Temporal, morphological, and taxonomic frameworks for calibrating benthic foraminifera pores patterns as a proxy for paleoxygenation in the Southeast Pacific

Calcareous benthic foraminifera can develop pores in their shells for gas exchange with seawater. Pore patterns, like porosity, pore density, and pore size, are influenced by environmental factors like bottom water dissolved oxygen concentration (BWDO). Some benthic foraminiferal species increase their test porosity under low BWDO, making them a useful proxy for reconstructing past oxygenation. The pore patterns proxy for BWDO is validated in the Southeast Pacific (SEP) by examining six benthic foraminifera species compared to estimate BWDO on the sediment sites. Specimens were collected from surface sediments at 24–3,252 m water depths across the SEP (12°–44°S) and selected based on their Rose Bengal staining, oxygen isotopes, and calibrated sediment radiocarbon age to reflect modern conditions. The benthic foraminiferal species measured in this study typically have a planispiral shell with pores on two sides: pores on the umbilical side, which faces the water column, and the spiral side, commonly used for attachment. Both sides are measured to test their role in oxygen uptake. Porosity, pore density, and size were measured on all visible chambers and, specifically, on the penultimate and antepenultimate chambers. In the SEP, the main response to BWDO changes occurs on the umbilical side of the benthic foraminifera, while some oxygen uptake might also happen on the spiral side. Combined benthic foraminifera species, and solely C. wuellerstorfi, increase umbilical porosity under lower BWDO. These findings align with global calibrations, supporting the quantitative use of the benthic foraminifera pore patterns proxy to reconstruct past BWDO in other oceans, with an error range of around ±60 µmol kg^-1 for BWDO above 100 µmol kg^-1 and around ±20 µmol kg^-1 for BWDO lower than 100 µmol kg^-1.