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

Abstract

Sr and Nd isotopic composition of silicate fractions of sediments have been measured in two well dated gravity cores from the eastern Arabian Sea archiving a depositional history of ∼29 and ∼40 ka. The 87Sr/86Sr and ɛNd in the northern core (SS‐3104G; 12.8°N, 71.7°E) ranges from 0.71416 to 0.71840 and −8.8 to −12.8; these variations are limited compared to those in the southeastern core (SS‐3101G; 6.0°N, 74.0°E), in which they vary from 0.71412 to 0.72069 and −9.0 to −15.2 respectively. This suggests that the variation in the relative proportions of sediments supplied from different sources to the core SS‐3104G are limited compared to core SS‐3101G. The 87Sr/86Sr and ɛNd profiles of SS‐3101G exhibit two major excursions, ca. 9 ka and 20 ka, coinciding with periods of Holocene Intensified Monsoon Phase (IMP) and the Last Glacial Maximum (LGM) respectively with more radiogenic 87Sr/86Sr and lower ɛNd during these periods. These excursions have been explained in terms of changes in the erosion patterns in the source regions and surface circulation of the Northern Indian Ocean resulting from monsoon intensity variations. The intensification of North‐East (NE) monsoon and associated strengthening of the East Indian Coastal Current in southwest direction during LGM transported sediments with higher 87Sr/86Sr and lower ɛNd from the western Bay of Bengal to the Arabian Sea. In contrast, enhanced South‐West (SW) monsoon at ∼9 ka facilitated the transport of sediments from the northern Arabian Sea, particularly Indus derived, to the southeastern Arabian Sea. This study thus highlights the impact of monsoon variability on erosion patterns and ocean surface currents on the dispersal of sediments in determining the Sr and Nd isotopic composition of sediments deposited in the eastern Arabian Sea during the last ∼40 ka.

Lithology, Monsoon and Sea-Surface Current Control on Provenance, Dispersal and Deposition of Sediments over the Andaman Continental Shelf

“…Detrital sediments are primarily the weathered products of continental rocks with a wide range of Sr and Nd isotope ratios. The distinct isotopic compositions of these sediments can be used to track their provenance (Goldstein et al, 1984;Colin et al, 1999;Galy and France-Lanord, 2001;Singh and France-Lanord, 2002;Singh et al, 2008;Tripathy et al, 2011;Goswami et al, 2012). In the present study, the Sr and Nd isotopic composition and major elemental concentrations of silicate fractions of surface sediments of the Northern and Eastern Andaman Shelf are measured to track their provenances.…”

“…K is more abundant in feldspar and illite so that the variations in the K/Al ratio may reflect the variations in feldspar and illite abundances present in the sediments due to inherent source signature or due to weathering and transport. Higher K concentration shows more feldspar and illite (Colin et al, 1999;Singh et al, 2008) (Goldstein and O'Nions, 1981;Bouquillon et al, 1990;France-Lanord et al, 1993;Galy et al, 1996Galy et al, , 2010Winter et al, 1997;Pierson-Wickmann et al, 2001;Clift et al, 2002;Singh and France-Lanord, 2002;Banner, 2004;Ahmad et al, 2005Ahmad et al, , 2009Colin et al, 2006;Singh et al, 2008;Viers et al, 2008;Rahaman et al, 2011;Tripathy et al, 2011;Goswami et al, 2012;Awasthi et al, 2014;Ali et al, 2015). These isotope pairs are used as reliable proxies to track the sediment sources, as there are distinct differences in their composition in the different lithologies supplying these sediments.…”

“…The accuracy of these measurements was ascertained by analyzing NIST standard SDO-1 and SCo-1 along with samples. Sr-Nd isotopic analyses in the silicate fractions were carried out following established analytical methodology at Physical Research Laboratory, Ahmedabad, India (Singh et al, 2008;Goswami et al, 2012). The silicate fraction of the samples, together with known amount of 84 Sr spike was digested completely using HF−HNO 3 −HCl acids.…”

“…Pure fractions of Sr and Nd were separated from the solution using conventional column chromatography (Singh et al, 2008). Measurements of Sr and Nd isotopes were carried out using Thermo Neptune MC-ICP-MS in static multi collection mode (Goswami et al, 2012). The isotope data were corrected for instrumental mass fractionation by normalizing the Sr and Nd isotopic data with 86 Sr/ 88 Sr (=0.1194) and 146 Nd/ 144 Nd (=0.7219) respectively.…”

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“…The utility of Sr and εNd proxies for monitoring the weathering signal from rivers in the Bay of Bengal, the Arabian Sea, and other locations has been well documented (e.g., Burton and Vance, 2000;Clift and Plumb, 2008;Colin et al, 1999;Goswami et al, 2012;Osborne et al, 2008;Padmakumari et al, 2006;Rahaman et al, 2009;Stoll et al, 2007;Tripathy et al, 2011). The Nd isotope composition of the carbonate component of Bay of Bengal sediments has been used to investigate variations in the relative contribution of discharge from the Ganga-Brahmaputra, Irrawaddy, and Arakan Rivers (Burton and Vance, 2000;Gourlan et al, 2008Gourlan et al, , 2010Stoll et al, 2007).…”