HR: 0800h
AN: PP31A-0887    [Abstracts]
TI: Planktonic Foraminifera Study at Site ODP 999A (Caribbean Sea): Insights into Oceanic Exchange and Paleocirculation During the last 450 Kyrs.
AU: Vautravers, M J
EM: mv217@cus.cam.ac.uk
AF: The Godwin Laboratory, Earth Sciences dept, University of Cambridge, New Museum SitePembroke Street, Cambridge, CB3 2SA United Kingdom
AU: * Spero, H J
EM: spero@geology.ucdavis.edu
AF: Geology dept, University of California, One Shields Ave., Davis, CA 95616 United States
AU: Schmidt, M W
EM: schmidt@geology.ucdavis.edu
AF: Geology dept, University of California, One Shields Ave., Davis, CA 95616 United States
AB: A recent micro-palaeontological study of a core from the South Atlantic (Peeters et al., Nature. 430, 661, 2004) stresses the importance of the Agulhas leakage intensity as a key control on North Atlantic Thermohaline operation. Planktonic foraminifera counts were conducted on the Colombian Basin core ODP 999A ($12\deg$N, $74\deg$W, 2878 m); results are presented on a SPECMAP-based age model (Schmidt et al., in prep 2004). At present both climate and surface circulation are driven by the motion of the Intertropical Convergence Zone (ITCZ), which governs dry/wet seasons and upwelling intensity. Caribbean surface water originates from both the south Atlantic, which re-circulates Indian Ocean water, and the north Atlantic subtropical gyre. Similarly the deep-water is a mixture of AAIW and UNADW, originating in the southern and northern hemispheres respectively. A CaCO$_{3}$ preservation index, which is deduced from planktonic fragments and pteropod remains, is used to trace changes in the intermediate water mixture. This study confirms that the sediments are better preserved during glacial times. Furthermore, it shows that the sediments of MIS11 are intensely dissolved, suggesting a maximal contribution of AAIW. Over the last 450 kyr, we observe a decreasing contribution of the AAIW during both interglacial and glacial times. In addition, the Holocene appears unusual, with a low AAIW to UNADW ratio in comparison to previous warm intervals. An examination of the percentages of the surface Indo-Pacific species {\it G. menardii} seems to confirm part this result, identifying MIS11 as a time of maximal Indian-Atlantic exchange via the Agulhas 3valveŭ. It also confirms that during MIS2, 3 and 4, Caribbean surface waters were unusually unfavourable for this species and/or that the Agulhas connection was absent. The % of {\it G. Hexagona}, another Indo-Pacific species, which lives in deeper thermocline waters, peaks during MIS11, MIS9e, MIS7c and MIS5e but is absent during the Holocene and MIS7e. This observation suggests a slightly different scenario for the intermediate water flowing through the 3valveŭ. This confirms the peculiarity of the Holocene as was found on the basis of benthic \delta$^{13}$C measurements in the North Atlantic (Raymo et al., Paleoceanography. 19, PA2008, 2004). Finally, on the basis of the species mentioned above in the Caribbean Sea we cannot find evidence of enhanced exchange between the Indian and the Atlantic at the end of the past five glacial as found in the Agulhas area. This disagreement and the factors controlling the late reappearance of these species in the Caribbean Sea need further investigation.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting