Gibbons Fern T.
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ArticleDeglacial δ18O and hydrologic variability in the tropical Pacific and Indian Oceans(Elsevier, 2013-11) Gibbons, Fern T. ; Oppo, Delia W. ; Mohtadi, Mahyar ; Rosenthal, Yair ; Cheng, Jun ; Liu, Zhengyu ; Linsley, Braddock K.Evidence from geologic archives suggests that there were large changes in the tropical hydrologic cycle associated with the two prominent northern hemisphere deglacial cooling events, Heinrich Stadial 1 (HS1; ∼19 to 15 kyr BP; kyr BP = 1000 yr before present) and the Younger Dryas (∼12.9 to 11.7 kyr BP). These hydrologic shifts have been alternatively attributed to high and low latitude origin. Here, we present a new record of hydrologic variability based on planktic foraminifera-derived δ18O of seawater (δ18Osw) estimates from a sediment core from the tropical Eastern Indian Ocean, and using 12 additional δ18Osw records, construct a single record of the dominant mode of tropical Eastern Equatorial Pacific and Indo-Pacific Warm Pool (IPWP) hydrologic variability. We show that deglacial hydrologic shifts parallel variations in the reconstructed interhemispheric temperature gradient, suggesting a strong response to variations in the Atlantic Meridional Overturning Circulation and the attendant heat redistribution. A transient model simulation of the last deglaciation suggests that hydrologic changes, including a southward shift in the Intertropical Convergence Zone (ITCZ) which likely occurred during these northern hemisphere cold events, coupled with oceanic advection and mixing, resulted in increased salinity in the Indonesian region of the IPWP and the eastern tropical Pacific, which is recorded by the δ18Osw proxy. Based on our observations and modeling results we suggest the interhemispheric temperature gradient directly controls the tropical hydrologic cycle on these time scales, which in turn mediates poleward atmospheric heat transport.
ThesisThe centennial and millennial variability of the IndoPacific Warm Pool and the Indonesian Throughflow(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2012-02) Gibbons, Fern T.As the only low-latitude connection between ocean basins, the Indonesian Throughflow allows the direct transmission of heat and salinity between the Pacific and Indian Oceans. The Mg/Ca and δ18O of calcite of Globigerinoides ruber (G. ruber) were used to estimate the sea surface temperature (SST) and δ18O of water, an indicator of hydrologic conditions, over the past 20,000 years. I also attempted to estimate thermocline structure using Pulleniatina obliquiloculata, but the Mg/Ca and δ18O of calcite data yield conflicting interpretations, indicating further work on this proxy is required. The G. ruber Mg/Ca results suggest that the SST of the outflow passages were influenced by high latitude Southern Hemisphere temperature. At approximately 10,000 years before present, there was a warming in the Makassar Strait. This local warming was coincident with the flooding of the Sunda Shelf, which opened a connection between the South China Sea and the Indonesian Throughflow. Regional δ18O of seawater reconstructions suggest that the mean position of the Intertropical Convergence Zone (ITCZ) was approximately the same as modern at the last glacial maximum and was displaced to the south during the Younger Dryas and Heinrich Stadial 1, suggesting the ITCZ responds to changes in the interhemispheric temperature gradient.