TOWARD A RELIABLE PROXY FOR PALEOSALINITY IN BAHAMIAN LAKE SYSTEMS: FACTORS AFFECTING THE MORPHOLOGY AND VALVE COMPOSITION OF CYPRIDEIS AMERICANA (OSTRACODA)

Ostracodes (bi-valved microcrustaceans) are well known for preserving chemical and morphological features (proxies) that can be linked to lake water temperature and salinity. This study analyzed the response of the euryhaline ostracode, Cyprideis americana, to salinity in six lakes from two Bahamian islands across two seasons. The purpose of this work was to determine which compositional and morphological variables in C. americana are the most useful for paleosalinity reconstructions.

Ostracode and water samples were collected from lakes of varying water chemistry on San Salvador Island (winter and summer seasons), and Exuma (winter season). Dissolved oxygen, pH, salinity, and temperature measurements were taken for each lake. Valves were analyzed for sieve pore circularity, Mg and Ca concentrations, and δ18 O isotopic composition. Mg/Ca ratios and Kd[Mg] values were calculated for each lake.

Only the samples collected during the summer followed expected trends: with increases in lake water salinity, Mg/Ca ratio decreased, δ18 O composition increased, and sieve pore circularity decreased. Samples collected from the winter field sessions did not follow expected trends, potentially due to the breeding and moulting habits of C. americana. Temperature was more correlative with valve composition than a previous study of C. americana suggests, but is supportive of similar correlations of Cyprideis species in continental and other island settings. The valve Mg/Ca ratio and mean sieve pore circularity showed the best correlation with salinity and are the variables that will be most useful in paleosalinity studies from sediment cores.