Evidence of micro-charcoal deposited in the lower fan of the Bay of Bengal reveals an arid climate during the early Heirich Stadial 1

Previous studies have suggested that the mean position of the intertropical convergence zone (ITCZ) rain belt shifted southward due to the cooling of the Northern Hemisphere during the Heinrich Stadial 1 (HS1) early period (approximately 18.3-16.3 cal ka BP). However, recent studies indicate that wet conditions prevailed in the low-latitude region (3°N-9°N) of the Northern Hemisphere during the early HS1 period, while adjacent regions to the north and south were arid. It can be seen that the response and displacement amplitude of the ITCZ to the cooling event in the North Atlantic during early HS1 remain controversial. Marine charcoal records from the Bay of Bengal may preserve critical information about climate-driven palaeo-fire events from the surrounding land. In this study, we observe that the total concentration of charcoal and the percentage of woody charcoal in core YDY09 (located at 9°54′N) decreased to their lowest levels in early HS1, while the percentage of herbaceous charcoal increased. This suggests a sharp reduction in the strength of fire events, consistent with decreased rainfall inferred from the δ18O records of foraminifera and stalagmites and other proxies. The decline in fire strength may be related to reduced vegetation cover under drier climate and cooler climatic conditions, which aligns with evidence of aridity from low pollen values of evergreen broad-leaved forests in core YDY10 (located at 10°N) and core E87-32B (located at 15ºN) from the Bay of Bengal. During the same period, the charcoal and pollen contents in two cores on Sumatra Island (located at 6°N and 6°S, respectively) also showed humid and arid conditions, indicating that the charcoal and pollen source areas were inside and outside the ITCZ rain belt at that time. Reconstructed results of Indian Summer Monsoon precipitation based on micro-charcoal, pollen, foraminifera, and other indicators are consistent. For the first time, combined charcoal and pollen records reveal the evidence of drought outside the range of 10°N to 6°S in the early stage of HS1, while moist evidence from the 6°N core on Sumatra Island indirectly supports the inference that the ITCZ centered around 6° N during this period.