HR: 1340h
AN: PP23B-1414    [Abstracts]
TI: Decadal-Scale Variations in Eastern Pacific Thermocline Structure from Soledad Basin, Baja California
AU: Levi, C
EM: clevi@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: * van Geen, A
EM: avangeen@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: Ortiz, J D
EM: jortiz@kent.edu
AF: Department of Geology, Kent State University, Kent, OH 44242 United States
AU: Zheng, Y
EM: yzheng@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: Marchitto, T M
EM: tom.marchitto@colorado.edu
AF: Department of Geological Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Dean, W E
EM: dean@usgs.gov
AF: Earth Surface Processes, US Geological Survey, Denver, CO 80225 United States
AU: Carriquiry, J
EM: jose_carriquiry@uabc.mx
AF: Instituto de Investigaciones Oceanologicas, Universidad Autonoma de Baja California, Ensenada, BC 22830 Mexico
AB: Soledad Basin, a semi-enclosed basin on the Pacific margin of southern Baja California at 25oN, is ideally located to document past variations of ocean/atmosphere interactions responding to the Pacific Decadal Oscillation (PDO) and the El Nino-Southern Oscillation (ENSO). Very high sedimentation rates (~108 cm/kyr; van Geen et al., Paleoceanography, v. 8, no. 4, 2003) combined with low bottow-water oxygen levels have prevented sediment bioturbation throughout the Holocene, setting the stage for high-resolution paleoclimatic reconstructions in this key climatic area. Current studies of this site focus on the combination of a 210Pb-dated multicore and 14C-dated gravity and piston cores. Available data include a 1-cm resolution diffuse spectral reflectance record, indicative of diagenetic processes linked to productivity (Ortiz et al., Geology, v. 32, no. 6, 2004) and Mg/Ca ratios for several planktonic foraminifera species. Mg/Ca results for two shallow-dwelling species in the multicore indicate little change in sea surface temperature (+/-1.1 deg C) over the mean value of 23 deg C observed over the past two centuries. In contrast, variations of Mg/Ca ratios for a deeper-dwelling species suggest considerably larger temperature variations of +/-1.8 deg C with respect to the mean value of 17.5 deg C at the depth habitat of this species. This suggests fluctuations in the temperature, and therefore nutrient content, of thermocline waters upwelling toward the surface at this site without any appreciable changes in upwelling. Periods of low subsurface temperatures in the water column inferred from Mg/Ca correspond to darker sediment bands, suggesting a connection between the structure of the thermocline, the supply of nutrients to the photic zone, and surface productivity. This interpretation is supported by elevated authigenic Mo concentrations in those same dark bands of 30-40 mg/kg. The presentation will include a comparison of these results with instrumental and other proxy climate records of the region and an extension of detailed reconstructions to several intervals of the Holocene.
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting