Sea surface condition in the Bay of Bengal since the early Pliocene

Abstract

Modern CO2 concentrations have reached 410 ppm, and there is considerable uncertainty about how climate change will affect the variability and intensity of the Asian Monsoon System (AMS). We can improve our understanding by studying how the Indian Ocean and the AMS responded to past climate change. Although the early Pliocene is not a perfect analogue for future warming, it is the most recent time in earth history when CO2 concentrations were higher than today, and global average temperature was 3-4°C warmer. SST in the Atlantic Pacific Ocean were 3-7°C higher in the eastern basins and remained stable in the Indo-Pacific warm pool. There is little data from the Indian Ocean through the last 6 Ma, limiting our understanding of how the monsoon and ocean circulation have changed. We generated foraminifera paleoclimate records from IODP Site U1451 (8°N, 88°E in 3607m water depth) in the Bay of Bengal. The top 200 m of Site U1451 is mostly calcareous clay, and a preliminary age model indicates this interval represents the last 6 Ma. We picked ~30 T. sacculifer with samples spaced at 40 cm. Mg/Ca of T. sacculifer was measured and converted to SST using multiple published calibrations. SST using the Dekens et al., 2002, carbonate dissolution corrected calibration at Site U1451 ranges from 26-30°C, well within the range to support the atmospheric convection required to support the AMS. There appears to be no long-term cooling trend through the past ~3 Ma. This new Bay of Bengal record is similar to those from ODP Site 758 in the Indian Ocean and ODP Site 806 in the western Pacific warm pool, which record a similar SST range and long-term features in SSTs in the past ~3 Ma.