Physical Properties and Their Relation to High Frequency Climate Change as Recoded by IMAGES Cores From the Labrador Sea

Abstract

Records of surface-water isotopic composition in the Labrador Sea (IMAGES cruises MD101 and MD99) show high-frequency climate change signals during the last glacial cycle and all Heinrich events and several major Dansgaard-Oeschger cycles. The same high-frequency climate change is documented for deep-water processes by peaks of physical and optical properties that mainly describe changes in sediment composition. Heinrich events are marked by light $\delta$$^{18}$O values of N. pachyderma and highs in density, velocity, and magnetic susceptibility. Thus, the variation of surface-$\delta$$^{18}$O values of all sites can be either predicted from core logging using the procedure developed at reference site 2024, or it can be derived site-specifically by incorporating $\delta$$^{18}$O measurements of individual cores. Both prediction and derivation provide a paleoclimate proxy record at unprecedented resolution. Physical property logs of Labrador Sea sediments represent deep-water processes rather than reflecting variable input of IRD or biogenic components. Deep-water origin of log signals is inferred from grain-size analysis, benthic $\delta$$^{18}$O, the relation of density and velocity, and magnetic susceptibility considerations. As for grain-size distribution, for example, highs in physical properties correspond to larger amount of sortable silt, a clear indication of faster deepwater currents during times of light surface-water $\delta$$^{18}$O values. These times also correspond to higher air temperature over Greenland. The close correlation of $\delta$$^{18}$O in ice, surface-water $\delta$$^{18}$O, and core logs implies a strong link and common forcing of atmosphere, sea surface, and deep water; yet the nature of this forcing is unknown. Variations in current strength along the west coast of the Labrador Sea are ultimately related to the production of NADW. Variable strength of bottoms currents is also reconstructed from changes in the relative amount of magnetic material. Times of non-correlation between core log and surface-water $\delta$$^{18}$O contain a climate signal of decoupling of forcing factors; e.g., during times of substantial sea-level rise, surface-water $\delta$$^{18}$O values changed dramatically, whereas deep-water properties did not. The varying extent to which core logs from different locations correlate to surface-water $\delta$$^{18}$O values, describes differences in deep-water processes among sites; e.g., the current velocity at site 2025 was apparently higher than at site 2024, an interpretation that is substantiated by the observation that site 2025 is presently located closer to the water depth of the high-velocity core of NADW.

Department

Center for Coastal and Ocean Mapping

Publication Date

2000

Volume

81, issue 48

Journal Title

Fall Meeting, American Geophysical Union (AGU)

Conference Date

Dec 15 - Dec 19, 2000

Publisher Place

San Francisco, CA, USA

Publisher

American Geophysical Union Publications

Document Type

Conference Proceeding

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