Senior Theses 2006
Melissa Gilbert, December 2005. A high-resolution deglacial record of climate and melt water discharge in the Gulf of Mexico
Faculty Advisor: David Hastings
Sea surface temperature and d18Oseawater records from the Gulf of Mexico during the Younger Dryas will help distinguish different scenarios for abrupt climate change. This record represents the most detailed Mg/Ca sea surface temperature record of the BØlling-Allerod - Younger Dryas oscillation in the Gulf of Mexico. We sampled core MD02-2550 from Orca Basin to a resolution of ~20 yr. Mg/Ca ratios in Globigerinoides ruber (white) were analyzed to generate a sea surface temperature record using the calibration given in Dekens et al. (2002). A major sea surface temperature decrease of 3.0 °C is recorded in two steps: a 1 °C cooling at 13.4 ka, and a more rapid cooling of ~2.0°C in less than 100 years is observed starting at 13.0 ka. These cooler sea surface temperatures persist for 1000 yrs (12.9-11.9 ka), and likely correspond to the Younger Dryas stadial. A reciprocal warming is observed in three stages: a warming at of 2.5 °C over 300 years (12.7-12.4 ka), relatively constant temperatures for 500 years (12.4-11.9 ka), and a final warming of 2.0 °C over 200 years (11.9-11.7 ka). Paired with the Mg/Ca-derived sea surface temperature, d18Ocalcite data was generated to produce a d18Oseawater record. The abrupt change in d18O values correspond to an abrupt meltwater cessation or diversion from the Mississippi River at 13.5 ka B.P. Although there seems to be evidence of a meltwater diversion away from the Mississippi, the record does not support a shutdown of North Atlantic Deep Water formation. The dramatic cooling and meltwater lag lead us away from an ocean driven mechanism and toward an atmospheric cause for abrupt onset of the Younger Dryas stadial.