Little Ice Age climate in the Western Tropical Atlantic inferred from coral geochemical proxies
Citable URI
https://hdl.handle.net/1912/8410DOI
10.1575/1912/8410Keyword
Climate changesAbstract
Paleoclimate archives place the short instrumental record of climate variability in
a longer temporal context and allow better understanding of the
rate,
nature
and
extent
by
which
anthropogenic
warming
will
impact
natural
and
human
systems. The ocean is a
key component of the climate system and records of past ocean variability are thus
essential for characterizing natural variability and quantifying climate sensitivity to
radiative forcing. Coral skeletons are high-resolution archives of tropical sea surface
temperatures (SSTs), but inconsistencies call the accuracy of existing coral proxy records
into question. In this thesis, I first quantify the errors associated with the traditional coral
thermometer, Sr/Ca, by comparing in situ logged SST with Sr/Ca-derived SST in four
corals on the same reef. I show that intercolony disparities in mean Sr/Ca, amplitude of
variability, and trend are not due to differences in water temperature, but rather to
“vital effects” that result in a ± 2 ̊C uncertainty on reconstructed SST.
I then expand, refine, and test a new paleothermometer, Sr-U, across multiple coral
species and through time. I show that Sr-U captures spatial SST variability with an
uncertainty of ± 0.6 ̊C. When applied to two corals outside of the calibration, Sr-U
accurately captures the mean SST and the 20th century trend in the Western Tropical
Atlantic.
Finally, I apply Sr-U to a coral from the Little Ice Age (LIA) to address uncertainties in
the magnitude of western tropical Atlantic cooling during a 95-year period spanning
1465-1560. Results suggest the region was 1.1 ̊C±0.6°C cooler than the 1958-1988 mean,
but within error of early 20th century SST at this site. Critically, several periods of
warmth, equivalent to the 1958-1988 mean, occurred during a solar minimum that is
widely believed to have been a cool period of the LIA. My results indicate that Sr/Ca
exaggerates the actual cooling by almost 3 °C. My record demonstrates the value of Sr-U
and highlights the need for continuous accurate SST records to better constrain the
amplitude, drivers, and mechanisms of LIA tropical climate change.
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 2016
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Suggested Citation
Thesis: Alpert, Alice, "Little Ice Age climate in the Western Tropical Atlantic inferred from coral geochemical proxies", 2016-09, DOI:10.1575/1912/8410, https://hdl.handle.net/1912/8410Related items
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