Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology
and the Woods Hole Oceanographic Institution September, 2005
Description:
This thesis evaluates the nature and magnitude of tropical climate variability from the
Last Glacial Maximum to the present. The temporal variability of two specific tropical
climate phenomena is examined. The first is the position of the Intertropical Convergence
Zone (ITCZ) in the Atlantic basin, which affects sea surface temperature (SST) and precipitation
patterns throughout the tropical Atlantic. The second is the strength of the Indian
Monsoon, an important component of both tropical and global climate.
Long-term variations in the position of the ITCZ in the Atlantic region are determined
using both organic geochemical techniques and climate modeling. Upwelling in Cariaco
Basin is reconstructed using chlorin steryl esters as proxies for phytoplankton community
structure. We find that the diatom population was larger during the Younger Dryas cold
event, indicating that upwelling was enhanced and the mean position of the ITCZ was
farther south during the Younger Dryas than it is today. A climate simulation using an
ocean-atmosphere general circulation model confirms these results by demonstrating that
the ITCZ shifts southward in response to high-latitude cooling.
The climate of the Arabian Sea region is dominated by the Indian Monsoon. Results
from modem sediments from a suite of cores located throughout the Arabian Sea suggest
that wind strength is well represented by the accumulation rate and carbon isotopic composition
of terrestrially-derived plant waxes in sediments. Arabian Sea SST patterns, reconstructed
from a suite of sediment cores representing four time slices utilizing the Mg/Ca
SST proxy, suggest that both the summer and winter monsoons were enhanced 8,000 yr BP
relative to today while the summer monsoon was weaker and the winter monsoon stronger
at 15,000 and 20,000 yr. These results are confirmed by a time-series reconstruction of SST
on the Oman Margin that reveals that SST at this site is sensitive to both regional and global
climate processes. The results of this thesis demonstrate that tropical climate, as evaluated
by a number of different proxies as well as climate models, has varied substantially over
the past 20,000 years and is closely coupled to climate at high-latitudes.
Description:
This work was funded by the National Science Foundation (OCE02-20776 and OCE0334598
to D. Oppo), a Schlanger Ocean Drilling Program Fellowship, a WHOI Watson
Fellowship, and a Fye Teaching Fellowship.
Keywords:
Marine sediments
;
Chemical elements
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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