Contrasts in calcium carbonate dissolution above the lysocline in the equatorial Indian Ocean over the last ~40 ka

Abstract

Understanding calcite dissolution above the lysocline is crucial to comprehend the oceanic calcium carbonate cycle. To understand past calcite dissolution in sediments from above the lysocline, we use multiple dissolution proxies in a gravity core SSD-44/GC-01 from the central equatorial Indian Ocean, which spans a period of 43 ka. Our results suggest that calcite dissolution occurred during marine isotope stage −3 (MIS-3) and the last glacial maximum (LGM). Furthermore, dissolution of carbonate with increasing intensity occurred during the Holocene. Calcite dissolution above the lysocline is probably a result of pore water undersaturation in carbonate ion, which is in line with increased productivity during MIS-3 and the LGM. Furthermore, decreased sedimentation rate and increased exposure time of foraminifera during the Holocene may have led to efficient organic matter degradation and pore water undersaturation in carbonate ion. However, better preservation of calcite observed during the last deglacial period is probably due to increased deep-sea carbonate ion concentration, related to outgassing of CO2 to the atmosphere, stored during the LGM in the deep sea.