HR: 1340h
AN: OS33B-1265    [Abstracts]
TI: The View from Below: Benthic Foraminifera as Indicators of Deep Water Change in Cariaco Basin
AU: * Gibson, K A
EM: kgibson@rsmas.miami.edu
AF: University of Miami - Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Cswy, Miami, FL 33149, United States
AU: Peterson, L C
EM: lpeterson@rsmas.miami.edu
AF: University of Miami - Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Cswy, Miami, FL 33149, United States
AB: The Cariaco Basin off northern Venezuela is the largest anoxic basin in the world today after the Black Sea. High productivity from seasonal upwelling and circulation that is restricted by the relatively shallow (145 m) modern sill depth combine to produce the present state of anoxia below a depth of about 300 m, which in turn contributes to the preservation of finely laminated sediments on the basin floor. During the Last Glacial Maximum (LGM), and intermittently throughout the late Quaternary, anoxic conditions were interrupted and sediments show clear evidence of bioturbation and chemical signatures for the presence of oxygen. This implies a switch in the balance between oxygen supply and demand, the oceanographic and climatic controls for which are not fully understood. Benthic foraminifera preserved during intervals of deep basin oxygenation provide insights into the deep water conditions at those times. We report here benthic census data from the LGM section in ODP Site 1002. At first glance, oxygen in the deep waters during a time of lowered glacial sea level would seem counterintuitive since Cariaco Basin would have been largely isolated from the open Caribbean Sea and even more restricted in its circulation by inlet sills that shoaled to no more than 30 m depth. The paradigm that has emerged to date argues for reduced surface productivity and decreased oxygen consumption from organic remineralization as the key to the oxic conditions. However, benthic foraminifera suggest that increased salinity may play a role in driving basin ventilation at this time. Benthic foraminiferal diversity is greatest at the beginning and end of the LGM, with members of the genera Pyrgo, Quinqueloculina, and Triloculina conspicuously in low abundance. These miliolid genera, which are high-Mg calcite, dominate the middle of the LGM, together comprising as much as 95 percent of the benthic assemblage. Today, this sort of association is common in high salinity environments such as the Persian Gulf. Tritium measurements have implicated the input of warm, salty shelf waters as an important ventilation source for the modern basin. This mechanism may have helped maintain deep oxygen levels during the LGM when the basin was more restricted and the climate more arid than today.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4926 Glacial
DE: 4944 Micropaleontology (0459, 3030)
DE: 4950 Paleoecology
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting