Arabian Sea stratification and deoxygenation driven by weakening monsoon winds over the Holocene

Seasonal stratification in the Arabian Sea, driven by monsoon dynamics, fuels one of the planet’s most productive marine ecosystems while intensifying oxygen minimum zones—an interplay with biogeochemical implications, yet its long-term influence on upper-ocean stratification and oxygenation remains uncertain. Here, we present century-scale sea-surface temperature reconstructions and multiproxy evidence for robust Arabian Sea warming ( ~ 1.4 ± 0.4 °C) over the Holocene. We find that stronger summer monsoon winds during the early Holocene ( ~ 10–6 thousand years ago) enhanced vertical mixing and weakened upper-ocean stratification, whereas, subsequently, monsoon weakening and surface warming strengthened upper-ocean stratification and reduced ventilation. Multiproxy indicators reveal progressive deoxygenation through the Holocene. We infer that stronger stratification reduced vertical oxygen exchange between surface and intermediate waters, while regionally variable productivity-driven oxygen demand likely amplified deoxygenation. Our findings suggest that ongoing warming may enhance stratification and favor further expansion of the Arabian Sea oxygen minimum zone. Weakening of the Indian summer monsoon and surface warming during the mid-Holocene strengthened upper ocean stratification and reduced ventilation in the Arabian Sea, according to sea-surface temperature reconstructions and multiproxy records.