Arctic Ocean Temperature History since 60 ka based on ostracode Mg/Ca ratios
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-...
| Main Authors: | , , , , , , , |
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| Format: | Conference Object |
| Language: | unknown |
| Published: |
2011
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| Subjects: | |
| Online Access: | https://oceanrep.geomar.de/id/eprint/13078/ http://www.geogr.msu.ru/structure/labs/notl/nauchd/downloads/Abstracts_2011_APEX_Longyearbyen.pdf |
| Summary: | 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 ... |
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