HR: 11:05h
AN: PP32A-04    [Abstracts]
TI: The Passage of an oxygen-depleted water mass through the Pacific during Deglaciation.
AU: * Hendy, I L
EM: ihendy@umich.edu
AF: Department of Geological Sciences, University of Michigan 100 North University Ave, Ann Arbor, MI 48109 United States
AU: Pedersen, T F
EM: tfp@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria P.O. Box 3055 STN CSC, Victoria, BC V8W 3P6 Canada
AB: The discovery of millennial scale oscillations in the California Oxygen Minimum Zone (OMZ) in Santa Barbara Basin by Kennett and colleagues underscored the role of Intermediate Waters in climate change. Here we present the first record through deglaciation of OMZ strength between 540 and 750 meters water depth south of the modern influence of North Pacific Intermediate Water (NPIW). Redox chemistry from a core transect (15.7°N; 95.3°E; ME0005A-11PC and 3JC) in the Eastern Tropical Pacific (ETP) demonstrates that a poorly ventilated water mass bathed the slopes of the Gulf of Tehuantepec from ~{17 to 11 Ka. This is supported by a number of independent lines of evidence: The increase in trace metal concentration in bulk sediments, high δ¹⁵N values, and finally pronounced laminations in the core sediment fabric during this interval. Remarkably, peak values occur during the Bolling climatic event, similar to other Pacific Margin records.

During the Bolling an exceptionally strong productivity pulse occurs throughout the North Pacific within a number of different upwelling regimes including coastal and shelf break upwelling and open ocean spring blooms. Furthermore during this interval the OMZ on the California Margin strengthened beyond even that experienced during the Holocene. But rather than appealing to a synchronous `switching on' of upwelling throughout the North Pacific as an explanation for this, an alternate mechanism is the appearance of a high nutrient subsurface water mass circulating at intermediate water depths.

Although we cannot determine the source of this oxygen-poor water mass, its early arrival in the ETP is coincident with changes in Antarctic climate that resulted from the reorganization of intermediate water circulation in the South Pacific. Thus we link the ETP to Antarctic climatic change. The order of arrival of nutrient-rich water in each location tracks the path of intermediate water circulation in the North Pacific. ETP Intermediate Water contains components of Antarctic Intermediate Water, Subantarctic Mode Water and NPIW. It is advected throughout the North Pacific along two routes, in the west southward under the Kuroshio Current, and in the east, northward in the California Undercurrent. Oxygen isotope evidence supports the shutdown of Undercurrent flow during cool intervals so that oxygen depleted water that arrived in the ETP at 17 Ka could not be advected to the California region until the Bolling.
DE: 4283 Water masses
DE: 4924 Geochemical tracers
DE: 4938 Interhemispheric phasing
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005