Indian summer monsoon forcing on the deglacial polar cold reversals

Abstract

The deglacial transition from the last glacial maximum at ∼20 kiloyears before present (ka) to the Holocene (11.7 ka to Present) was interrupted by millennial-scale cold reversals, viz., Antarctic Cold Reversal (∼14.5-12.8 ka) and Greenland Younger Dryas (∼12.8-11.8 ka) which had different timings and extent of cooling in each hemisphere. The cause of this synchronously initiated, but different hemispheric cooling during these cold reversals (Antarctic Cold Reversal ∼3 • C and Younger Dryas ∼10 • C) is elusive because CO 2 , the fundamental forcing for deglaciation, and Atlantic meridional overturning circulation, the driver of antiphased bipolar climate response, both fail to explain this asymmetry. We use centennialresolution records of the local surface water δ 18 O of the Eastern Arabian Sea, which constitutes a proxy for the precipitation associated with the Indian Summer Monsoon, and other tropical precipitation records to deduce the role of tropical forcing in the polar cold reversals. We hypothesize a mechanism for tropical forcing, via the Indian Summer Monsoons, of the polar cold reversals by migration of the Inter-Tropical Convergence Zone and the associated cross-equatorial heat transport.

Last 42 Ky Sediment Chemistry of Oxygen Deficient Coastal Region of the Bay of Bengal: Implications for Terrigenous Input and Monsoon Variability

“…The holocene/marine oxygen 4). Such D-O type of climate variability is also reported in cave deposits of Meghalaya 18 and other sedimentary records from the eastern margin of India 13 and from Arabian Sea [19][20][21] , which formed the basis for reconstructing ISM variability. Hence, the present  18 O G.sacculifer timeseries can be interpreted in terms of ISM intensity.…”

“…The dramatic shifts in  18 O G.sacculifer from 0.2‰ down to 2.2‰ at the BA and from 2.2‰ up to 0.0‰ at the YD suggest extreme intensification followed by rapid weakening of the ISM. Thus, ISM appears to have been remarkably unstable during the deglacial transition [19][20][21][22][23] . A moderate enrichment of  18 O G.sacculifer is evident at 5-6 ka (Figure 4) suggesting mid-Holocene weakening of ISM.…”

Glacial events during the last glacial termination in the Pagele valley, Qiongmu Gangri peak, southern Tibetan Plateau, and their links to oceanic and atmospheric circulation

“…The warmer and wetter conditions of the GI-1 period can be attributed to the enhanced THC, with the ITCZ shifting northward and thus the Indian summer monsoon being strengthened (Sinha et al, 2005; Liu et al, 2009; Banakar et al, 2017). Despite the relatively warmer conditions in the GI-1 period, it still appeared to be colder relative to the GS-1 period in the Qiongmu Gangri peak region, as evidenced by our glacier–climate modeling on the basis of the greater glacial extent of PM2 than PM3.…”