HR: 11:20h
AN: PP52A-05    [Abstracts]
TI: A Record of the Eastern Tropical Pacific of Water Column Structure Reorganization during the Rapid Climate Changes of Marine Isotope Stage 3.
AU: * Hendy, I L
EM: ihendy@umich.edu
AF: University of Michigan, 1100 North University Ave, Ann Arbor, MI 48109-1005, United States
AB: Little is known about the details of paleoceanographic changes in the Eastern Tropical Pacific (ETP) during marine isotope stage 3. Here we present a high resolution record of climate change from core ME0005A 10JC (15.7°N; 95.3°E, 1040 m water depth) collected in the Gulf of Tehuantepec spanning 48 to 38 Ka. Planktonic and benthic stable isotope records have been generated alongside Corg, carbonate, δ15N and trace metal concentrations of bulk sediments. Seasonal intense wind forced upwelling produces high Corg flux in the Gulf. In winter, high atmospheric pressures in the Gulf of Mexico and low pressures in the ETP (associated with the ITCZ) create a strong pressure gradient generally blocked by high mountains along the isthmus. A gap near the Gulf of Tehuantepec allows air to spill over into the Pacific creating a hurricane force wind (the Tehuanos) that pushes water off the broad shelf, producing non-Ekman upwelling. Corg production increases from 48 to 38 Ka in association with increasing nitrate utilization as indicated by increasing δ¹⁵N values. Conservative trace metals increase relative to non-conservative between 45 and 43 Ka simultaneously with shift to more positive benthic δ¹³C, while non-conservative (nutrient- like) metals increase after 43 Ka. A prominent short ~1‰ negative shift in benthic δ¹⁸O occurs at 44.5 Ka with a 0.5‰ positive step occurring at 43.5 Ka. Globigerina ruber records δ¹⁸O values of ~-1‰ between 46 and 45 Ka, decreasing by ~1‰ at 45 Ka, while δ¹³C values vary between 0 and 1‰. Globigerina bulloides records δ¹⁸O values of ~0.5‰ and δ¹³C of 1‰ between 46 and 45 Ka, but records δ¹⁸O values of ~-1‰ and δ¹³C of -1‰ between 44 and 42 Ka. G. bulloides is associated with winter upwelling in the region, while G. ruber is a surface dweller associated with the Costa Rica Current that enters the Gulf in summer. Neogloboquadrina dutertrei and Globorotalia menardii generally record δ¹⁸O values of 0.5 to 0‰ and δ¹³C of 1‰, however, between 46.3 and 45.5 Ka these deep dwellers record δ¹⁸O values similar to G. ruber and δ¹³C values of -2‰. N. dutertrei and G. menardii are both deep dwelling foraminifera also associated with the Costa Rica Current. Clearly between 46 and 45 Ka, major changes occur in the surface waters that do not affect waters at 1000m water depth. The upper water column becomes isothermal between 46.3 and 45.5 Ka, yet a strong nutricline exists. Seasonal SST differences increase, while upwelling was apparently reduced. The timing of these changes between Interstadial 15 and 14 is suggestive of Heinrich 6 influencing atmospheric circulation in the ETP however, ~5 Ka calibration errors exist that make such a correlation difficult.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4926 Glacial
DE: 4954 Sea surface temperature
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly