Paleolimnological Analysis of Sediment Cores from Guana Island Pond, Guana Island, The British Virgin Islands

Abstract

Shallow sediment cores extracted from three locations in Guana Island Pond were analyzed using multiple paleolimnological techniques, including sediment description, grain size analyses, X-Ray Fluorescence, elemental analyses, scanning electron microscopy, and fossil identification. These data were used to define six depositional units (1-6) that mark the change in paleoenvironment of the lake. Two radiocarbon dates on organic material from 27 cm and 65 cm depth in the cores yielded calibrated ages of 720 ± 40 yr BP and 1307 ± 46 yr BP, respectively. Approximately 2200 yr BP, Guana Island Pond was likely a tidal estuary with sandy storm deposits. By 1500-900 yr BP, an abundance of Chara fibrosa oogonia (a freshwater algae) suggest the pond closed off from the sea and runoff exceeded evaporation in a regional wetter climate phase. At this time, the lake was possibly a viable source of potable fresh water for pre-Columbian native peoples and early European settlers. After about 900-700 yr BP, the lake alternated between marine to brackish to freshwater conditions. The uppermost layer of the lake sediment contains high levels of Fe, Ti, and Si indicating an increase in watershed erosion and soil runoff, likely from development of the island from the Quaker settlement period (18th century) through the 20th century.