242 Archaeological Geology (Posters)

Wednesday, 21 October 2009
9:00 AM - 6:00 PM
Hall A

ANTHROPOGENIC HEAVY METALS IN SEDIMENT CORES FROM SALT POND, SAN SALVADOR, THE BAHAMAS

Paper number: 242-17
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The lakes of San Salvador Island, Bahamas potentially contain important high-resolution records of environmental and climatic change. Lakes on the island vary in salinity, controlled by the degree of development of the marine conduit system, the presence of local fresh groundwater lenses, the size of the lake, its elevation relative to sea level, and rainfall. Salt Pond is a shallow hypersaline lake on the eastern side of the island. Four cores measuring from 21 cm to 76 cm in length were recovered from Salt Pond in January 2008. In the lab, the texture and composition of layers in the cores were described. Sediment was sampled every centimeter in the cores. The percentage of organic carbon, water content, and carbonate were measured using the Loss on Ignition (LOI) method. In order to determine the base of the historic period, trace element and heavy metal concentrations were measured using an Inductively Coupled Plasma Mass Spectrometer. One radiocarbon age determination on a plant fragment at a depth of 35 cm indicates it was deposited ca. 1200 years ago. Between 18 and 21 cm depth in the core, there is a sharp rise in arsenic concentration with a concomitant increase in tin, nickel, copper, zinc, cobalt, and cadmium levels. This contrasts with the upper 6 cm of surface sediment where these metals are present in high concentrations with an additional noted enrichment of lead, iron, and chromium. The increase concentration of the heavy metals are likely correlative to the historical periods on San Salvador that started when British loyalist fleeing the American colonies established plantations in the British-held Bahamas in the 1780s. Both zinc and cadmium were used as pigments in 18th century wares. Peak nickel, copper, and other metals that are not native to the local setting are indicators of anthropogenic input. These data shown that a linear extrapolation of sedimentation rate is not a good indication of the age versus depth relationship in the cores. Additional data on historical land use practices and comparisons to cores from other lakes are needed in order to better constrain the source and distribution of the metals.