HR: 0800h
AN: PP11A-0544    [Abstracts]
TI: Oceanographic Influences in the Variability Of $\delta$$^{13}$C and $\delta$$^{18}$O in Benthic and Planktonic Foraminiferal From the Gulf of California
AU: * Staines-Urias, F
EM: staines@usc.edu
AF: University of Southern California, 3651 trousdale Parkway, SCI 117, Los Angeles, CA 90089-0740 United States
AU: Douglas, R G
EM: rdouglas@usc.edu
AF: University of Southern California, 3651 trousdale Parkway, SCI 117, Los Angeles, CA 90089-0740 United States
AB: The analysis of multicore samples collected during CALMEX-NH01 cruise (2001) in two locations of the Gulf of California provide information regarding changes in climate and oceanography of the region. Alfonso Basin on the western side and Pescadero Basin on the center slope of the east side of the Gulf, are marginal basins with sills or shoreward slopes in the Oxygen Minimum Zone. Each basin represents different oceanographic conditions in the Gulf, which can be recognized in the sedimentary history. In Pescadero Basin, accumulation rates of 0.5 to 1.1mm/yr were calculated by $^{210}$Pb dating. For Alfonso basin accumulation rates between 0.24 and 0.32mm/yr were obtained by AMS radiocarbon analysis in foraminifera. The multicores were sampled at 2.2mm intervals (~3-5yr/sample in Pescadero, 6-8yr/sample in Alfonso) to produce a high-resolution record of $\delta$$^{18}$O and $\delta$$^{13}$C based on benthic ({\it Bolivina subadvena}) and planktonic ({\it Globigerina bullloides}) foraminifera. For the past 100 years, a visual comparison between {\it G. bulloides} $\delta$$^{18}$O calculated sea surface temperature (SST) time series from Pescadero Basin and a 5-years moving average of the annual Pacific Decadal Oscillation (PDO), revealed a good agreement between both variables. The same comparison but using {\it G. Bulloides} $\delta$$^{18}$O calculated SST from Alfonso Basin, shown no similarities between SST and PDO time series. Such an important contrast between both records evidences a major influence of the Pacific Ocean on the east side of the Gulf due to the entrance of water from the California Current (CC), and a more direct influence of meteorological processes in the west side mainly due to the presence of Gulf of California Water (GCW) from the Northern Gulf. Isotopic ratios of benthic foraminifera for both basins also evidence oceanographic differences. For the last 40 years, the calculated average {\it B. subadvena} $\delta$$^{13}$C in Alfonso Basin is -0.832%o when Pescadero exhibits an average $\delta$$^{13}$C {\it B. subadvena} for the same period of -1.608%o, indicating differences in surface productivity rates for both sides and also a different quality of the organic matter reaching the bottom. However, downcore $\delta$$^{18}$O variations show that changes in SST associated with ENSO events leave a measurable signal in the composition of planktonic foraminifera in both basins, indicating that both basins are sensitive to major climatic changes. For the last 50yr, {\it G. bulloides} $\delta$$^{18}$O records from Alfonso and Pescadero Basins show negative excursions that can be associated with the 1972-73, 1982-83, 1986-88, and 1997-98 ENSO events.
DE: 3344 Paleoclimatology
DE: 4215 Climate and interannual variability (3309)
DE: 4243 Marginal and semienclosed seas
DE: 4267 Paleoceanography
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting