213 Cushman Symposium: Microfossils of Extremophiles: Living in the Danger Zone

This session will assemble studies documenting microfossil presence and/or microfossil-generating taxa in extreme environments, widely defined present and past, and those elucidating adaptations employed by extremophiles, to inform interpretations of the geologic record.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 303C

Constraining the habitat of Globorotaloides hexagonus, a low-oxygen affiliated planktic foraminifera

Paper number: 213-7
Program: Technical Sessions
Time: 3:10 PM – 3:30 PM

Authors

Abstract

The extant microfossil-forming foraminifer, Globorotaloides hexagonus, has been widely associated with low-oxygen waters, where it is apparently adapted to tolerate dysoxic to anoxic conditions. As a result, G. hexagonus shells (tests) represent a promising target for paleoceanographic reconstructions, with the occurrence of their shells reflecting the presence of low-oxygen pelagic waters. Such inferences will become more robust as the habitat and ecology of G. hexagonus is better constrained. Here we present the distributions of G. hexagonus collected in discrete-depth MOCNESS tows (222 and 150 μm mesh) from between the surface and 1000-m water depth from three sampling campaigns in the Eastern Tropical North Pacific and along the northeastern Pacific margin. Cytoplasm-containing G. hexagonus were recovered from water-column strata with as little as 1 μmol L-1 ambient O2. The greatest standing stocks of G. hexgaonus across all campaigns were found in nets sampling the lowest O2 levels (<10 μmol L-1), but the species occurs with some frequency in waters up to ~80 μmol L-1. We hypothesize that G. hexagonus occupies this relatively wide range of low [O2] by embedding itself in aggregates of organic detritus to maintain a consistently low-oxygen microenvironment. We moreover affirm the utility of G. hexagonus as a paleo-oxygen indicator and suggest that recovery of G. hexagonus shells could be considered a strong indication of water with O2 values equal to or below 80 μmol L-1 having been present in the water column.

 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412136

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