Burial records of terrestrial organic carbon controlled by sea-level and monsoon variability in the Gulf of Thailand since the last deglaciation

Abstract

The sequestration of terrestrial organic carbon (OC_terr) exported from adjacent continent into marginal sea plays a critical role in the global carbon cycle over geological timescale. However, the processes controlling OC_terr burial in tropical coastal margins, particularly in response to sea-level and climatic changes, remain poorly understood. This study investigates millennial-scale OC_terr burial since the last deglaciation (∼14,640 years before present) in the Gulf of Thailand on the Sunda Shelf, Southeast Asia. By analyzing AMS¹⁴C, bulk organic carbon indicators (TOC/TN ratios, δ¹³C), and lipid biomarkers (e.g., n-alkanes), our results show that OC_terr dominated during last deglaciation (with meltwater pulses), coinciding with high OC_terr accumulation rates and a prevalence of herbaceous plants. Following the transgression phase, OC_terr sharply decreased to ∼20 % as sea level rose. The burial of OC_terr was modulated by high sedimentation rates, driven by rainfall associated with the East Asia Summer Monsoon, Indian Summer Monsoon, and Western Pacific warm Pool during the high sea-level stage. The evolution and burial of OC_terr in the northern Sunda Shelf since the last deglaciation have been primarily regulated by relative sea-level changes and monsoon variability. This study highlights the significance of sedimentary regime shift induced by sea-level fluctuation and monsoon dynamics in shaping OC_terr burial. It provides essential insights into the source-sink processes and paleo-environmental implications of millennial-scale sedimentary OC in tropical continental margins.