Decoupling of surface productivity and organic carbon preservation in the southeastern Arabian Sea during the last two glacial-interglacial cycles

Marine organic carbon burial is a fundamental regulator of global biogeochemical cycle, yet the vast majority of surface production is remineralized before long-term sequestration. Understanding this non-linear relationship between production and preservation in past is vital in understanding the carbon dynamics in ocean. Here, we investigate the relationship between surface productivity and sedimentary organic carbon preservation using a multiproxy record from sediment core SSD004 GC11 in the southeastern Arabian Sea spanning the last ∼167 kyr. We combine total organic carbon (TOC), Globigerina bulloides relative abundance, δ 13 C org , TOC/TN, Cibicidoides wuellerstorfi δ 13 C and benthic foraminiferal assemblages with model simulations and published regional deep-water circulation records. The G. bulloides record indicates substantial variability in upwelling, broadly associated with changes in monsoon-related zonal winds and precession. In contrast, residual TOC shows additional enrichment during several glacial and stadial intervals that is not proportional to the productivity signal. Quantitative comparison of TOC and G. bulloides identifies substantial TOC variability, particularly during MIS 2, MIS 4 and MIS 6. These intervals are accompanied by more negative C. wuellerstorfi δ 13 C values and increased abundance of angular asymmetrical benthic foraminifera, consistent with enhanced oxygen-depleted southern-sourced deep-water intrusion during stadials. Our results demonstrate that surface productivity and sedimentary organic carbon enrichment respond to partly independent controls on glacial-interglacial timescales, highlighting the importance of deep-water ventilation in modulating organic carbon preservation potential in the southeastern Arabian Sea. Furthermore, our results underscore the role of Indian Ocean as the carbon reservoir during the glacial periods and its subsequent feedback to the global climate system.