Arctic Ocean Temperature History since 60 ka based on ostracode Mg/Ca ratios.

Cronin, T. M., Dwyer, G. S., Briggs, W. M. Jr., Farmer, J., Bauch, Henning A., Jakobsson, Martin, Spielhagen, Robert F. and Stepanova, Anna (2011) Arctic Ocean Temperature History since 60 ka based on ostracode Mg/Ca ratios. [Talk] In: APEX Fifth International Conference and Workshop: Quaternary Glacial and Climate Extremes. , 01.06.-04.06. 2011, Longyearbyen, Svalbard, Norway . APEX Fifth International Conference and Workshop: Quaternary Glacial and Climate Extremes / hosted by The University Centre in Svalbard (UNIS). ; pp. 57-58 .

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Proxy records from Arctic Ocean sediment cores show that major paleogeographic changes occurred during the last glacial-interglacial cycle, but there is minimal data on Arctic Ocean temperature history. Mg/Ca ratios in the calcitic shells of Krithe, a benthic marine ostracode characteristic of deep-sea and Arctic
continental shelf environments, have been used to reconstruct bottom water temperature (BWT) in the North Atlantic (Dwyer et al. 1995, Cronin et al. 1996). We analyzed Mg/Ca and Sr/Ca ratios in more than 500 specimens of K. glacialis and K. minima from 114 coretops in the Arctic Ocean and Nordic Seas to improve the Mg/Ca–temperature calibration and to evaluate the influence of other factors on Mg/Ca and Sr/Ca ratios (e.g. vital effects, carbonate ion concentration). Mg/Ca concentrations range from 6 to 13 mmol/mol and exhibit a positive correlation to temperature from -1.5 to 0.5ºC (r
2=0.4) with a sensitivity of 0.471 mmol/mol/ºC. Temperature, or temperature-related factors affecting physiology, molting and/or calcification processes, appear to be an influence on Mg/Ca variability. Carbonate ion shows no apparent relationship to Mg/Ca at ∆[CO3-2] values from -20 to 70 μmol/kg, however Sr/Ca ratios are positively correlated to ∆[CO3-2] (r2=0.5).
We applied Mg/Ca paleothermometry for K. glacialis and K. minima to 32 sediment cores from the central Arctic Ocean (Lomonosov, Mendeleyev, Gakkel Ridges) and the Iceland Plateau. Marine Isotope Stage 3 (MIS3, 60-25 ka) Mg/Ca ratios at mid-depth sites (1000-2600 m water depth) average 2 to 8 mmol/mol higher than those in the late Holocene suggesting MIS3 BWTs were 1-3 ̊C warmer. In contrast, at core sites below 3000 meters, Mg/Ca ratios indicate little or no BWT change during MIS 3. Warmer mid-depth MIS 3 BWTs are consistent with oxygen isotope evidence for glacial-age elevated BWTs in the Iceland Sea (Bauch t al. 2001). Mid-depth Arctic Ocean warming most likely involves changes in the depth, circulation or temperature of the warm Atlantic Layer (AL). Possible mechanisms include AL depth suppression due to ice cover (Jakobsson et al. 2010) and/or higher AL temperatures due to enhanced Atlantic Meridional Overturning Circulation. Hypothesized elevated Arctic and Nordic Sea MIS3 BWTs can be tested against other proxies, with better radiocarbon chronology to determine if BWT warming occurred during interstadials or stadials, and in comparison to extra-Arctic paleoclimate records.

Document Type: Conference or Workshop Item (Talk)
Keywords: Polar Research; Paleoceanography
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Projects: Polynya, Laptev Sea System
Date Deposited: 19 Dec 2011 10:36
Last Modified: 19 Dec 2014 10:43

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