A large glacial-interglacial shift in carbon burial in the northeast Indian Ocean during the Late Quaternary

Carbon is a common element on Earth, found in various molecular forms. However, the excessive release of carbon dioxide (CO₂) into the atmosphere from burning fossil fuels is a major concern due to its greenhouse potential. The oceans help remove a significant amount of atmospheric CO₂ through organic (C_org) and inorganic carbon (CaCO₃) sequestration, burying it in sediments for a long time. The ocean's ability to store carbon varies with time, depending on several factors, making it challenging to predict the future fate of atmospheric CO₂. The northeast Indian Ocean is particularly vulnerable to human activities that could alter its potential to store carbon in the bottom sediments. Therefore, it is crucial to understand how carbon burial has changed in this region over time. We provide basin scale changes in carbon burial in the northeast Indian Ocean by using organic carbon (C_org %), calcium carbonate (CaCO₃ %), total carbon (TC), organic carbon to nitrogen ratio (C_org/N), stable carbon (δ¹³C) and, nitrogen (δ¹⁵N) isotopic ratio data from a total of 19 cores (3 new and 16 previously published). We report a significant change in carbon burial in both the marginal marine and open ocean regions of the northeast Indian Ocean during glacial-interglacial intervals. Additionally, different regions of the ocean stored varying amounts of carbon, indicating a strong spatial heterogeneity in carbon burial since the last deglaciation. During the last glacial maximum (LGM), sediments' CaCO₃ content decreased in the deep sea but increased on the shelf. The opposite was true for C_org burial patterns, with values higher than recent throughout the LGM, and the highest C_org content during LGM. The basin-wide lowest CaCO₃ and C_org content was during the Greenlandian and Northgrippian. Marginal seas' carbon burial changes were mainly influenced by monsoon-induced productivity, sedimentation rate, sediment texture, and dissolved oxygen concentration. On the other hand, water mass changes primarily drove carbon burial in deeper regions. The findings will help in assessing the carbon burial potential of this region in the warming world.