Last 35,000-year water column temperature and productivity variation in the Eastern Arabian Sea: monsoon and global climate connection
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A radiocarbon-dated sediment core from the flat top of Wadia Guyot at a 1500-m water depth in the Eastern Arabian Sea (EAS), western margin of India, preserves the records of past changes in water column temperatures and surface productivity. The time-series of oxygen isotope record extracted from planktonic foraminifera Globigerinoides (G.) sacculifer allows us to identify the Last Glacial Maximum (LGM, Ave. + 0.3 ‰: ~ 28–20 ka), the deglacial transition (a decrease from + 0.3‰ to − 1.2‰: ~ 20–11 ka), and the Holocene intervals (Ave. − 1.2‰: ~ 11–5 ka). The LGM cooling of the mixed layer by ~ 2 °C, thermocline by ~ 3 °C, and bottom water by ~ 4 °C is evident. The commencement of deglacial warming of the mixed layer lags thermocline warming by ~ 1 ky and bottom water warming by ~ 3ky. As different water masses of local and remote origin occur at different depths in the EAS, the observed offsets in timing and magnitude of changes in the temperatures through deglaciation indicate their independent behavior to past climate variation. The time-series of Corg, n-alkanes, and abundance of Uvigerina spp. exhibit distinct enrichments during the LGM as compared to Holocene (~ 1.7% vs 1.1%; ~ 1800 ng/g vs 1200 ng/g and ~ 20 vs < 5 tests/g of coarse fraction, respectively), which suggest enhanced surface productivity and accordingly increased export production.
The authors thank the anonymous reviewers for constructive comments and suggestions and crew and officers of the IB. Boris Petrov for assistance in sampling. The sediment core was collected during a cruise for Cobalt Crust Exploration Project funded to VKB by the Ministry of Earth Sciences. RS and VP thank the CSIR and UGC respectively for doctoral Fellowship. Mike Hall and James Rolfe of Cambridge University and De Martino Mitzi of Arizona University are thanked for measuring oxygen isotopes and radiocarbon respectively. This is NIO manuscript Ref. No: 0012-821X.
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