HR: 08:15h
AN: PP41F-02    [Abstracts]
TI: A New Stable Isotope Record From the Subantarctic Southeastern Pacific
AU: * Waddell, L M
EM: waddelin@umich.edu
AF: Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, United States
AU: Hendy, I L
EM: ihendy@umich.edu
AF: Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, United States
AU: Moore, T C
EM: tedmoore@umich.edu
AF: Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, United States
AU: Lyle, M W
EM: mlyle@cgiss.boisestate.edu
AF: Center for Geophysical Investigation of the Shallow Subsurface, Boise State University, Boise, ID 83725-1536, United States
AB: Few stable isotope records exist from the southeast Pacific Ocean due to its remote location, low sedimentation rates, and shallow carbonate compensation depth (CCD). The CCD in the southeast Pacific, however, has been found to be unusually deep (~4750 m), thereby allowing for the preservation of Neogene carbonates at abyssal depths. Herein we present stable isotope results from MV0502-4JC, which was recently recovered from the subantarctic region of the Southwest Pacific (50°20S, 148°08W, 4286 m). Dating the record with radiolarian biostratigraphy, we have generated a benthic stable isotope record back to the Middle Miocene from Cibicidoides spp. and a planktic record from Globigerina bulloides into the Late Pliocene. These stable isotope records, in conjunction with carbonate contents and counts of ice-rafted debris (IRD) and manganese micronodules show the effect of global ice sheet build up on this poorly understood region. A prominent negative δ¹³C shift of ~1‰ (from ~1 to ~0.2‰) in the benthic record occurs at ~15.3 MBSF (Middle Miocene) as carbonate contents in the core decrease from ~80% to ~20%, and significant changes in the bottom water are indicated by changes in the dominant Cibicidoides spp. at the site from C. robertsonianus to C. wuellerstorfi. Trace amounts of IRD and abundant manganese micronodules also appear at the site at this time. A significant hiatus (from the Late Miocene to the Middle Pliocene) occurs somewhere between 11.4 and 9.8 MBSF. From 9.8 to 8 MBSF (Late Pliocene) benthic δ¹⁸O increases and δ¹³C decreases by ~1‰. Also, IRD increases, manganese micronodules decrease, and there is a dramatic increase in the preservation of planktic foraminifera at the site. A planktic δ¹³C shift of >1‰ (from 0 to 1‰) occurs at ~5 MBSF (Pleistocene) coincident with a 20% increase in carbonate concentration. After this interval, the variability in both benthic δ¹⁸O and δ¹³C and planktic δ¹⁸O increases significantly. We interpret the negative δ¹³C shift at 15.3 MBSF as the end of the Monterey Carbon Excursion (~13.5 Ma), and the decrease in carbonate observed in MV0502-4JC following this shift may correspond with a widespread hiatus (NH3) associated with the increased presence Antarctic Bottom Water (AABW) in the Pacific and shoaling of the lysocline. The significant hiatus in the Late Miocene-Early Pliocene may also indicate increased AABW formation and Antarctic Circumpolar Current strength during key periods of ice sheet expansion on Antarctica. The ~1‰ increase in benthic δ¹⁸O in the Late Pliocene is interpreted as the onset of Northern Hemisphere Glaciation, although the planktic δ¹⁸O record oddly does not show this trend. Increased lysocline depth during the Late Pliocene preceded the high (~30 cm kyr^-1) sedimentation rates of the Early Pleistocene that may have resulted from reduced bottom water currents and/or increased productivity. The Late Pleistocene was associated with lower sedimentation rates perhaps associated with increased non-carbonate productivity and increased AABW production during glacial intervals.
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 9355 Pacific Ocean
DE: 9605 Neogene
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting