Paleoceanographic changes in the Okhotsk Sea during the past 25,000 years - implications for ventilation of North Pacific intermediate water and stratification patterns.

Lembke-Jene, Lester, Tiedemann, Ralf, Nürnberg, Dirk , Bubenshchikova, Natalia and Dullo, Wolf-Christian (2011) Paleoceanographic changes in the Okhotsk Sea during the past 25,000 years - implications for ventilation of North Pacific intermediate water and stratification patterns. [Poster] In: AGU Fall Meeting 2011. , 05.12.-09.12.2011, San Francisco, California, USA .

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Abstract

ABSTRACT FINAL ID: PP41C-1794
Today’s knowledge about the past variability in North Pacific Intermediate Water (NPIW) formation and ventilation is still limited and rests largely on paleoceanographic time series from the eastern Pacific and regions distal to principal formation regions. Okhotsk Sea Intermediate Water (OSIW) is presumed to be the most important precursor for the formation of NPIW and is today also the main contributor to mid-depth ventilation in the North Pacific. Formation of OSIW at the northern Sakhalin margin is closely coupled to the basin's boundary conditions such as freshwater river discharge from the Amur and the dynamics of sea-ice.
Earlier works implied significant ventilation changes in the NW-Pacific during the Last Glacial Maximum (LGM) with a better ventilated North Pacific Intermediate Water (NPIW) compared to today, with a clear boundary to less-ventilated Pacific Deep Water masses around 2000 m.
In our study we used a comprehensive suite of more than 20 sediment cores along lateral and vertical transects to gain a good coverage of the basin and complement existing older data. We focused on intermediate water depths between 600 and 2000 m to better reconstruct the glacial ventilation history of OSIW. Our results show - contrary to earlier results - that no clear boundary can be defined between better and less well ventilated water masses at 2000 m water depth based on stable carbon isotope data of benthic foraminifera. Overall, the water column structure more resembles a vertically pattern similar to modern oceanographic conditions during the LGM, albeit overall slightly better ventilated than today. An upper part of better ventilated OSIW (700-1000 m) might stem from the inflow area near the Kamchatka continental margin.
For the Holocene, a smaller sub-set of gravity cores off the Sakhalin continental margin was chosen to investigate the history of rapid changes in the formation of OSIW. A high-resolution sediment core from the Kamchatka continental margin proximal to the inflow of NW-Pacific water masses completes our set. According to our AMS 14C-based age models, maximum sedimentation rates range from 30 to 160 cm/kyr, while average sample spacing varies between 5 and 150 years. Planktic and benthic foraminiferal δ18O data from the Sakhalin margin suggest a high variability in the formation of OSIW determined by large fluctuations in the discharged Amur’s freshwater volume, influencing the stratification of local surface water masses and formation of sea ice. The δ13C data of benthic foraminifera reveal that a principal mid-Holocene shift in surface and intermediate water hydrography occurred in the Okhotsk Sea around 4.5 kyr BP, with better OSIW ventilation during the late Holocene and intermittent cessation of ventilated OSIW during the early part. The shift of baseline conditions into a different state at 4.5 kyr BP was accompanied by significant changes in the frequency and amplitude of shorter-term centennial-scale variability in both upper mixed layer and intermediate waters in the Okhotsk Sea.

Document Type: Conference or Workshop Item (Poster)
Keywords: Paleoceanography; Oceanography; Marginal and semi-enclosed seas; Abrupt / rapid climate change; Glacial
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
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Date Deposited: 25 Jan 2012 15:07
Last Modified: 23 Feb 2012 05:40
URI: http://oceanrep.geomar.de/id/eprint/13583

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