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 2009
Description:
Estimates of natural climate variability during the past millennium provide a
frame of reference in which to assess the significance of recent changes. This thesis
investigates new methods of reconstructing low-latitude sea surface temperature (SST)
and hydrography, and combines these methods with traditional techniques to improve the
present understanding of western North Atlantic climate variability. A new
strontium/calcium (Sr/Ca) - SST calibration is derived for Atlantic Montastrea corals.
This calibration shows that Montastrea Sr/Ca is a promising SST proxy if the effect of
coral growth is considered. Further analyses of coral growth using Computed Axial
Tomography (CAT) imaging indicate growth in Siderastrea corals varies inversely with
SST on interannual timescales. A 440-year reconstruction of low-latitude western North
Atlantic SST based on this relationship suggests the largest cooling of the last few
centuries occurred from ~1650-1730 A.D., and was ~1ºC cooler than today. Sporadic
multidecadal variability in this record is inconsistent with evidence for a persistent 65-80
year North Atlantic SST oscillation. Volcanic and anthropogenic radiative forcing are
identified as important sources of externally-forced SST variability, with the latter
accounting for most of the 20th century warming trend. An 1800-year reconstruction of
SST and hydrography near the Gulf Stream also suggests SSTs remained within about
1ºC of modern values. This cooling is small relative to other regional proxy records and
may reflect the influence of internal oceanic and atmospheric circulation. Simulations
with an atmospheric general circulation model (AGCM) indicate that the magnitude of
cooling estimated by proxy records is consistent with tropical hydrologic proxy records.
Description:
Funding for this research was provided by a National Science Foundation Graduate
Student Fellowship, National Science Foundation grants OCE-0402728, OCE-0623364,
ATM-033746, the WHOI Ocean and Climate Change Institute, the WHOI Ocean
Ventures Fund, the WHOI Ocean Life Institute, the MIT Student Assistance Fund, award
number USA-0002, made by King Abdullah University of Science and Technology
(KAUST), and the Inter-American Institute for Global Change Research.
Keywords:
Ocean-atmosphere interaction
;
Climatic changes
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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