SALINITY VARIATION IN DUMP LAKE, RUM CAY, BAHAMAS OVER THE LAST MILLENNIUM

Records of past hydroclimate are critical to establishing baselines by which the magnitude of current anthropogenic climate change can be assessed. Past salinity of lakes on Rum Cay, Bahamas is determined by the frequency of hurricanes- times of fewer hurricanes corresponds to elevated salinity, whereas periods characterized by higher frequency of hurricanes corresponds to lowered salinity. We created a transfer function to convert preserved ostracode assemblages from a sediment core from Dump Lake on Rum Cay, Bahamas to past salinity to determine how past tropical storm activity affected lakes on Rum Cay.

We analyzed thirty-two sediment modern assemblages from lakes on Rum Cay for ostraocode species abundances as well as six environmental factors: electrical conductivity (salinity), dissolved oxygen, alkalinity, water temperature, pH, oxidation-reduction potential. We found that ostracode assemblages changed uniquely and independently with variation in conductivity. Therefore, we created a transfer function to express preserved ostracode assemblages in terms of past conductivity, with an r² of 48.8% when predicting the conductivity of other sites using a leave-one-out method.

We then applied this transfer function to sedimentary archives from the last ~1,000 years from Dump Lake on Rum Cay. With preliminary radiocarbon dating of leaves and other allochtonous material in the sediments preserved from Rum Cay, we find that times of strong El Niños correspond to elevated salinity in Dump Lake. This is caused by a reduction in hurricanes and tropical storms hitting Rum Cay, and thus delivering fresh water to lower the salinity of Dump Lake, during times of strong El Niños. Strong El Niños cause high upper altitude wind shear across the tropical Atlantic, inhibiting the formation of tropical storms that would deliver fresh water to Dump Lake. These results indicate environmental planners on Rum Cay should implement water conservation efforts during years in which strong El Niños are predicted in preparation for a potential drought.