Title

Seasonal to centennial Holocene and modern climate variability in the Dominican Republic

Date of Award

2001

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Peter K. Swart, Committee Chair

Abstract

Holocene and Modern Montastraea sp. and Sidearastrea sp. corals were collected from the Dominican Republic to examine temporal and spatial changes in regional climate. Measurements of stable carbon (delta13C) and oxygen (delta18O) isotopic composition and linear coral extension rate were performed on all corals to examine potential changes in sea surface temperature (SST) and precipitation patterns with time. Ages of Holocene corals were determined by measurements of 234U/230Th isotopic ratios.Decadal oscillations in the delta18O of a Modern coral from Parque Nacional del Este (PNE) correlate with SST anomalies in the tropical North Atlantic with a dominant frequency of ∼12--15 years. Changes in the degree of correlation between SST anomalies and delta18O suggest a temporary nature to a hypothesized Tropical Atlantic SST Dipole. In contrast to data from the Modern coral, decadal to multi-decadal oscillations in the delta18O and delta13C of Holocene corals from the Enriquillo Valley show a dominant periodicity of ∼15--20 years. The proposed driving mechanism for decadal to multi-decadal Holocene cyclicity is the periodic passage of tropical storms and hurricanes over the Enriquillo Valley. During passage, anomalous precipitation may have changed the course of the Rio Yaque del Sur, flooding the paleo-Enriquillo embayment with fresh water, and significantly altering the isotopic composition of the embayment. Holocene tropical storm cyclicity may be linked to patterns in ENSO activity and precipitation in the West African Sahel, both of which may be mediated by tropical Atlantic SST variability.High-resolution delta13C and delta18O data from the Enriquillo corals may reflect a well-known decrease in Northern Hemisphere summer insolation during the Mid-Holocene. Geochemical data from corals show a decrease in the seasonal amplitude of delta18O from ∼7.2 to ∼5.2 ka. The decrease may reflect a dampening of thermal seasonality, or a decrease in the latitudinal extent of the Atlantic Intertropical Convergence Zone, as mediated by changing Holocene insolation. Shifts in the mean delta13C and delta18O of Holocene corals suggest the onset of a warm and/or wet period at ∼7 ka in the tropical Atlantic. The timing of this hypothesized climatic shift is in agreement with other proxy climate records from the region.Measurement of linear extension rates from 18 Modern corals from the southeastern Dominican Republic suggest the most potentially significant environmental factors governing annual extension may be temperature and tropical storm activity. The mean trend of coral extension increased in coincidence with rising regional SST's. These data do not support the hypothesis that rising atmospheric CO2 levels would result in decreased coral calcification.

Keywords

Physical Geography; Geology

Link to Full Text

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