Ecology of the past

Earlier this month Rachel Gwynn (Geography, UCL) visited the PCRG to use our core splitter to reveal what was contained within two cores collected from the Carribean. She has also been kind enough to provide photos of the sediments and an insight into the story so far:

Sediments from Fresh Water Pond Barbuda (Photograph Rachel Gwynn)

Lake sediment cores covering the past few hundred to thousand years have been taken from two lakes, Wallywash Great Pond in Jamaica and Freshwater Pond in Barbuda. The sediments form part of the NERC-funded project Neotropics1k (PI Prof. Jonathan Holmes), which is concerned with climate variability in the northern Neotropics over the past millennium. The sediment cores show marked changes in composition and colour, from pale marl to dark organic mud. These colour changes, which are clearly visible in the photographs, represent changes in sediment composition that are in turn related to lake-level variations caused by long-term climate shifts. Deeper, open-water conditions under wetter climate are represented by the marls, whereas lowered lake levels, caused by direr climate, are associated with organic-rich sediments.

Wallywash Great Pond– core section W2

• Thirteen separate units have been identified through the 1 m core length, varying between light coloured marl, dark organic and shelly sediments.
• The abundance of preserved Ostracod valves increases throughout the marl and shell rich layers but drops significantly in the organic rich material.

Barbuda Freshwater Pond- core section FWP

• This core has four distinct units. 0-23 cm is a calcareous mud with a diffused lower boundary into a shelly calcareous mud at 25-35.5 cm. 35.5-38 cm and 38-52 cm is two variations of calcareous mud.
• These units, as with the W2 core, have been defined using a Munsel Soil Chart.
• The Ostracod valves are thought to be abundant throughout the core due to the high marl content.

Wallywash Great Pond Jamaica (photograph Rachel Gwynn)