HR: 0800h
AN: PP41D-0787    [Abstracts]
TI: A middle Miocene onset of a permanent sea-ice cover in the Arctic Ocean
AU: Krylov, A
EM: akrylow@gmail.com
AF: Vniiokeanologia, Angliysky pr. 1, St. Petersburg, RU-190121, Russian Federation
AU: * Backman, J
EM: backman@geo.su.se
AF: Stockholm University, Dept. Geology & Geochemistry, Stockholm, SE-10691, Sweden
AU: Andreeva, I A
EM: andreevairi@yandex.ru
AF: Vniiokeanologia, Angliysky pr. 1, St. Petersburg, RU-190121, Russian Federation
AU: Vogt, C
EM: cvogt@uni-bremen.de
AF: University of Bremen, Dept. of Geosciences, Bremen, DE-28359, Germany
AU: Krupskaya, V V
EM: vi_kru@bk.ru
AF: Russian Academy of Science, Inst. Geology of Ore Deposits, Petrography, Mineralogy & Geochemistry, Moscow, RU-119017, Russian Federation
AU: Grikurov, G E
EM: grikurov@mail.ru
AF: Vniiokeanologia, Angliysky pr. 1, St. Petersburg, RU-190121, Russian Federation
AU: Moran, K
EM: kate.moran@gso.uri.edu
AF: University of Rhode Island, Graduate School of Oceanography & Dept. of Ocean Engineering, Narragansett, RI 02882-1197,
AB: The Arctic Coring Expedition (ACEX) penetrated over 400 m of Cenozoic sediments from the central part of the Lomonosov Ridge in the Arctic Ocean. The pervasive occurrence of dropstones and sand lenses in the Neogene ACEX sediments, which clearly are of terrigeneous origin, must have been brought to this mid-oceanic location by sea-ice and icebergs. Critical to understanding the paleoclimate history of the Arctic is a reconstruction of the magnitude and timing of the occurrence of perennial sea-ice. Unambiguously determining whether or not the sea-ice was seasonal or perennial is a challenging undertaking. One approach to addressing this challenge is to determine the source areas of the mineral assemblages that were deposited at the ACEX drill site. To establish the source areas for the terrigeneous material, the mineralogical composition of the upper 300 m of drilled sequence was investigated. Heavy and clay mineral associations indicate a major and consistent shift in provenance that occurs across a boundary at ca. 156 meters below seafloor. This boundary defines a change in source region from the Barents-Kara-western Laptev Sea, identified by the presence of common clinopyroxene and smectite below 156 m, to the eastern Laptev–East Siberian seas above 156 m, identified by common hornblende (amphibole) and illite. Bccause of the geographic distance, sea-ice originating from the eastern Laptev–East Siberian seas source region would have survived at least one summer melt cycle in order to reach the ACEX drill site, based on modern sea-ice trajectories and velocities. This shift in mineral assemblages, and thus source areas, is interpreted to represent the onset of a perennial sea-ice cover in the Arctic Ocean, which occurred at about 13 Ma, indicating a coeval cooling in the Arctic and Antarctic regions.
DE: 3022 Marine sediments: processes and transport
DE: 3036 Ocean drilling
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting