The Late Holocene - Anthropocene Transition in the Arabian Sea: A Basin-Scale Synthesis of Monsoon-Driven Omz Expansion, Carbonate Production, and Hydrographic Stress

The Arabian Sea constitutes a key stratigraphic archive for resolving the Late Holocene–Anthropocene transition, where monsoon-driven productivity, oxygen minimum zone (OMZ) dynamics, and carbonate production record coupled natural and anthropogenic forcing within a high-resolution chronostratigraphic framework. This study integrates data from >45 sediment cores spanning ~10–40 ka, including ODP/IODP sites and regional datasets, to construct a basin-scale synthesis of multi-proxy chronologies (δ¹⁸O, δ¹³C, δ¹¹B, δ¹⁵N), radiocarbon constraints, foraminiferal assemblages, sedimentation rates, and modern CTD observations. Three domains of the Arabian Sea are identified. (1) The Oman margin is characterized by carbonate-dominated sedimentation (up to ~90–99% CaCO3), driven by upwelling-enhanced productivity and influenced by high-salinity Gulf of Oman outflow — where new CTD/core data document extreme PGW source conditions (T>34°C, S>45 psu) preconditioning northern OMZ ventilation. (2) The Pakistan margin preserves a persistent OMZ core, with elevated δ¹⁵N (6–10‰), TOC (2–8%), and laminated sediments recording intensified monsoon-driven productivity and reduced ventilation. (3) The Indian margin reflects clastic-dominated sedimentation linked to Indus discharge and comparatively weaker OMZ expression. Temporal trends indicate a mid-Holocene monsoon optimum (~7–5 ka), followed by progressive OMZ reorganization and regional decoupling of productivity and ventilation signals. Modern calibration from southeastern Arabian Gulf CTD and core surveys (2024–2025) documents extreme hydrographic conditions (T >34°C, S >42 PSU) and anti-estuarine circulation, constraining carbonate factory dynamics and seasonal proxy formation, with δ¹⁸O signals differentiating warm-season bivalve production from cooler-season coccolith sedimentation. Anthropocene stratigraphic markers, including microplastics, fly ash particles, and δ¹¹B-inferred pH decline, are superimposed on longer-term OMZ evolution. This synthesis highlights the Arabian Sea as a regionally structured yet globally significant archive linking monsoon variability, ocean deoxygenation, and carbon cycle perturbations across the Late Holocene–Anthropocene transition.