variability with adult shell analyses), large heavily calcified shells (0.3-1.0 mm; 10-100 µg), and high Mg/Ca concentrations over wide temperature ranges (Loxoconcha 10-26˚C, 20-50 mmol/mol; Krithe: -1.5 to 14˚C, 5 to 25 mmol/mol). In addition, some deep-sea species of Krithe may live infaunally (~1 to 10 mm), reducing the influence of carbonate saturation state that complicates deep benthic epifaunal foraminifera like Cibicidoides. We will present Mg/Ca records from the Pliocene-Quaternary of the North Atlantic, the last 50 ka from the Arctic, and the Holocene of Chesapeake Bay and focus on issues of past and current climatic warming and ocean circulation.