Warming trend during millennial-scale cold events in the northern Indian Ocean and potential atmospheric CO2 forcing during the past 40 kyr

Abstract

To better understand the process of hydrographic and temperature changes in the Indian Ocean, we present Glycerol dialkyl glycerol tetraether data on core BoB-56 from the Bay of Bengal to reconstruct the sea surface temperature (SST) variability during the last glaciation. The results indicate that the TEX86-derived SST ranged from 22.00 to 28.30 degrees C with several fluctuations since 40 ka BP and that the evolution pattern matched well with the marine isotope stage (MIS). During MIS 3, the SST kept around 24.60 degrees C with some small amplitudes. The SST showed more significant fluctuations during MIS 2 and increased gradually with a similar to 3 degrees C cooling during the Last Glacial Maximum (LGM). After the Younger Dryas (YD) stage, Holocene SST values exhibited miniscule variations. During the last glaciation climate variability process, the cold signals of the YD and Heinrich events were recorded well in our core SST series, revealing a regional response to global climate changes. The warming trend during these millennial-scale cold events in the northern Indian Ocean was also identified, and SST increased in the range of 2 degrees C. A comparison of SST records and atmospheric CO2 concentration shows that the warming process during the YD, LGM, and Heinrich (1-4) events matched the gradual increase in atmospheric CO2 concentration in the northern Indian Ocean. Hence, this study implies millennial-scale hydroclimate change linked with atmospheric CO2 forcing that could improve our knowledge of the role of atmospheric CO2 in triggering abrupt Indian Ocean climate changes.