Temporal, Morphological, and Taxonomic Frameworks for Calibrating Benthic Foraminiferal Pore Patterns as a Paleoxygenation Proxy

Calcareous benthic foraminifera commonly develop pores in their test wall for gas exchange (e.g., O2, CO2) with seawater. Pore patterns, that is, porosity, pore density, and pore size, are influenced by environmental factors like bottom water dissolved oxygen concentration (BWDO). Certain benthic foraminifera species show increased test porosity under low BWDO, making them a useful proxy for reconstructing past BWDO. The pore patterns as a proxy for BWDO are validated in the Southeast Pacific (SEP) by examining six benthic foraminifera species in relation to estimated BWDO on the sediment sites. Specimens were collected from surface sediments between 24 and 3,252 m water depth across the SEP (12°–44°S). Specimens were selected based on their Rose Bengal staining, oxygen isotopes, and calibrated sediment radiocarbon age to reflect modern conditions. Porosity, pore density and size were measured on the umbilical and spiral sides of the foraminifera, including all visible chambers, and the penultimate and antepenultimate chambers (PAC). Pores on the umbilical side, facing the water column, and the spiral side, commonly used for attachment, are measured to test their response to changes in oxygen uptake. In the SEP, the strongest correlations between BWDO and porosity is found for measurements from the umbilical side of the benthic foraminiferal test, indicating that this area is the most sensitive to BWDO changes. Combined benthic foraminifera species, and C. wuellerstorfi, increase umbilical porosity under lower BWDO. These findings align with global calibrations, supporting the quantitative use of benthic foraminifera pore patterns to reconstruct past BWDO, with an error range of around ±60 μmol kg−1 for BWDO above 100 μmol kg−1, and around ±20 μmol kg−1 for lower than 100 μmol kg−1.