HR: 17:15h
AN: PP34B-06    [Abstracts]
TI: Biennial Record of Northeast Pacific Ventilation Over the Past two Centuries: Radiocarbon and Benthic Foraminferal Evidence From the Santa Barbara Basin
AU: * Roach, L D
EM: lroach@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr Mail Code, La Jolla, CA 92093, United States
AU: Field, D B
EM: dfield@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Guilderson, T P
EM: tguilderson@llnl.gov
AF: Center for Accelerator Mass Spectrometry, Lawrence Livermore Natl. Laboratory, P.O. Box 808 L-397, Livermore, CA 94550, United States
AU: Charles, C D
EM: ccharles@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr Mail Code, La Jolla, CA 92093, United States
AB: By volume considerations alone, the ventilation of the interior North Pacific Ocean must play a crucial role in global climate dynamics on timescales of decades to centuries. However, the sub-thermocline dynamics of the North Pacific remain largely inaccessible beyond sparse instrumental observations spanning the last twenty years. The annually laminated sediments of the Santa Barbara Basin (SBB) provide a unique opportunity to document subsurface variability over the last few centuries. The radiocarbon age of benthic foraminifera from a box core removed at the basin bottom (578 m) was measured at biennial resolution through 1819 to create a continuous benthic Δ¹⁴C record. In addition to Δ¹⁴C analysis, benthic foraminiferal species assemblages were quantified at the same resolution through 1736. Comparison of radiocarbon results with instrumental measurements reveals that benthic foraminfera faithfully capture the Δ¹⁴C of bottom water dissolved inorganic carbon (DIC). We observe substantial Δ¹⁴C variability on interannual to decadal timescales with excursions of as much as 40‰. Significant correlations of the radiocarbon record with SST records and PDO reconstructions suggest for the influence of decadal scale North Pacific climate on the vertical density structure of the northeast Pacific margin as the driver of Δ¹⁴C variability, although pore-water chemistry and advection of intermediate water masses may also contribute. The cosmopolitan benthic foraminifera of the SBB exhibit a pattern of decadal variability similar to that observed in the Δ¹⁴C time series with the exception of one chloroplast bearing species, ( Nonionella stella), which experiences unprecedented growth over the late 20^th century. While the mechanism driving this growth and behavioral deviation from the other species remains unclear, the sensitivity of benthic foraminifera to their environment hints at subtle chemical and/or physical changes in the SBB benthos occurring over the last three decades. These records provide a means for discriminating the mechanisms of natural sub-surface variability in the North Pacific and to resolve the interaction between bottom water chemistry and benthic ecosystems.
DE: 4513 Decadal ocean variability (1616, 1635, 3305, 4215)
DE: 4802 Anoxic environments (0404, 1803, 4834, 4902)
DE: 4806 Carbon cycling (0428)
DE: 4860 Radioactivity and radioisotopes
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting