Glacial rapid variability in deep-water temperature and d18O from the Western Mediterranean Sea

Cacho, I. and Shackleton, N. J. and Elderfield, H. and Sierro, F. J. and Grimalt, J. O. (2006) Glacial rapid variability in deep-water temperature and d18O from the Western Mediterranean Sea. Quaternary Science Reviews, 25 (23-24). pp. 3294-3311. DOI

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Abstract Deep-water temperatures (DWTs) from the Western Mediterranean Sea are reconstructed for the last 50 ka based on the analysis of Mg/Ca ratios in benthic foraminifera from core MD95-2043 collected in the Alboran Sea. The exceptionally high sedimentation rates of this core and the robust chronology available allow discussion of the results in the context of the Dansgaard–Oeschger (D–O) rapid climatic variability. The applicability of Mg/Ca thermometry in the Western Mediterranean Deep-Water mass (WMDW) is first tested by the analysis of different benthic species in a collection of Mediterranean core tops. The results indicate the need of a readjustment of the existing Cibicidoides spp. calibrations in order to reconstruct present Western Mediterranean DWT values (12.7 1C). Different physiological effects in the Mg uptake between the C. pachydermus living in different regions could account for this offset in the Mediterranean samples. Consequently, the obtained DWT record still has many uncertainties in absolute terms but trends provide valuable information on past changes in WMDW conditions. The DWT record shows significant oscillations in relation to the D–O cycles, colder values occurred during the time of D–O stadials and warmer ones during D–O interstadials. Surprisingly, the coldest DWTs occurred during the time of Heinrich Event 4 (HE4) and not during the Last Glacial Maximum (LGM) when DWTs were mostly warm. These and other particular features of the DWT reconstruction mimic changes in the vegetation from the Eastern Mediterranean indicating the control of the Mediterranean climate on the DWT record. Paired analyses of Mg/Ca and d18Occ (calcite d18O) provide the opportunity to reconstruct deep-water d18O (d18Odw) and past salinities and hence changes in past WMDW density. Due to the large error associated with these calculations, they can only be discussed in terms of relative changes between different intervals. The results suggest the dominance of a heavier water end member during glacial times and a lighter one during the early Holocene in relation to the d18Odw conditions present today. Densest WMDW were formed during most of Marine Isotopic Stage (MIS) 2 and during the D–O Stadials not associated with HEs, while lightest WMDW dominated during D–O Interstadials. The d18Odw record shows a D–O variability pattern likely controlled by changes in the composition and intensity of the local run-off and also to changes in the d18Ow signal of the Atlantic inflow. Changes in the residence time of the Mediterranean waters, governed by the global sea level, are also considered to exert an important role governing Mediterranean d18Ow and salinity, particularly during MIS 2. Overall, our results are consistent with the formation of dense WMDW during D–O stadials and even denser during most of MIS 2.

Item Type: Article
Uncontrolled Keywords: 2007 AREP IA53 2006 P
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Quaternary Science Reviews
Volume: 25
Page Range: pp. 3294-3311
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:01
Last Modified: 23 Jul 2013 10:01

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