In:
Biogeosciences, Copernicus GmbH, Vol. 16, No. 10 ( 2019-05-20), p. 2115-2130
Abstract:
Abstract. Shell chemistry of foraminiferal carbonate proves to be
useful in reconstructing past ocean conditions. A new addition to the proxy
toolbox is the ratio of sulfur (S) to calcium (Ca) in foraminiferal shells,
reflecting the ratio of SO42- to CO32- in seawater. When
comparing species, the amount of SO42- incorporated, and therefore
the S∕Ca of the shell, increases with increasing magnesium (Mg) content. The
uptake of SO42- in foraminiferal calcite is likely connected to
carbon uptake, while the incorporation of Mg is more likely related to Ca
uptake since this element substitutes for Ca in the crystal lattice. The
relation between S and Mg incorporation in foraminiferal calcite therefore
offers the opportunity to investigate the timing of processes involved in Ca
and carbon uptake. To understand how foraminiferal S∕Ca is related to Mg∕Ca,
we analyzed the concentration and within-shell distribution of S∕Ca of three
benthic species with different shell chemistry: Ammonia tepida, Bulimina marginata and Amphistegina lessonii. Furthermore, we
investigated the link between Mg∕Ca and S∕Ca across species and the
potential influence of temperature on foraminiferal S∕Ca. We observed that
S∕Ca is positively correlated with Mg∕Ca on a microscale within specimens, as
well as between and within species. In contrast, when shell Mg∕Ca increases
with temperature, foraminiferal S∕Ca values remain similar. We evaluate our
findings in the light of previously proposed biomineralization models and
abiological processes involved during calcite precipitation. Although all
kinds of processes, including crystal lattice distortion and element
speciation at the site of calcification, may contribute to changes in either
the amount of S or Mg that is ultimately incorporated in foraminiferal
calcite, these processes do not explain the covariation between Mg∕Ca and
S∕Ca values within specimens and between species. We observe that groups of
foraminifera with different calcification pathways, e.g., hyaline versus
porcelaneous species, show characteristic values for S∕Ca and Mg∕Ca, which
might be linked to a different calcium and carbon uptake mechanism in
porcelaneous and hyaline foraminifera. Whereas Mg incorporation might be
controlled by Ca dilution at the site of calcification due to Ca pumping, S
is linked to carbonate ion concentration via proton pumping. The fact that
we observe a covariation of S and Mg within specimens and between species
suggests that proton pumping and Ca pumping are intrinsically coupled across
multiple scales.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-16-2115-2019
DOI:
10.5194/bg-16-2115-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2158181-2
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