HR: 10:20h
AN: PP32A-01    [Abstracts]
TI: Mg/Ca in extra-tropical planktonic foraminifera: trap, tow and culture results from Santa Barbara Basin
AU: * Pak, D K
EM: pak@geol.ucsb.edu
AF: U C Santa Barbara, Dept. of Earth Science and Marine Science Institute, Santa Barbara, CA 93106 United States
AU: von Langen, P
EM: Pvonlangen@waterboards.ca.gov
AF: Central Coast Regional Water Board, 895 Aerovista Place, Suite 101, San Luis Obispo, CA 93401 United States
AU: Lea, D W
EM: lea@geol.ucsb.edu
AF: U C Santa Barbara, Dept. of Earth Science and Marine Science Institute, Santa Barbara, CA 93106 United States
AU: Kennett, J P
EM: kennett@geol.ucsb.edu
AF: U C Santa Barbara, Dept. of Earth Science and Marine Science Institute, Santa Barbara, CA 93106 United States
AB: Although Mg/Ca in planktonic foraminifera is now widely used as a sea surface temperature proxy, most published studies have focused on tropical species. The temperate and subpolar species Globigerina bulloides and Neogloboquadrina pachyderma however, are equally important for reconstructing near-surface and sub-surface temperatures in extratropical regions. Sediment trap time series, plankton tows and culturing experiments provide an opportunity to compare foraminiferal Mg/Ca with in-situ water temperatures and to calibrate foraminiferal Mg/Ca from the sediment record. We present Globigerina bulloides and Neogloboquadrina pachyderma (d.) Mg/Ca records from a sediment trap deployed in Santa Barbara Basin between 1995 and 1999. Results of bi-weekly samples indicate that the Mg/Ca values of these species reflect measured seasonal variations in temperature of the near-surface (20-30 m) and sub-thermocline depths (75-100 m), respectively, and are additionally well-correlated with oxygen isotopic temperatures from the same samples. The average deviation between Mg-based temperatures and δ¹⁸O -based temperatures is 0.6°C for G. bulloides and 0.8°C for N. pachyderma (d.). Similarly, foraminiferal Mg/Ca from Santa Barbara Channel plankton tows support a below thermocline calcification depth for N. pachyderma (d.). The sediment trap and tow results lend strong support for the accuracy of culture-based Mg-temperature calibration equations for G. bulloides and N. pachyderma (d.), and suggest that calibration equations for these species are determined by a higher pre-exponential constant than those based on tropical species. Thus, reconstruction of past temperatures using Mg/Ca requires calibration equations appropriate for different latitudes.
DE: 4279 Upwelling and convergences (4964)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4924 Geochemical tracers
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005