HR: 1340h
AN: PP13B-1287    [Abstracts]
TI: Sedimentary Redox Conditions, Biogenic Production, and Oxygenation of Southeast Pacific Intermediate Waters Over the Past 30 ky.
AU: * Muratli, J
EM: jmuratli@gmail.com
AF: College of Oceanic and Atmospheric Sciences Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331-5503, United States
AU: Mix, A
EM: amix@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331-5503, United States
AU: Chase, Z
EM: zanna@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331-5503, United States
AU: McManus, J
EM: mcmanus@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331-5503, United States
AB: We present data from SE Pacific sediments in an effort to characterize the paleo-redox conditions of shallow (~400-1000 m) subsurface sediments, and the water masses that overlie them, over the past 30 ky. The sediments were recovered during ODP Leg 202, and come from three sites: 1233, 1234, and 1235; together these three sites constitute a vertical transect of Antarctic Intermediate Water (AAIW). Site 1233, at 41°S, sits in the core of AAIW at 838 m depth. Site 1234, at 36°S, is located between AAIW and the Pacific Central Water (PCW) mass. Site 1235 (489 m) is located close to Site 1234, but is between AAIW and the overlying low- dissolved-oxygen Gunther Undercurrent (GUC) water mass. Recent sediments for sites 1234 and 1235 contain a rich signature of biogenic opal production and enrichments of iron and the authigenic metals U, Mo, and Re. At site 1234 there is a minimum in biogenic Si at approximately 20 ky followed by a slight increase and a second minimum between 12 and 5 ky. At both sites 1233 and 1234 the trace metals exhibit more structure during the period of roughly 15 to 30 ky as compared to the most recent 15 ky. The trace metal data at site 1234 shows a sharp reducing signature at ~17 ky (higher Mo, lower U:Mo ratios), bracketed by periods of more oxygenated conditions (lower Mo, higher U:Mo) back to ~22 ky, and forward to ~12 ky. This combination of low biological production and more oxygenated bottom water may suggest a period of increased AAIW ventilation as far north as site 1234. Although it is difficult at this point to unequivocally separate the impact of ventilation from production using our current data base, it does appear that some of the observed changes in sedimentary character may be ventilation-driven rather than driven by local production.
DE: 1051 Sedimentary geochemistry
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting