MICRO-COMPUTED TOMOGRAPHY SCANNING OF FORAMINIFERA AS INDICATORS OF CALCITE COMPENSATION DEPTH CHANGE IN THE WESTERN SOUTH ATLANTIC DURING THE EOCENE-OLIGOCENE TRANSITION

The impact of anthropogenic climate change on the global carbon cycle necessitates research that better characterizes the effect of rapid climate events on ocean carbonate production, preservation, and storage. Using CT numbers from X-ray micro-Computed Tomography (CT) scans of planktic foraminifera to quantify carbonate dissolution as developed by Iwasaki et al. (2015, 2019) is a promising methodology; however, this approach has not yet been tested in deeper time using extinct planktic or benthic foraminifera species. The Eocene-Oligocene Transition was characterized by relatively rapid climate cooling and a global deepening of the calcite compensation depth. Thus, it represents an ideal time interval to test Iwasaki et al.’s approach on geological samples. Here, we present preliminary CT scans of planktic and benthic foraminifera from Site U1558, recently drilled during International Ocean Discovery Program Expedition 393 in the western South Atlantic Ocean. Our preliminary data indicate that micro-CT scanning of foraminifera can be useful in demonstrating changes in carbonate preservation in deep-sea sediments. Initial scans show a lower mean CT-number for the late Eocene specimen, indicating it contains more recrystallized calcite relative to the early Oligocene specimen. Although our results also show that diagenetic alteration of specimens can complicate the application of this method, evidence of this alteration is clearly visible in CT scans, providing a means of quality control for geochemical analyses on specimens with uncertain preservation. Despite these challenges, with further development the method should be a useful way to estimate variability in the calcite compensation depth as it provides a uniquely quantitative approach to relative changes in carbonate preservation through time.

Iwasaki, S., et al. (2019). Geochemistry, Geophysics, Geosystems, 20, 6051– 6065.

Iwasaki, S., et al. (2015). Paleoceanography, 30, 317– 331.