Ocean temperature 120 million years ago
Ocean temperature 120 million years ago
The oxygen isotopic compositions of fossil foraminifera tests constitute a continuous proxy record of deep-ocean and sea-surface temperatures spanning the last 120 million years. Here, by incubating foraminifera tests in 18O-enriched artificial seawater analogues, we demonstrate that the oxygen isotopic composition of optically translucent, i.e., glassy (apparently unaltered), fossil foraminifera calcite tests can be measurably altered at low temperatures through rapid oxygen grain-boundary diffusion without any visible ultrastructural changes. Grain boundary diffusion can be shown to bias prior paleotemperature estimates by as much as plus or minus half a degree or nearly one degree centigrade.
Figure: Temperature biases due to grain boundary diffusion in fossil benthic and planktonic foraminifera tests (the left y-axis shows the temperature bias induced by grain boundary diffusion on existing seawater paleotemperature reconstructions; foraminifera δ18OLattice−δ18OBulk, shown on the right y-axis). On the right: ventral sides of pristine and hydrothermally incubated Ammonia sp. tests (no difference can be seen).
PUBLICATION: Adams, A., Daval, D., Baumgartner, L.P., Bernard, S., Vennemann, T., Cisneros-Lazaro, D., Stolarski, J., Baronnet, A., Grauby, O., Guo, J., Meibom, A. 2023. Rapid grain boundary diffusion in foraminifera tests biases paleotemperature records. Communications Earth & Environment 4:144, doi:10.1038/s43247-023-00798-2
