Reconstructing hydrographic gradients and the carbon isotopic composition of surface waters using mu...

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" Reconstructing hydrographic gradients and the carbon isotopic composition of surface waters using multiple species of planktonic foraminifera "
J. S. Oslick W. L. Prell

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113321
Doc. No	:	TLpq304418115
Main Entry	:	J. S. Oslick
	:	W. L. Prell
Title & Author	:	Reconstructing hydrographic gradients and the carbon isotopic composition of surface waters using multiple species of planktonic foraminifera\ J. S. OslickW. L. Prell
College	:	Brown University
Date	:	1998
student score	:	1998
Degree	:	Ph.D.
Page No	:	210
Abstract	:	The accuracy of past climate estimates utilizing planktonic foraminifera is limited by our knowledge of their habitats, which determine the stable isotopic (usd\delta\spusdO, usd\delta\spusdC) signals carried by their tests. This study refines habitat estimates of the species Globigerinoides ruber, Globigerinoides sacculifer, and Globorotalia menardii, and applies these refined habitats to estimate the of near surface hydrography and water chemistry for the Last Glacial Maximum (LGM) Indian Ocean. Globigerinoides ruber was found to record mixed layer conditions in most locations. Globigerinoides sacculifer was found to regularly record upper-thermocline depths in many locations, inconsistent with its frequent use to estimate near-surface conditions. Globorotalia menardii consistently records conditions associated with the middle depths of the seasonal thermocline. A reconstruction of the Indian Ocean thermocline structure at the Last Glacial Maximum using the usd\Delta\delta\spusdO difference (G. menardii minus G. ruber or G. sacculifer) produced slight cooling of the eastern equatorial surface waters, with a substantial reduction in thermocline strength in the eastern and southeastern Indian Ocean. A slight warming of the Southern Indian Ocean gyre is inferred, which may contribute to warmer thermocline temperatures in the western Indian Ocean. The northwestern Arabian Sea data shows little change, while the northern Arabian Sea recorded an increased near-surface stratification associated with a weaken summer monsoon. The central Bay of Bengal experienced little temperature change, but surface waters were more saline. The averaged usd\delta\spusdC of these three species from Recent coretops is well correlated to average (PO4) concentrations from 0 to 125 meters depth, and therefore is used to estimate near-surface usd\delta\spusdC-CO{2-seawater}. Estimates of LGM Indian Ocean usd\delta\spusdC-CO2, corrected for an estimated whole-ocean glacial-to-interglacial usd\delta\spusdC shift, shows most Indian Ocean surface waters were substantially enriched in C (+0.3usd\perthoususd to +0.6usd\perthous\ \delta\spusdC) during the LGM, with only the northwestern Arabian Sea recording somewhat lighter usd\delta\spusdC. Integrated with estimates of paleocirculation and paleotemperatures, our LGM surface water usd\delta\spusdC-CO2 reconstruction supports evidence for reduced Summer Monsoon strength and cooler sea surface temperatures in the southeastern Indian Ocean. Significant increases in nutrient supply or decreased productivity are inferred for the region northwest of Australia and the far western Indian Ocean.
Subject	:	Biogeochemistry
	:	Earth sciences
	:	Geochemistry
	:	Geology
	:	Globigerinoides
	:	Globorotalia