Further constraints on the diagenetic influences and salinity effect on Globigerinoides ruber (white) Mg/Ca thermometry: Implications in the Mediterranean Sea

Anna Sabbatini, Franck Bassinot, Soumaya Boussetta, Alessandra Negri, Hélène Rebaubier, Fabien Dewilde, Julius Nouet, Nicolas Caillon, Caterina Morigi

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    18 Citations (Scopus)

    Abstract

    We analyzed Mg/Ca ratios of the planktonic species Globigerinoides ruber (white) picked from 49 box core samples covering the whole Mediterranean Sea and 2 core tops from the Atlantic Ocean. Over the entire data set, we found no significant correlation between Mg/Ca and δ18O-derived calcification temperatures. This lack of correlation is chiefly due to the presence of an early diagenetic, Mg-rich calcite coating, which can constitute up to 20% of the total shell calcite in the central and eastern Mediterranean basin and result in anomalously high Mg/Ca values and a high scattering. In the western Mediterranean Sea, however, G. ruber Mg/Ca scattering shows smaller amplitude and Mg-rich calcite remains under the XRD detection limit. SEM observations indicate that only a few samples are affected by trace amounts of post-mortem calcite overgrowths (most of this calcite being likely removed during the chemical cleaning for Mg/Ca analyses). Using core top sediments from the western Mediterranean Sea, we performed an empirical calibration exercise, which confirms that G. ruber Mg/Ca is not only related to temperature but it is also significantly affected by sea surface salinity. This salinity effect is not specific to high salinity environments such as the Mediterranean Sea, since it appears to be coherent with recent results obtained on Indo-Pacific and Atlantic surface sediments, which suggest that a +1 (psu) change in SSS results in a +1.7°C Mg/Ca-temperature bias. This sensitivity to salinity is significantly higher than those deduced from culture experiments.
    Original languageEnglish
    Article numberQ10005
    Number of pages19
    JournalGeochemistry, Geophysics, Geosystems
    Volume12
    Issue number10
    DOIs
    Publication statusPublished - 1 Oct 2011

    Keywords

    • early diagenetic calcite coating
    • foraminiferal Mg/Ca
    • Mediterranean Sea
    • salinity

    Programme Area

    • Programme Area 3: Energy Resources

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