Changes in the upper water-column structure of the eastern equatorial Indian Ocean during 12.8 4.7 ka
Date
2025Author
Singh, P.
Singh, A.D.
Tripathi, S.
Singh, H.
Maurya, A.S.
Naik, S.S.
Kumar, R.
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The eastern equatorial Indian Ocean (EEIO), a pivotal region of the Indo-Pacific Warm Pool, plays a crucial role in modulating both the regional and global climate. Its complex hydrography is mainly influenced by an interplay of multiple ocean and atmospheric processes, i.e., inter-oceanic heat exchange (Indonesian throughflow; ITF), ocean-atmosphere interactions (Indian Ocean Dipole; IOD and El Ni o-Southern Oscillation; ENSO) and seasonal monsoon circulations, at varying time-scales. However, the associated feedbacks of these climatic components and the impact on EEIO hydrography over millennial time-scales remain unclear, thus highlighting the need for further investigation. Here, we present well-dated records of the planktic foraminiferal proxies (% Globigerina bulloides, % symbiont-barren and symbiont-bearing species) and stable oxygen isotope (?18O of Globigerinoides ruber (r) and Pulleniatina obliquiloculata (o), and ??18Or-o) at multi-centennial to millennial scale resolutions from a spade core SC-04B, retrieved from a specific location of the EEIO (8.40 S, 98.00 E). The core spans the late deglacial to middle Holocene period (12.8 4.7 ka). Using faunal and isotope proxies, we reconstructed changes in surface hydrography, productivity, and the upper water-column structure during 12.8 4.7 ka, and explored their potential links with the ITF, IOD-like mean state, and South Asian Monsoon (SAM) variability. We document the increased influence of surface ITF during 12.8 to ?9.8 ka that switched to thermocline ITF during ?9.8 to 4.7 ka. When compared with existing oceanic and land-based paleoclimate records from the Indian Ocean and adjacent continents, our faunal proxies suggest an intensification of the southeast (SE) monsoon winds and upwelling-induced surface productivity in the EEIO during the periods of 12 9.2, 8.0 7.3, 6.4 5.6, and 5.2 4.7 ka. These intervals correspond to conditions similar to a positive IOD (pIOD)-like mean state in the tropical Indian Ocean, when SAM was also intensified. In contrast, during 12.8 12, 9.2 8.0, 7.3 6.4, and 5.6 5.2 ka, weakened SE monsoon winds led to increased precipitation-induced stratification, creating surface conditions similar to a negative IOD (nIOD)-like mean state, which suppressed surface productivity in the EEIO. Further, we record four distinct intervals (?6, ?8.2, ?10.5, and ?12 ka) of low % G. bulloides abundance and corresponding low values of ??18Or-o, which appear to coincide with the cold phases in the North Atlantic [Bond Events (BEs) 4, 5, 7 and Younger Dryas (YD)]. We think that these changes were possibly linked with the intensified northwest (NW) monsoon winds and could have been modulated by the North Atlantic cold events potentially through atmospheric teleconnections.
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