Masters Theses

Date of Award

8-2007

Degree Type

Thesis

Degree Name

Master of Science

Major

Geography

Major Professor

Kenneth H. Orvis

Committee Members

Sally P. Horn, Henri D. Grissino-Mayer

Abstract

The paleoecological history of the Bahamas archipelago is one of change throughout the Holocene, and is recorded in the sediments deposited in solution holes. However, with its karstic pine rocklands landscape, Great Abaco Island has virtually no overland flow of water, neither rivers nor sheet-flow. This means that transport of charcoal produced through biomass burning and deposited in local ponds and solution holes is primarily microscopic in size and is probably transported by wind. Fires in the pine rocklands are mainly low-intensity ground fires that result in very little aerial transport of charcoal. Unless a fire occurs immediately adjacent to a pond, very little microscopic or macroscopic charcoal is deposited in it.

Split Pond, located in the northeast portion of Great Abaco Island, yielded a 2.7 m long core retrieved beneath 30 cm of water. A piece of charcoal recovered from near the base of the core has been dated to 5830 ± 50 14C yr BP. At approximately 250 cm in the core, there is a discontinuity in the sediments, with a layer of dense, clayey material below 230 cm abruptly changing to organic-laced marl above. This is possibly due to a period when the lake became completely dry, exposing the sediments to erosive processes. The 5830 ± 50 14C yr BP date was recovered from the dense clay layer, but because of the condition of the sediments, a full examination of material from this layer was not practical. Immediately above the discontinuity, at approximately 220 cm, material yielding a date of 1503 ± 37 14C yr BP was recovered, which serves as the basal date for the studied portion of the core. Two dates above the discontinuity (2910 ± 40 and 1152 ± 36 14C yr BP) are considered to be older, redeposited material and have been discussed as such.

Pollen preservation is poor throughout the core, with pine pollen, presumably of Pinus caribaea var. bahamensis, robust enough to be present in sufficient amounts to allow for counting, but even that is poorly preserved at certain levels possibly due to water alkalinity or periods of drying. Charcoal analysis of the core indicates a period of increased burning in the area of Split Pond ca. 1300 14C yr BP, which correlates with the suggested arrival time of the Lucayans in the Bahamas. In the upper portion of the core, the data indicate a prolonged period of increased burning since ca. 1000 14C yr BP. Pine pollen also increased during this period. In most levels of the core neither microscopic nor macroscopic charcoal fragments are found in abundance, a finding that fits with other paleoenvironmental studies conducted in the pine rocklands.

As a second portion of the study, samples of air-fall charcoal were collected in open Petri-dish traps during a controlled burn in the recently chartered Great Abaco National Park. The fire was a low-intensity ground fire type that most commonly occurs in the pine rocklands. For those traps placed down-wind of the burn, microscopic charcoal was deposited in significant amounts, but macroscopic charcoal was not found in quantity. The traps placed approximately 1 km upwind of the burn as controls yielded no charcoal of any size. This supports the hypothesis that the low intensity ground fires in the pine rocklands produce low amounts of microscopic charcoal that is wind-transported into local ponds, but are not intense enough to transport appreciable amounts of macroscopic charcoal. This helps explain the relatively low amounts of charcoal found in my Split Pond study and in other paleoecological studies conducted in the Bahamian archipelago.

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