Indian summer monsoon and winter hydrographic variations over past millennia resolved by clay sedimentation

Abstract

[1] Reconstruction of century-scale Indian monsoon and winter hydrography is made from an AMS-dated core located in the unique region of the southeast Arabian Sea which lies in the pathways of the lowsalinity Bay of Bengal Waters, advecting during winter northeast monsoon (NEM). Based upon clay mineral analyses in seawaters, we identify chlorite and kaolinite as specific clays supplied by the Bay of Bengal Waters and local fluvial flux (by the southwest monsoon (SWM) precipitation from the Peninsular India), respectively, along the southwest continental margin of India. An evaluation of clay flux and d18 O in G. ruber portrays century-scale weaker SWM precipitation events during ∼450-650 yr, ∼1000 yr, and 1800-2200 cal yr BP. Kaolinite wt % and flux were found to be low during all these events, though chlorite had a persistent or enhanced flux. From the enhanced flux of chlorite and reduced kaolinite/chlorite ratio, during weaker phases of SWM, we deduce a stronger NEM (winter hydrography), implying an inverse coupling between the summer and the winter monsoon.

Decreasing Indian summer monsoon on the northern Indian sub-continent during the last 180 years: evidence from five tree-ring cellulose oxygen isotope chronologies

“…Monsoon precipitation in northwestern India shows a significant decreasing trend during the period of 1866(Bhutiyani et al, 2010. However, in contrast, marine sediment records from the western and southeastern Arabian Sea exhibit an increasing trend of ISM strength over the last four centuries (Anderson et al, 2002;Chauhan et al, 2010). A recent study indicated that the contrasting trends in the ISM during the last several hundred years observed in geological records resulted from the different behavior of the Bay of Bengal branch and Arabian Sea branch of the ISM (Tan et al, 2016), and the Bay of Bengal branch of ISM weakened while intensity of Arabian Sea branch of the ISM increased during the last 200 years.…”

“…However, the tree-ring δ 18 O record in northwestern India, influenced significantly by the Arabian Sea branch of the ISM, exhibits a drying trend since 1950 CE , which does not support the idea of a strengthening Arabian Sea branch of the ISM (Anderson et al, 2002). Moreover, there are no calibrated radiocarbon dates for the (c) Shi et al, 2015a, b vs. Tierney et al, 2015a (low frequency) Wang et al, 2015a, b vs. Tierney et al, 2015a (low frequency) Cook et al, 2013a, b vs. Tierney et al, 2015a 2 1 0 -1 Shi et al, 2015a, b vs. Tierney et al, 2015a, b Wang et al, 2015a, b vs. Tierney et al, 2015a, b Cook et al, 2013a, b vs. Tierney et al, 2015a (a) last 300 years for the two records from the Arabian Sea (Anderson et al, 2002;Chauhan et al, 2010). We suggest that further high-resolution and well-dated ISM records from western India are needed to improve our understanding of the behavior of the ISM.…”

Temporal variations in 87Sr/86Sr and ɛNd in sediments of the southeastern Arabian Sea: Impact of monsoon and surface water circulation

“…However, clay mineral studies of sediments from southeastern Arabian Sea have yielded divergent conclusions; Kessarkar et al [2003] suggest that the sediments of the southeastern Arabian Sea largely represent hinterland flux and are not influenced by sediments transported from the Bay of Bengal waters during the intensification of NE monsoon. In contrast, Chauhan and Gujar [1996] and Chauhan et al [2010] argue in favor of sediment transport from Bay of Bengal during intensification of NE monsoon. [29] If sediments from the western Bay of Bengal are indeed the cause of Sr and Nd isotopic excursion, then based on a two end-member mixing model, it can be estimated that during LGM about one-fifth of sediments in SS-3101G are from western Bay of Bengal, the balance being of SS-3104G composition.…”

“…For example, investigations of surface sediments in the Arabian Sea suggest that supply from the Himalaya, Transhimalaya and Karakorum ranges brought via the Indus dominate in the northern and central regions [Garzanti et al, 2005], whereas the sediments off the shelf and slope regions of the eastern Arabian Sea are sourced mainly from peninsular India [Chauhan and Gujar, 1996;Chauhan et al, 2010;Kessarkar et al, 2003;Kolla et al, 1976;Rao and Rao, 1995]. There is also evidence based on clay mineral studies of sediments from the southwestern slope of India that suggest long range transport of Ganga-Brahmaputra sediments to the tip of Indian peninsula by surface currents [Chauhan and Gujar, 1996;Chauhan et al, 2010].…”

Impact of Indus River discharge on productivity and preservation of organic carbon in the Arabian Sea over the twentieth century

“…During a second phase, from A.D. 1700 to ca. 1900, the southwest monsoon was intensifi ed (Chauhan et al, 2010), and the freshwater input from the Indus River was high. During this phase, marine productivity was high.…”