Deep-water nutrients mediated glacial-interglacial diatom productivity in the Indian Polar Front Zone of the Southern Ocean

High diatom blooms characterize the Crozet and Kerguelen Plateaus of the Southern Ocean (SO) due to the natural iron fertilization despite the co-limitation of iron and light in the Polar Front Zone (PFZ). However, information on glacial-interglacial diatom productivity and associated biological carbon pump from this region is sparse. We present a diatom productivity record to decipher the palaeoceanographic changes for the past 40 ka using sediment core SN ₂ (47°S and 57°30’E) amidst the Crozet and Kerguelen Plateau. Our results show the highest diatom productivity during early Marine Isotope Stage (MIS) 2 (29.5–23 ka), lowest during the deglacial-Holocene periods (18 − 7.8 ka), with lower intermediate diatom productivity during late MIS 3 (40-29.5 ka) and the Last Glacial Maximum (LGM, 23 − 18 ka). The abundances of the permanent open ocean zone (POOZ) group diatoms covaried with diatom productivity and showed an inverse correlation with water stratification group diatoms. The patterns of diatom productivity and the POOZ group diatoms do not strongly correlate with the fluxes of dust and iron. Based on the inverse correlation between the diatom groups from the PFZ (core SN ₂ ) and the Antarctic zone, we suggest that higher diatom productivity during early MIS 2 could be due to the availability of nutrient-rich southern waters through SO upwelling as a result of the northward Antarctic Polar Front (APF) migration. Conversely, the lower intermediate diatom productivity during late MIS 3, the LGM, and the deglacial-Holocene periods could have resulted from the unavailability of southern nutrient-rich waters due to inefficient APF migration and weaker SO upwelling. We propose that the Antarctic Circumpolar Current-driven APF migration and the intensity of upwelling possibly resulted in heterogeneous diatom productivity in the Indian PFZ of the SO. Consequently, the availability of deep-water nutrients (iron and silicate) might have controlled diatom productivity and was responsible for the strengthening/weakening of the biological carbon pump.