Little Ice Age climate in the Western Tropical Atlantic inferred from coral geochemical proxies
MetadataShow full item record
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.
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
Suggested CitationThesis: 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/1912/8410
Showing items related by title, author, creator and subject.
Abrupt climate change in the Atlantic Ocean during the last 20,000 years : insights from multi-element analysis of benthic and planktic foraminifera and a coupled OA-GCM Came, Rosemarie E. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2005-09)Minor and trace element records from planktic and benthic foraminifera from Atlantic sediment cores, as well as outputfrom a coupled OA·GCM, were used to investigate the magnitude and distribution of the oceanic response ...
Fornace, Kyrstin L. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2016-02)Characterizing global and regional climate variability and climate-carbon cycle interactions in the past provides critical context for evaluating present and future climate trends. In this thesis, I use stable isotope ...
Geochemistry of slow-growing corals : reconstructing sea surface temperature, salinity and the North Atlantic Oscillation Goodkin, Nathalie F. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007-06)A 225-year old coral from the south shore of Bermuda (64°W, 32°N) provides a record of decadal-to-centennial scale climate variability. The coral was collected live, and sub-annual density bands seen in x-radiographs ...