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Journal of Tropical Oceanography

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Evidence of micro-charcoal deposited in the lower fan of the Bay of Bengal reveals that the climate was arid in the early HS1

LUO Chuanxiu1, LIN Gang2, THILAKANAYAKA Adikari Mudiyanselage Vidusanka1, WEI Haicheng3, XIANG Rong1, YANG Yiping1*, WAN Sui1, LIANG Shiqing1, SU Xiang1, DU Shuhuan1, ZHANG Lanlan1, LIU Jianguo1, HUANG Yun1, SOE Moe Lwin 4#br# #br#   

  1. 1. State Key Laboratory of Tropical Marine Environment and Island and Reef Ecology (South China Sea Institute of Oceanography, Chinese Academy of Sciences), Guangzhou, Guangdong 510301, China;
    2. South China Sea Ecological Center, Ministry of Natural Resources, Nansha Coral Reef Ecosystem Field Scientific Observation and Research Station, Key Laboratory of Marine Environment Detection Technology and Application, Ministry of Natural Resources, Guangzhou, Guangzhou, 510301, China;
    3. Key Laboratory of Salt Lake Geology and Environment of Qinghai Province (Qinghai Institute of Salt Lakes, Chinese Academy of Sciences), Xining, Qinghai 810008, China;

    4.Department of Geology, Dagon University, Yangon 11422, Myanmar

  • Received:2025-06-27 Revised:2025-08-15 Accepted:2025-09-30
  • Supported by:

    The Science and Technology Plan Project of Qinghai Province Incentive Fund 2024；the National Natural Science Foundation of China (42376074)

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Abstract: Previous studies have suggested that the mean position of the tropical convergence zone (ITCZ) rain-belt shifted southward due to the cooling of the Northern Hemisphere during the Heinrich Stadial I (HS1) period (approximately 16.3 - 18.3 ka B.P.). However, an alternative perspective proposes that tropical precipitation in the Indo-Asian-Australian (IAA) monsoon region may have undergone a meridional contraction during the early HS1. It can be seen that the response and displacement amplitude of the ITCZ to the cooling event in the North Atlantic during HS1 remain controversial. Marine charcoal records from the Bay of Bengal may preserve critical information about climate-driven ancient fire events from the northern land. In this study, we find that the total concentration of charcoal and the percentage of woody charcoal in YDY09 core (located at 9.9°N) declined to the lowest levels in the Early HS1, while the percentage of herbaceous charcoal increased. This suggests a sharp reduction in the frequency of fire events, consistent with decreased rainfall inferred from the δ18O records of foraminifera and stalagmites, and other proxies. The decline in fire events may be related to reduced vegetation cover under drier climate and cooler climatic conditions，reflecting that the source area was outside the range of the ITCZ at that time. The change aligns with evidence of aridity from low pollen values of evergreen broad-leaved forest in YDY10 core (located at 9.9°N) and E87-32B core from the upper submarine fan of the Bay of Bengal. These findings support the coherence of Indian summer monsoon precipitation reconstructions using charcoal and other proxies. At the same time, the abrupt decline in fire activity in core YDY09 during the Holocene mid-period, especially the increase in herbaceous charcoal, corresponds to a sharp increase in the percentage of coprophilous fungal spore after 4.5 ka. The latter has been attributed to prehistoric human animal domestication on the southern Qinghai-Tibet Plateau, the Gangetic Plain, and eastern India. It implies that intensified grazing may have reduced herbaceous biomass, indirectly suppressing the fire intensity in this region.

Key words: Heinrich, Micro-Charcoal, Coprophilous fungal spore, the Bay of Bengal