Graduation Year

2008

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Benjamin P. Flower, Ph.D.

Keywords

Tropics, Climate, Stable isotope, Salinity

Abstract

Sea surface temperature (SST) reconstructions from the low latitudes indicate the tropics/subtropics warmed significantly before glacial-interglacial decreases in global ice volume, suggesting the importance of tropical and subtropical climate in driving glacial terminations. ODP Site 625, drilled at a water depth of 889 m near De Soto Canyon in the Gulf of Mexico (GOM), provides continuous records of marine isotope stages (MIS) 1-6 sampled at a mean temporal resolution of 400 years. Age control is based on 8 AMS radiocarbon dates, marine isotope stratigraphy, and Foraminifera datum levels. Results from Globigerinoides ruber (white variety) Mg/Ca-SST indicate a rise of 4.4 °C from last glacial maximum to modern conditions and a 3.2 °C rise from the penultimate glaciation to the last interglaciation. However, model results suggest reduced thermohaline circulation (THC) causes salt and heat build-up in the Atlantic Warm Pool.

Paired G. ruber Mg/Ca-SST and d¹8O provide evidence of sub-millennial scale variability in GOM SST and SSS that is probably influenced by the strength of NADW production, as also observed in the Western Caribbean Sea. We test the idea that widespread abrupt climate change during the last glaciation caused by millennial scale fluctuations in the intensity of THC was modulated by Laurentide ice sheet (LIS) meltwater routed to the North Atlantic. To understand LIS melting dynamics and test the Meltwater Routing Hypothesis, we investigate the phasing of GOM SST and LIS freshwater events in relationship to high latitude climate. Estimated salinities from our multi-proxy approach suggest three freshwater events with a major freshwater influx from that occurred during Heinrich Event 2. This result confirms previous studies that suggested LIS summer melting during warmings in Antarctica. We also find a climate reversal during termination II from 130.4-128.4 ka.

The initial rise in GOM SST at 132.1 ka of 2.9 °C is followed by a cold reversal of 1.5 °C at 130.4 ka for 2 ky and final increase to full interglacial warmth. The reversal in GOM SST is consonant with a pause in sea level rise and reduced NADW, suggesting a reduction in THC may have caused a global two-step deglaciation.

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