Depositional History and Indian Summer Monsoon Controls on the Silicate Weathering of Sediment Transported to the Eastern Arabian Sea: Geochemical Records From IODP Site U1456 Since 3.8 Ma

Abstract

Systematic variation in elemental and Sr-Nd isotopic compositions of the clay-sized (<2 μm) siliciclastic fraction from the International Ocean Discovery Program (IODP) Site U1456 (Laxmi Basin) provides valuable insights into dynamic changes in continental weathering intensity in the western Himalayas and sediment inputs from the Indus River and Deccan Traps to the eastern Arabian Sea. Long-term, high-resolution proxy records from the sediment core reveal that the main sources (i.e., Indus River and Deccan Trap basalts) of the fine-grained detrital sediments have significantly changed with Indian summer monsoon variation over the studied time interval. During two depositional periods (3.8-3.3 and 2.7-1.2 Ma) corresponding to a weak Indian summer monsoon, the Indus River contributed fine-grained sediments with high K/Al, high 87 Sr/ 86 Sr, and low εNd to the study site. Between 3.3 and 2.7 Ma and between 1.2 and 0 Ma, deposition in the eastern Arabian Sea was governed by large inputs of Deccan Trap-derived basaltic sediments, characterized by high Mg/Al and Fe/Al, low 87 Sr/ 86 Sr and chemical index of alteration values, and high εNd values, associated with a change to a stronger Indian summer monsoon driving stronger chemical weathering. Synchronous changes in the geochemical proxies since 3.8 Ma highlight that variations in the inputs of siliciclastic sediments and Indian summer monsoon development are closely coupled. Plain Language SummaryThe Indian summer monsoon is an extremely important part of the Earth's climate system. Weathering and erosion of sediments are deeply affected by monsoon rainfall. Since 3.8 Ma, the geochemical records suggest that the clay-sized siliciclastic fractions at Site U1456 were mainly derived from the Indus River when the Indian summer monsoon was generally weak. In contrast, the siliciclastic sediment supply from the Deccan Traps increased when the monsoon intensified. In particular, we propose that chemical weathering intensities can be tracked using K/Al ratios and chemical index alteration and the smectite/(illite + chlorite) in the fine fraction of marine sediments from the eastern Arabian Sea since 3.8 Ma. Conducting research in the region is of great importance for understanding past and present climatic conditions.

Climatic and Tectonic Control on the Bengal Fan Sedimentation Since the Pliocene

“…Hence, it may be inferred that monsoonal intensification during interglacials led to an enhanced contribution of sediments with more radiogenic Nd and vice versa. Variation in the εNd isotope ratios with change in the monsoonal intensity has earlier been reported from Arabian sea (Cai et al, 2019;Khim et al, 2019). An enhanced sediment contribution from the Transhimalayan Batholiths (high radiogenic Nd and less radiogenic Sr isotope ratios; Bikramaditya et al, 2020) to the Brahmaputra sediment flux is expected during monsoonal intensification (interglacial) leading to an increase in εNd values; whereas, depleted monsoon during glacial periods coupled with an orographic barrier (Anders et al, 2006;Singh & Kumar, 1997) would concentrate the erosion at the Higher Himalayan Crystalline series (Galy et al, 2010) and concomitant reduction in erosional flux from Transhimalayan Batholiths leading to decrease in εNd values (Figure 4).…”

Geochemical Records of the Provenance and Silicate Weathering/Erosion From the Eastern Arabian Sea and Their Responses to the Indian Summer Monsoon Since the Mid‐Pleistocene

“…Regarding the provenance change, α Al K and the Th/Sc ratio show similar downcore behavior since 1.2 Ma ( R = −0.59, p < 0.05), with higher amounts of Deccan Trap‐derived sediments corresponding to higher values of α Al K . Therefore, the α Al K at Site U1456 can be controlled by the leaching of mobile elements in the source regions (chemical weathering) as well as the mixing of the two sources, both of which have been suggested to be coupled with climate change (i.e., monsoon) (Cai et al, 2019). Generally, more terrigenous sediments are anticipated to be delivered from the Deccan Traps during intensified monsoon periods due to faster chemical weathering rates of Deccan volcanic rocks (21–63 t/km 2 /yr) than of other types of rocks (Dessert, 2001; O'Brien et al, 2004).…”

“…In contrast, during weakened summer monsoon periods, increased terrigenous inputs from the Indus River have been observed due to the intensification of physical erosion in the Himalayan region (e.g., Joussain et al, 2016). In this case, both strong chemical weathering and a higher contribution of the Deccan end member (more heavily weathered sediments) as a result of strong monsoon precipitation might contribute to higher α Al K values at Site U1456 (Cai et al, 2019). To some extent, the mixing of the two sources associated with monsoon intensity might enlarge the signal of α Al K induced by chemical weathering in the source regions.…”

Enhancements of Himalayan and Tibetan Erosion and the Produced Organic Carbon Burial in Distal Tropical Marginal Seas During the Quaternary Glacial Periods: An Integration of Sedimentary Records

“…New data and published results for IODP Site U1456 with different time intervals of 2.9-9.2 kyr (Cai et al, 2018(Cai et al, , 2019Chen, Xu et al, 2019Khim et al, 2018;Kim et al, 2018;Tripathi et al, 2017), together with those in 12 selected reference sediment cores with generally large fluvial discharges originating from the Himalaya and Tibetan Plateau or abundant eolian dust supplies from surrounding landmasses, continuous sedimentation, and high-resolution age model and sampling interval (An et al, 2011;Clemens et al, 1996;Fauquembergue et al, 2019;Gebregiorgis et al, 2018;Joussain et al, 2016;Lee et al, 2020;Liu et al, 2004Liu et al, , 2019Wan et al, 2017;Wang et al, 2005;Weber et al, 2018;Yu et al, 2019Yu et al, , 2020, were synthesized for the following discussion. In particular, the detailed processes related to the Himalayan highland erosion and lowland weathering, as well as their potential significance for terrestrial organic carbon transfer, delivery, and deposition in the Bay of Bengal during the Neogene over tectonic timescales and since 18 ka over millennial timescales, have been well constrained by France-Lanord and Derry (1997), Galy et al (2007), and Hein et al (2020).…”

“…In this study, we conducted the first comprehensive investigation of various proxy records for physical erosion and chemical weathering associated with the Himalaya and Tibetan Plateau using the terrestrial detritus and organic matter compositions in the distal tropical Arabian Sea, Bay of Bengal, and southern South China Sea (Figure 1). New data (Table 1) and previously published sedimentary and geochemical indicators (Tables 1-3) from 13 sediment cores in these seas (An et al, 2011;Cai et al, 2018Cai et al, , 2019Chen, Xu et al, 2019Clemens et al, 1996;Fauquembergue et al, 2019;Gebregiorgis et al, 2018;Joussain et al, 2016;Khim et al, 2018;Kim et al, 2018;Lee et al, 2020;Liu et al, 2004Liu et al, , 2019Tripathi et al, 2017;Wan et al, 2017;Wang et al, 2005;Weber et al, 2018;Yu et al, 2019Yu et al, , 2020 were integrated to establish temporal and spatial variations in the abovementioned processes, together with the associations among them. We also provide new insights into the quantitative significance of organic carbon burial in the study area for the global carbon and climate cycles during the Quaternary over orbital timescales.…”