Changes in oceanic oxygen isotope ratios (18O to 16O) are reflected in the shells of ancient foraminifera.

However, I have not read of diatom shells being used, despite the fact that they were (and are) at least as abundant, correct?

I know that diatoms use silica instead of calcium carbonate... Does that mean anything? Are diatoms using already-ancient sand to make their shells, rather than creating their own from newly-formed molecules, like foraminiferae do? Does that mean any CaCO3-using creature can be used as an ancient temperature proxy, since they always utilize the oxygen isotopes available in their time and place?

Can diatoms' remains be examined for any ancient information? They are so abundant...


1 Answer 1


Lacustrine diatoms are used extensively as reliable conventional proxies in Holocene (within the last 10,000 years) paleoclimate studies. According to this 2010 paper:

(paleoclimate) Reconstructions based on all these methods rely on the general assumption that the environmental requirements of the fossil diatom taxa used as bioindicators have remained constant during the period considered and, consequently, are similar to those of their closest living representatives. In this way, the environmental information obtained from living organisms can be used as modern analogous and extrapolated to the fossil record, particularly in Quaternary research

As abundant as they are in living form, diatoms are generally poorly (and unreliably) preserved in an older oceanic fossil record. Importantly, they evolve rather quickly making tracking chemical changes in a single species over time and space impossible. Bulk chemistries may be obtained from fossilized silicic masses and serve as rough indicators of overall diatom abundance and thus system health.

They are, however, used in novel ways: some diatoms live exclusively in sea ice and can be used to assess duration and distribution of that sea ice, itself a record of sea surface temperature (SST):

Diatoms in Arctic regions: Potential tools to decipher environmental changes

SIDEBAR. Diatoms as Sea Ice Proxies

By contrast, forams are well preserved in the fossil record, have a well calibrated evolutionary record, and as carbonates, contain important isotopes whose ratios are sensitive to SST.


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