Use of Me/Ca ratios as proxies for coastal marine conditions in ostracod shells of Sinocytheridea impressa and Neomonoceratina delicata

Abstract

Paleo-reconstructions using element to calcium ratios (Me/Ca) of marine ostracods were usually focused on Mg/Ca and Sr/Ca, whereas paleo-environmental applications using other ostracod Me/Ca including Na/Ca, Ba/Ca, Mn/Ca, Zn/Ca, Ni/Ca, Cd/Ca, Cu/Ca and Cr/Ca have been rather limited due to the lack of a general understanding of the control of physicochemical marine variables on trace-elements uptake. Ba/Ca and Na/Ca were linked to temperature, while Mn/Ca was suggested to be an indicator of redox conditions and used to track oxide contamination in marine shells. The potential of other ostracod ratios as environmental proxies has rarely been investigated. Here, we study the empirical relations between seawater physicochemical variables and several Me/Ca of ostracod shells in shallow marine waters. Our results suggest that shallow sea parameters related to the control of metal concentrations in seawater and sediments such as suspended solids, salinity, electrochemical potential and total carbon are correlated to Me/Ca such as Mn/Ca and Zn/Ca in ostracod shells of Sinocytheridea impressa and Neomonoceratina delicata from Hong Kong coastal waters. Correlations are not always significant for both species, indicating that other factors such as species-specific habitats or biomineralization processes may also play a role in the incorporation of metals. We demonstrate that the combination of multiple linear regressions using several significant sea parameters provides useful information to reconstruct shallow marine conditions including water temperature, salinity, suspended solid and total carbon in sediments. Thus, a detailed description of the marine environment in Hong Kong coastal waters can be achieved.