HR: 0800h
AN: PP51F-1370    [Abstracts]
TI: Metal Deposition Along the Peru Margin Since the Last Glacial Maximum: Evidence For Regime Change at \sim 6ka
AU: * Tierney, J
AF: Brown University, Dept. of Geological Sciences, Providence, RI 02912-1846 United States
AU: Cleaveland, L
EM: Laura_Cleaveland@brown.edu
AF: Brown University, Dept. of Geological Sciences, Providence, RI 02912-1846 United States
AU: Herbert, T
EM: Timothy_Herbert@brown.edu
AF: Brown University, Dept. of Geological Sciences, Providence, RI 02912-1846 United States
AU: Altabet, M
EM: maltabet@umassd.edu
AF: Univ. Mass. Dartmouth, CMAST 706 Rodney French Blvd., New Bedford, MA 02744-1221 United States
AB: The Peru Margin upwelling zone plays a key role in regulating marine biogeochemical cycles, particularly the fate of nitrate. High biological productivity and low oxygen waters fed into the oxygen minimum zone result in intense denitrification in the modern system, the consequences of which are global in nature. It has been very difficult, however, to study the paleoclimatic history of this region because of the poor preservation of carbonate in Peru Margin sediments. Here we present records of trace metal accumulation from two cores located in the heart of the suboxic zone off the central Peru coast. Chronology comes from multiple AMS $^{14}$C dates on the alkenone fraction of the sediment, as well as correlation using major features of the \delta $^{15}$N record in each core. ODP Site 1228 provides a high resolution, continuous sediment record from the Recent to about 14ka, while gravity core W7706-41k extends the record to the Last Glacial Maximum. Both cores were sampled at a 100 yr resolution, then analyzed for % N, \delta $^{15}$N, alkenones, and trace metal concentration. Analysis of redox-sensitive metals (Mo and V) alongside metals associated with changes in productivity (Ni and Zn) provides perspective on the evolution of the upwelling system and distinguishes the two major factors controlling the intensity of the oxygen minimum zone. The trace metal record exhibits a notable increase in the intensity and variability of low oxygen waters and productivity beginning around 6ka and extending to the present. Within this most recent 6ka interval, the data suggest fluctuations in oxygenation and productivity occur on 1000 yr timescales. Our core records, therefore, suggest that the Peru Margin upwelling system strengthened significantly during the mid to late Holocene.
DE: 4267 Paleoceanography
DE: 4802 Anoxic environments
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1620 Climate dynamics (3309)
DE: 0330 Geochemical cycles
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting