South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea

Abstract

The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial-interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay-size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval eNd values changed little, generally oscillating between 27.3 and 25.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo-Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite 1 chlorite) ratios (up to 14), as well as low 87 Sr/ 86 Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite-poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short-term northern Atlantic climate variability on millennial time scales.

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

“…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.…”

Responses of the East Asian Summer Monsoon in the Low‐Latitude South China Sea to High‐Latitude Millennial‐Scale Climatic Changes During the Last Glaciation: Evidence From a High‐Resolution Clay Mineralogical Record

“…Recently, clay mineralogical records have been demonstrated well displaying the H1 stadial occurred at around 16 ka BP in several northern SCS sediment cores Huang et al, 2011), implying that clay minerals could be used potentially as an efficient proxy to reflect the millennial-scale climate changes in the East Asian marginal seas. This mineralogical proxy has been realized by high-resolution paleoenvironmental studies in the Cariaco Basin, the Andaman Sea, and the Mediterranean Sea, indicating that clay mineralogy is sensitive enough to respond to interannual-to millennial-scale paleoenvironmental changes, such as interannual paleostorm activity, decadal lunar nodal tidal periodicity (16.8 yr), and millennial Intertropical Convergence Zone (ITCZ) shifts and monsoon variations (Ali et al, 2015;Black et al, 2009;Riboulleau et al, 2014;Sabatier et al, 2010).…”

Clay minerals of surface sediments from the lower Bengal Fan: Implications for provenance identification and transport processes

“…The average compositions of clay mineral of river sediment around the Bay of Bengal (BoB). (Godavari–Krishna data is from Bejugam & Nayak, , the samples are modern sediments at Godavari and Krishna River mouth regions; Irrawaddy data is from Colin et al, ; Rodolfo, , samples are surface sediments at Irrawaddy River Delta and cores from the adjacent ocean, Ganges–Brahmaputra data is from Datta & Subramanian, ; Hafijur et al, , samples are modern river sediments near the estuary, Andaman‐Nicobar Ridge data is from Ali et al, , samples are core sediments from the adjacent ocean) [Color figure can be viewed at wileyonlinelibrary.com]…”

“… Source: Godavari–Krishna data is from Bejugam and Nayak (); Irrawaddy data is from Rodolfo () and Colin et al (); Ganges–Brahmaputra data is from Datta and Subramanian () and Hafijur et al (); Andaman‐Nicobar Ridge data is from Ali et al ().…”