HR: 1340h
AN: PP43C-1534 [Abstracts]
TI: A Late Miocene-Pliocene Antarctic Deepwater Record of Cyclic Iron Reduction Events (ODP Leg 178 Site 1095)
AU: Hepp, D A
EM: dhepp@uni-bremen.de
AF: Department of Geosciences, Bremen University, P.O.Box 330440, Bremen, 28334,
Germany
AU: * Moerz, T
EM: tmoerz@uni-bremen.de
AF: Department of Geosciences, Bremen University, P.O.Box 330440, Bremen, 28334,
Germany
AU: * Moerz, T
EM: tmoerz@uni-bremen.de
AF: DFG Research Center Ocean Margins, Bremen University, P.O.Box 330440, Bremen,
28334, Germany
AB:
The Pacific margin off the Antarctic Peninsula is very sensitive to climate and ice-sheet volume changes. Climatic
variations on the continental shelf control regional sedimentary processes and foster the build-up of giant deep-
sea sediment drifts. These drifts represent the most proximal continuous sedimentary recorders for West
Antarctic ice sheet evolution and glacial-interglacial cyclicity pattern. Sediment physical, geochemical records and
x-ray images derived from ODP Site 1095 (Drift 7) were used to identify pattern in glacial-interglacial cyclicity and
associated sedimentary and diagenetic processes during late Miocene and Pliocene. Two boundary types
dividing half-cycles have been recognized: (1) interglacial-to-glacial transitions are characterized by a sharp
boundary and abrupt change in lithology; (2) glacial-to-interglacial transitions can described as a gradual change
from a full glacial to a full interglacial stage. A prominent feature of the glacial-to-interglacial transition is the loss
of the magnetic susceptibility signal, caused by diagenetic alteration and demagnetization of magnetic iron
minerals in a suboxic to anoxic sediment environment. Similar redox processes are described for organic carbon
rich Madeira abyssal plain turbidites and Mediterranean sapropels, but are uncommon for vented Circum-
Antarctic deep-sea sediments. Iron reduction zones were coupled to the ice sheet collapse at the end of
deglaciation phases. Ice sheet collapse and meltwater formation weaken the bottom water formation and
convection, but foster short living diatom blooms resulting in high fluxes of organic matter to the seafloor. Iron
reduction zones were observed in sixty-four zones of ODP Site 1095 cores. Thus, the sedimentary record of Drift 7
affords an unique opportunity to study cyclic iron reduction events at long time-scales. The occurrence and
intensity of those 'diagenetic zones' reflect long-term trends of global climate change and the related variability of
primary production and preservation of organic matter. The study describes the complex interaction of Antarctic
ice sheet behavior and ocean conditions in warmer late Miocene to Pliocene climate and may serve as an outlook
for upcoming changes in the Circum-Antarctic realm in the course of recent global warming.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0726 Ice sheets
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting