Climate induced changes in the circulation and dispersal patterns of the fluvial sources during late Quaternary in the middle Bengal Fan

Abstract

From a transact along 15 • N latitude in the middle Bengal Fan, temporal and spatial variations in the granulometric parameters and clay minerals in 14 C dated box cores from the eastern, the central and the western regions were studied to determine climate induced changes in the hydrography. Clay assemblages have spatial and temporal changes and are markedly different in the eastern and the western bay. From a high abundance of the clay smectite, which has its major source in the Deccan Basalt in peninsular India, it is inferred that the western bay is predominantly a depocenter of 'peninsular sources'. The eastern and the central regions of the bay, however, mostly receive sediments of the 'Himalayan source'. Related to unstable climate, the reported dominant illite-chlorite (I + C) assemblage in the eastern region of the bay (I + C > 60% smectite < 15%), between 18 and 12.6 ka BP, points to a predominant supply from the Himalayan sources through equatorwards dispersal by the winter hydrography. Higher smectite, and reduced clays of the Himalayan sources (smectite > 25%; I + C > 45%) are reported also after 12.5 ka BP from the eastern bay. These are interpreted as evidences of an intensified SW monsoon and associated change in the dispersal pattern by stronger summer monsoon hydrography which supports across bay dispersal by anticyclonic gyre. The influence of climate on hydrographic changes is consistent during the short events of arid climate (weak NE monsoon) in Holocene in core 31/1(western bay), in which the enhanced contents of the clays of the Himalayan sources are observed (smectite < 40% I + C > 50%). These findings have implications for climate regulated influence of fluvial processes over the areas, hitherto, considered unaffected by the Indian peninsular fluvial sources.

Provenance of the Late Quaternary sediments in the Andaman Sea: Implications for monsoon variability and ocean circulation

“…Mass accumulation rates calculated based on dry bulk density of samples, determined using the method of Lyle and Dymond [], vary from 5.5 to 6.3 g/cm 2 /kyr during the Holocene compared a much lower value of 1.8 g/cm 2 /kyr during the LGM. Although sedimentation/accumulation rate in deep sea is generally affected by a variety of sedimentological processes such as dynamics of transportation on land, circulation patterns in the ocean, local processes like turbidite channelized delivery, and reworking during sea level changes; in the northern Indian Ocean, it is largely controlled by variability in continental weathering and erosion linked to changes in the strength and coverage of the SW monsoon [e.g., Chauhan and Vogelsang , ]. We, therefore, believe that the major shifts observed in SK‐234‐60 could be directly linked to changes in amount of continental erosion as a function of fluctuations of the SW monsoon.…”

Indian Monsoonal Variations During the Past 80 Kyr Recorded in NGHP‐02 Hole 19B, Western Bay of Bengal: Implications From Chemical and Mineral Properties

“…Peak precipitation during the Indian summer monsoon enhances these river discharges and increases sediment transport and physical and chemical weathering in these river catchments (e.g., Chakrapani & Subramanian, 1990a, 1990bHart, 1999;Ota et al, 2017;Prasanna Kumar et al, 2007;Singh et al, 2007). Once in the bay, riverine sediments are transported by surface and intermediate currents that flow counterclockwise in the northern Bay of Bengal during the winter, when winds are northeasterly, and clockwise during the summer, when winds are southwesterly ( Figure 1; Chauhan & Vogelsang, 2006).…”

Link between Indian monsoon rainfall and physical erosion in the Himalayan system during the Holocene

“…The Indian monsoon results from a differential land‐sea sensitive heating between the northern Indian Ocean and the Asian continent (Tibetan Plateau) in response to insolation forcing and is characterized by a seasonal switch in wind direction, precipitation, and runoff [ Webster , ]. The seasonal change in the wind direction generates a reversal of surface currents in the Bay of Bengal, which shift from a cyclonic gyre during the winter monsoon to an anticyclonic gyre during the summer monsoon [e.g., Unger et al ., ; Chauhan and Vogelsang , ] (Figure ). Numerous studies have provided insights into the evolution of the Indian summer monsoon intensity over the Indian subcontinent, the Tibetan plateau, and the Himalayas through the Holocene [e.g., Gasse et al ., ; Kudrass et al ., ; Dykoski et al ., ; Berkelhammer et al ., ; Cai et al ., ; Marzin et al ., ; Contreras‐Rosales et al ., ; Sarkar et al ., ; Zorzi et al ., ].…”

“… Geographical setting and prevalent hydrography (modified from Chauhan and Vogelsang []) of the Bay of Bengal and the surrounding area. Locations of cores discussed in this manuscript are represented by the red dots.…”