412 / 2024-09-16 15:13:32

The role of active channel on sediment transport to the Bengal Fan and Its Implications in Climate and Sediment Source Change during the last Deglaciation

Sedimentary dynamics; Geochemical elements; Climatic influence; Sediment provenance; Holocene; Sediment transport processes

The Bay of Bengal (BoB) is crucial for understanding sediment dynamics and weathering history. Analyses of four sediment cores from the western BoB, focusing on the Middle and Lower Bengal Fan (BF), reveal rapid deposition within the submarine canyon, driven by the Ganges-Brahmaputra rivers during lower sea levels, generating turbidity currents. Glacial activity during cold phases increases physical weathering in the Himalayan highlands, affecting sediment transport to the BoB before the early Holocene. However, sediment contributions from Indian subcontinental sources began after 9.5ka, reaching dominance since 7ka, transitioning from Himalayan to Indian subcontinental sources, particularly in arid-semiarid conditions in the middle to lower western BF off the channels, driven by water currents during winter monsoon. Cores near active channels maintain consistent sourcing patterns influenced by regional factors like river systems and active channels. Fluctuations in smectite/(illite+chlorite) ratios correlate with changes in summer monsoon rainfall, impacting erosion and sediment dynamics. Chemical weathering indicators reveal shifts in terrestrial material presence and weathering conditions, intensifying during the early Holocene under warmer conditions and increased rainfall. Elevated smectite/(illite+chlorite) and K/Si ratios during 9.5-6.5 ka predominantly originated from the Himalayas and/or Deccan Trap basalts. Climatic factors, particularly temperature and precipitation, drive chemical weathering processes. The warming trend during the Holocene has strengthened the summer southwestern monsoon, a significant weathering driver in the Himalayan region. Active channels crucially transport sediments primarily from the Himalayas sources to the deeper fan. However, their roles in sediment transport have declined post-sea level rise, primarily influenced by monsoonal currents. Particularly during the HCO period, the intensification of the summer monsoon led to increased sediment contributions from Indian sources, driven by water currents during the winter monsoon, with notable impacts after the mid-Holocene.