Proxy development and application

Assessing the effect of dissolution on planktonic foraminiferal Mg/Ca ratios

Main conclusion: Depending on the foraminiferal species, Mg/Ca starts to decline linearly below ΔCO3

2- levels of 18-26 µmol/kg. Above these critical levels, Mg/Ca remains stable. As these values hold for both Caribbean and Timor seas, we speculate that they are globally valid.

Project leadership: MS Student: D. Nürnberg (IFM-GEOMAR) A. Erichsen (IFM-GEOMAR) M. Regenberg (IFG Kiel)

Fig. 2 Foraminiferal Mg/Ca vs. ΔCO32-. Blue symbols = Caribbean

core-tops, red symbols = Timor Sea symbols. Horizontal bar indicates critical level, where Mg-removal starts.

Although foraminiferal Mg/Ca is widely applied to reconstruct paleo-seasurface temperature, the effect of calcite dissolution and the selective removal of Mg from the foraminiferal calcite is not satisfactorily studied. We here studied various planktonic foraminiferal species (see below) from Caribbean and Timor Sea core-top sediments to show the effect of the calcite saturation state (expressed as ΔCO3

2-) on foraminiferal Mg/Ca.

Fig. 1. Study areas in the Caribbean and in Timor Sea

-10

0

10

20

30

40

50

3 3.5 4 4.5 5

G. sacculifer

Mg/Ca (mmol/mol)

ΔC

O3 2-

(µm

ol/k

g)

N. dutertrei G. sacculifer G. truncatu- linoides

G. ruber G. tumida G. menardii G. crassa- formis

G-cubed, 2006