Organic carbon preservation in Southeastern Arabian Sea sediments since mid‐Holocene: Implications to South Asian Summer Monsoon variability

The earlier studies show a contrasting long-term trend of the South Asian Summer Monsoon (SASM) after attaining the precessional forcing induced mid-Holocene maximum. The increasing total organic carbon (TOC) concentration of marine sediments in the Southeastern Arabian Sea (SEAS) has been interpreted to imply strengthening SASM since mid-Holocene by a few studies. However, TOC concentration is also influenced by redox conditions, sedimentation rate, and an influx of terrigenous matter depending on the regional settings. So, it needs to be ascertained whether the TOC concentration of the sediments in the SEAS is a signal of productivity related to the SASM strength or preservation. Therefore, we studied multiple proxies (TOC, total nitrogen, atomic C/N, δ13Corg, CaCO3, and major and trace elements concentration) for determining the productivity, redox conditions, detrital supply, and provenance in a sediment core from the upper continental slope of the SEAS spanning the past ∼4700 years at centennial scale resolution. The present study shows that the observed TOC increase is not a result of enhanced productivity but is because of better preservation due to the increased sedimentation rate along with increasingly reducing conditions since mid-Holocene. We further show that the SASM has been declining since mid-Holocene after attaining a precession-forced maximum, which corroborates the earlier model ensemble studies.