Spatiotemporal variation in burial characteristics of calcareous biogenic detritus in the northwestern Indian Ocean and the implication for deep-sea water dissolution

The preservation state of marine calcareous bioclasts during settling and burial in deep sea is a key indicator to the deep-sea carbonate dissolution and carbon cycling. Through a multi-proxy analysis of three sediment cores (Core 20, 21, 24) from water depths of 3716–4736 m in the northwestern Indian Ocean, including fragmentation ratio, elemental contents (Ca, Fe), calcium carbonate content, grain size, and color (L* value, gray level), the burial characteristics and main controlling mechanisms of calcareous bioclasts in shallow subsurface (0–2 m) sediments were revealed. Results show that: 1) The fragmentation ratio is positively correlated with water depth and dissolution intensity; it increases significantly with depth and exhibits marked variations within the same core, showing a strong negative correlation with calcium carbonate content. 2) Sediment lightness/darkness is related to the Ca/Fe ratio: high-calcium layers appear milky white with high L* values and low gray levels, indicating well-preserved shells under weak dissolution; high-iron layers are dark brown with low L* values and high gray levels, reflecting increased breakup under strong dissolution. 3) The fragmentation ratio shows millennial- to orbital-scale rapid fluctuations, suggesting that the deep-sea dissolution in this region was driven by changes in primary productivity or ocean convection. This study provided high-resolution sedimentological evidence for understanding deep-sea carbon cycling and paleo-oceanographic environmental evolution in the area.