Millennial-scale climate variability in the subarctic NW-Pacific during the last 150 kyr and implications for upper-ocean stratification.

Riethdorf, Jan-Rainer, Max, Lars, Nürnberg, Dirk , Tiedemann, Ralf, Gorbarenko, Sergey and Malakhov, Mikhail (2011) Millennial-scale climate variability in the subarctic NW-Pacific during the last 150 kyr and implications for upper-ocean stratification. [Talk] In: AGU Fall Meeting 2011. , 05.12.-09.12.2011, San Francisco, California, USA .

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Abstract

ABSTRACT FINAL ID: PP52A-05
The N-Pacific and its marginal seas are thought to hold an important key for understanding the processes of Pleistocene changes in oceanic-atmospheric gas exchange, which are related to variations in upper ocean stratification, sea ice distribution, marine productivity, nutrient consumption, deep water formation and laminae formation. However, the shallow carbonate lysocline within the N-Pacific realm limits the library of proxies for reconstructing such changes in space and time.
Here, we present sediment records from the western Bering Sea, recovered on a north-south transect from intermediate water levels above the lysocline, allowing for the application of carbonate-based proxies. The age models are based on a combination of different tools including benthic oxygen isotope stratigraphy, paleomagnetics and AMS14C-datings. In addition, high-resolution spectrophotometric measurements (color b*) and XRF-scans provide a pattern of variability that strongly corresponds to the Daansgaard-Oeschger climate variability registered in the NGRIP ice core record. This remarkable correlation suggests a close atmospheric coupling between Greenland and the N-Pacific.
We assess past changes in marine productivity and terrigenous fluxes by high-resolution XRF-element scanning and measurements of TOC, CaCO3 and biogenic opal. Results show distinct changes between warm and cold stages during the last 150 kyr as well as clear trends along the north-south
transect. Cold stages (MIS2, MIS4, MIS5d, MIS6) are characterized by high sedimentation rates (LSR), large amounts of siliciclastics, and high contents of typically lithogenic elements Al, Fe and Ti. Accumulation of CaCO3 and TOC is increased as well while that of biogenic opal is low. The latter points towards prohibited primary productivity in the western Bering Sea, dominated by diatoms, possibly due to a (perennial) sea-ice coverage. Warm stages (MIS1, MIS3, MIS5) show an exactly reversed situation suggesting enhanced surface water productivity under ice-free conditions. Remarkably, interstadials are mirrored by maxima in Ca/Ti and Ba/Al ratios, and minima in Si/Sr ratios. The amount of coarse material (>63 μm), considered as a result of sea ice melting, shows distinct maxima during deglaciations only, while Al/Ti and C/N ratios as terrigenous source indicators remain fairly constant even on the glacial-interglacial level. This further indicates that sea ice formation is the primary transport mechanism for terrigenous matter.
Sea surface temperatures are reconstructed for the last 20 kyr using alkenones and planktonic foraminiferal Mg/Ca ratios. Results show that a temperature gradient develops within the upper water column at the onset of the Holocene. We interpret this as the establishment of a permanent halocline which led to an intensification of upper-ocean stratification, probably occurring 2-3 ka later than in the Sea of Okhotsk.

Document Type: Conference or Workshop Item (Talk)
Keywords: Paleoceanography; Climatology; Glacial; Interglacial; sea-surface temperature
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
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Date Deposited: 09 Jan 2012 10:48
Last Modified: 23 Feb 2012 05:36
URI: http://oceanrep.geomar.de/id/eprint/13095

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