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| Titel |
Planktonic foraminiferal Mg/Ca ratios: How a temperature proxy becomes an indicator of global bottom water calcite-saturation states |
| VerfasserIn |
Marcus Regenberg, Anke Dürkop, Dieter Garbe-Schönberg |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043620
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| Zusammenfassung |
| The effect of the calcite-saturation state of bottom waters, which is defined as difference
between the in situ carbonate concentration and the carbonate concentration at saturation, on
the preservation of carbonates in sediments is still under debate. Estimates of carbonate
preservation to reconstruct the relative vertical position of a sample with respect to the
lysocline depth are often based on properties of the bulk sediment (e.g., carbonate content,
colour, coarse-to-fine fraction ratio), which are also controlled by processes at the
sea surface. Additionally, such relative positions were derived from planktonic
foraminiferal fragmentation (i.e. the proportion of fractured foraminiferal tests
due to dissolution-induced calcite thinning related to the relative position of the
lysocline). A quantitative indicator of the calcite-carbonate state, however, will be
introduced here. We present a study on tests of ten planktonic foraminiferal species
from various sediment-surface samples exposed to bottom waters characterized by
supersaturation through undersaturation with respect to calcite. Our data reveal that above a
calcite-saturation state of -20 μmol/kg, planktonic foraminiferal Mg/Ca ratios are unaltered
compared to their primary signal, which was recorded during test formation at
similar calcification temperatures. Below -20 μmol/kg, Mg/Ca ratios linearly
decrease with decreasing calcite-saturation states. Similar effects of dissolution on
multispecies Mg/Ca ratios from the fairly supersaturated tropical Atlantic as well as from
the much more corrosive tropical Pacific suggest planktonic foraminiferal Mg/Ca
ratios to be a globally valid indicator of bottom water carbonate-saturation states. |
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