HR: 0800h
AN: PP11A-0201    [Abstracts]
TI: Circulation Through the Central American Seaway During the Miocene Carbonate Crash
AU: * Newkirk, D R
EM: drnewk@ufl.edu
AF: Department of Geological, University of Florida, Gainesville, FL 32f611, United States
AU: Martin, E E
EM: emartin@geology.ufl.edu
AF: Department of Geological, University of Florida, Gainesville, FL 32f611, United States
AB: Changes in deep sea circulation in the Caribbean Basin were investigated in order to determine the cause of the carbonate crash in the middle to late Miocene and the impact of the shoaling of the Central American Seaway (CAS) on larger scale circulation patterns. Gateway events, such as the shoaling of the CAS, have long been associated with the reorganization of ocean circulation and dramatic climate events. The distribution of water masses in the Caribbean region was evaluated using Nd isotopes from fossil fish teeth from three ODP sites: Site 998 in the northern Caribbean Basin (3179 m water depth), Site 999 in the southern Caribbean (2897 m), and Site 846 from the eastern equatorial Pacific (3296 m). Prior to the carbonate crash in the Caribbean (14 to 12 Ma) ε_Nd values increased from -6 to ~-3, while carbonate mass accumulation rates \(MARs\) decreased. During the crash interval ε_Nd values were highly variable within the Caribbean basin with values ranging between -4.4 and 0; the highest values correlate with intervals of greatest dissolution. As carbonate MARs increased following the crash ε_Nd values in the Caribbean began to decrease, reaching a value of ~-6 by 9 Ma. The carbonate crash in the eastern equatorial Pacific lags the Caribbean crash by about 0.5 Ma. Prior to the crash ε_Nd values at Site 846 increased from -4 to -2. They then remained relatively steady during the crash. The radiogenic Nd values in the Caribbean basin are much higher than any values recorded in the Atlantic throughout the Cenozoic. The possibility that these values are altered by ash diagenesis in the Caribbean has been evaluated, but there is no correlation between intervals of ash deposition and radiogenic ε_Nd values. However, these radiogenic values are similar to values reported for Pacific intermediate and shallow waters during the Miocene. It appears that corrosive, intermediate Pacific waters were gradually introduced into the Caribbean prior to the crash, while pulses of almost exclusively shallow to intermediate Pacific waters filled the Caribbean during the crash. This inflow of Pacific waters through the CAS has been predicted by several GCMs investigating the affects of CAS sill depths and the location of the ITCZ on Northern Component Water (NCW) production and flow directions through the CAS. Periods of enhanced NCW production correlate with intervals of more intense dissolution in the Caribbean, suggesting that aging of the water along the conveyor belt flow path from the North Atlantic to the Pacific creates more corrosive Pacific Deep Water, which then contributes to North Pacific Intermediate Water and Pacific Central Water. These corrosive waters flow southward producing more radiogenic ε_Nd values and carbonate dissolution in the equatorial Pacific and Caribbean Basin. Shoaling of the CAS and a decrease in NCW combine to limit the flow of radiogenic, corrosive waters into the Caribbean. This reduction in Pacific throughflow is documented by the decreasing ε_Nd values beginning at ~10 Ma at Site 998 and continues until ~5Ma as documented by ε_Nd data from a ferromanganese crust located in the Straits of Florida.
DE: 1040 Radiogenic isotope geochemistry
DE: 4532 General circulation (1218, 1222)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting