HR: 0800h
AN: PP41B-0647    [Abstracts]
TI: Changes in Southeast Pacific Upper Ocean Water Mass Signatures During the Warm Pliocene
AU: * Steph, S
EM: ssteph@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Tiedemann, R
EM: rtiedemann@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Sturm, A
EM: asturm@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Groeneveld, J
EM: jgroeneveld@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AB: Here, we present Pliocene planktonic foraminiferal stable isotope and Mg/Ca records from east Pacific ODP-Sites 1241 and 1236. Site 1241 is positioned below the North Equatorial Countercurrent northeast of Galapagos at 6°N. Site 1236 is located at 21°S near the western edge of the northward-flowing Peru Chile Current (PCC) in an oligotrophic region of the subtropical gyre. Our records cover the time interval from 5.5-2.1 Ma. This time interval was probably characterized by a permanent El Nino-like climate state as suggested by modeling studies and recent paleoceanographic evidence. We measured stable isotopes and Mg/Ca of G. sacculifer, G.tumida, and G. crassaformis to examine latitudinal and vertical changes in upper ocean hydrography. The time interval from 3.5-2 Ma provides isotope gradients that are similar to modern δ¹⁸O (temperature and salinity) and δ¹³C (nutrient) gradients. Strong deviations from this modern-like state mark the time interval from 4.4-3.9 Ma. At Site 1236, this interval is characterized by cooling of the mixed layer and cooling and higher nutrient concentrations at the bottom of the photic zone, whereas water mass signatures further below remained relatively constant from 4.4-2.1 Ma. These findings are in line with a westward expansion of the relatively cool and nutrient-rich PCC between 4.4-3.9 Ma. The observed changes may support the hypothesis of a Pliocene permanent El Nino-like state, as the southward expansion of warm water along the South American coast, the weakening of the south Pacific anticyclone and the northward movement of the Westerlies may have pushed the PCC closer to Site 1236. However, the change toward more modern-like conditions probably appeared during the mid-Pliocene.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005