Glacial-Interglacial Cycles in Biological Productivity and Nitrate Utilization in the Subantarctic Ocean During the Last 200 kyrs

The Subantarctic Ocean shows a well-known glacial-interglacial alternation in sediment composition. Coccolithophore-foraminifera dominance occurs during nutrient-depleted interglacial periods, whereas diatom dominance occurs during nutrient-rich glacial periods driven by nutrient inputs from the Antarctic Zone. However, the link between these biological changes and oceanographic/climatic variability remains poorly constrained. In this study, we investigate the mechanisms linking glacial-interglacial biological changes to oceanographic and climatic variability by reconstructing diatom and coccolithophore productivity, export production, dust input, and nutrient utilization over the past 200 kyr at IODP Site U1539 using biogenic opal, CaCO₃, TOC, TN, terrestrial fraction, and bulk δ¹⁵N records. Our results show glacial-interglacial contrasts; high CaCO₃ and low biogenic opal, TOC, TN, terrestrial fraction, and bulk δ¹⁵N values during interglacial periods and the opposite patterns during glacial periods. Increased nitrate utilization indicates enhanced glacial stratification in the Subantarctic Ocean. Increased diatom production at Site U1539 indicates relatively increased silicate supply from the Antarctic Zone. Despite enhanced stratification in the Antarctic Zone, the Antarctic Polar Front migrated northward during glacial periods. At the same time, decreased Si/N uptake (i.e., reduced silicate consumption) may have increased silicate supply to the Subantarctic Ocean. As diatom production and export production co-vary, export production was primarily controlled by diatom productivity. Thus, silicate supply from the Antarctic Zone controls glacial-interglacial diatom and export production, whereas nutrient utilization is more closely related to stratification and dust input.