Hydroclimate Variability in the Equatorial Western Indian Ocean for the Last 250,000 Years

Abstract

Indian Ocean sea surface temperatures impact precipitation across the basin through coupled ocean-atmosphere responses to changes in climate. To understand the hydroclimate response over the western Indian Ocean and equatorial east Africa to different forcing mechanisms, we present four new proxy reconstructions from core VM19-193 (2.98°N, 51.47°E) that span the last 250 ky. Sub-surface water temperatures (Sub-T; TEX86) show strong precessional (23 ky) variability that is primarily influenced by maximum incoming solar radiation (insolation) during the Northern Hemisphere spring season, likely indicating that local insolation dominates the upper water column at this tropical location over time. Leaf waxes, on the other hand, reflect two different precipitation signals: δ13Cwax (in phase with boreal fall insolation) is likely reflecting vegetation changes in response to local rainfall over east Africa, whereas δDprecip (primarily driven by boreal summer insolation) represents changes in regional circulation associated with the summer monsoon. Glacial-interglacial changes in ocean temperatures support glacial shelf exposure over the Maritime Continent in the eastern Indian Ocean and the subsequent weakening of the Indian Walker Circulation as a mechanism driving 100 ky climate variability across the tropical Indo-Pacific. Additionally, the 100 ky spectral power in δDprecip supports a basin-wide weakening of summer monsoon circulation in response to glacial climates. Overall, the proxy records from VM19-193 indicate that both precession and glacial-interglacial cycles exert control over hydroclimate at this tropical location. © 2023. American Geophysical Union. All Rights Reserved.