HR: 0800h
AN: PP41B-0644    [Abstracts]
TI: The Bermuda Rise Record of MIS 11-12: Inferences from Organic Carbon Fluxes, Organic Matter Isotopic Composition and Benthic Foraminifera
AU: * Poli, M
EM: mpoli@emich.edu
AF: Eastern Michigan University, Department of Geography and Geology, Ypsilanti, MI 48197
AU: Meyers, P A
EM: pameyers@umic.edu
AF: The University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1005
AU: Thunell, R C
EM: thunell@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences, Columbia, SC 29208
AU: Capodivacca, M
EM: mcapodiva@emich.edu
AF: Eastern Michigan University, Department of Geography and Geology, Ypsilanti, MI 48197
AB: We examined organic carbon content, organic matter carbon and nitrogen isotopic composition and benthic foraminiferal assemblages in sediments deposited between 500-390 ka on the northeastern flank of the Bermuda Rise (ODP Site 1063, 4584m water depth). This time interval includes Marine Isotope Stage 11 (MIS 11, ca 423 to 362 ka), a particularly warm and long interglacial characterized by a configuration of the Earth's orbit similar to today, and MIS 12, one of the most severe glacials of the last 600 ky. Sedimentation rates at Site 1063 are high due to advection of clay and silt into the region by deep recirculating gyres. In the study interval, we reconstructed values ranging between 7 cm/ky during MIS 11 and up to 50 cm/ky during MIS 10 and 12. Our organic carbon data show higher percentages and accumulation rates during MIS 10 and 12, in correspondence with the highest sedimentation rates (30-50 cm/ky). This pattern suggests a combination of enhanced organic matter production and preservation at these times. Del 13C and 15N values are lower during the MIS 10 and 12 than during MIS 11; a similar pattern is recorded at ODP Site 1058 (Blake Ridge) and may be the result of glacial-interglacial changes in the organic matter recycling in the western North Atlantic, possibly linked to sea level changes and consequent shifts in the area where nutrient recycling occurs. Benthic foraminiferal assemblages are dominated by N. umbonifer during MIS 11, a species adapted to oligotrophic environments, and by O. umbonatus during glacial intervals, a taxon that is more common below zones of seasonally high surface production in water deeper than 2km, and probably prefers low but sustained flux of highly degraded organic material. The beginnings of the MIS 10 and MIS 12 glaciations are characterized by large, rapid increases in the abundance of E. exigua, a species that inhabits seasonally deposited aggregates of phytodetritus produced during spring plankton blooms, thus suggesting an increase in surface ocean primary productivity at these times.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4944 Micropaleontology (0459, 3030)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005