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[Display omitted] • Sediments in the southern Bay of Bengal mainly sourced from terrestrial materials transported by inflow rivers. • Multiple rivers dominated the glacial sediment provenance, whereas Indian peninsula materials increased during the Holocene. • Chemical weathering on glacial-interglacial scales was controlled by solar insolation. • Millennial variations of chemical weathering matched well with the Indian monsoon system. Chemical weathering has a significant role in controlling sediments production and transport, both of which are closely linked to environmental conditions and climate change. This study examines BoB-79, a core located in the southern part of the Bay of Bengal (BoB), to investigate the chemical weathering of terrestrial materials since the last glacial period in the Indian Ocean. Multiple geochemical proxies were employed to reconstruct the weathering history and to establish links with global and local environmental shifts. Analysis of rare earth element (REE) indices pinpointed terrestrial materials as the main sediments provenance in the southern BoB. During the last glacial stage, the sediments in core BoB-79 were sourced from multiple rivers surrounding the BoB; these deltaic systems prograded, leading to a mixture of sediments being transported to the southern BoB. Conversely, during the Holocene stage, the sedimentary signature from core BoB-79 more closely resembled that of the Krishna-Godavari rivers, indicating an increased terrestrial supply from the Indian Peninsula. Collectively, TiO 2 , the chemical index of alteration (CIA), αAlNa, and the illite chemical index were observed to align with changes in solar radiation intensity in the northern hemisphere. Millennium-scale fluctuations might be attributed to global climate events such as Heinrich 1 (H1), Younger Dryas (YD), and Bølling/Allerød (B/A) through the Indian monsoon system. Thus, investigation into the chemical weathering process and its reaction to changes of solar insolation and the Indian monsoon provide compelling evidence for understanding air-sea interactions in the southern BoB since the last glaciation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Systematic combination and comparation of bedload and suspended load of river sediment. • Effective separation of provenance, weathering and deposition signals in river sediment. • Testing the application of extracted river sediment provenance signals to marine sediment. River sediments compositions in Bangladesh were measured to extract effective signals of chemical weathering, sedimentary processes and provenances and applied to sedimentary record in the Bay of Bengal (BoB). Weathering indexes including the chemical index of alteration (CIA), weathering index of Parker (WIP), αAlE and related diagrams indicated overall weak to intermediate chemical weathering intensity in modern Ganges-Brahmaputra-Meghna (G-B-M) catchment. Sedimentary processes controlled sediment mineralogical and chemical composition to a certain extent, as reflected in the distinctions between suspended loads and bedloads. The suspended loads were richer in phyllosilicates than the bedloads in the Brahmaputra and the Meghna River sediments, and the Meghna River bedload exhibited sedimentary recycling and quartz dilution features. The Ganges River sediments showed multiple recycling and source mixing features. Extracted provenance proxies indicated that the Brahmaputra River sediments got relatively more effects from Himalayan mafic to intermediate rocks, while the Ganges River sediments indicate a mixture from the Himalaya and Indian Peninsula. more effects from ultramafic rocks were revealed for the Meghna River sediments. By comparing the extracted provenance proxies of different rivers and applying them to the identification of sediment sources in the Bay of Bengal (BoB), the Brahmaputra River is suggested to have been the primary supplier of sediments to the central-northern BoB since the last glacial period as a result of the highest erosion rate in the eastern syntaxis, which provides a new understanding of the sediment "source-sink" process in the BoB and indicates that effective extraction of fluvial information is crucial for marine sedimentology studies. [ABSTRACT FROM AUTHOR]

Changes of marine paleoproductivity could reflect the history of marine biogenic cycle process, and exploring the evolution and mechanism of marine productivity are important for understanding the global biogenic factor cycle and its roles in past, present and future climate change. Based on the analysis of biogenic silica (BSi) in core ADM-159 and core BoB-56 from the northeastern Indian Ocean, high-resolution curves of paleoproductivity evolution were obtained. The results show that the BSi contents in these two core sediments are less than 1.8%, mainly affected by the low supply of silica skeleton and the high dissolution and dilution of terrigenous materials. Distinct fluctuations in BSi contents could still be reflected, and their relative values were controlled by chemical weathering processes and terrigenous material supply. The power spectrum analysis of BSi content shows reliable periodicities of 5.86 kyr, 1.95 kyr, 1.35 kyr and 1.09 kyr, suggesting that millennial-scale BSi value might be affected by solar activity. Based on the BSi mass accumulation rates (MAR), lower paleoproductivity during the glacial period and higher level during the Holocene were revealed in our records, which matched well with the global climate changes. Temperatures controlled by low latitude insolation changes could influence the nutrient substance supply, further promote productivity variations at the glacial–interglacial scale. Some millennial events, such as the Heinrich stadial 1 (HS1) and Younger Dryas (YD) periods, showed relatively low paleoproductivity, while the Bølling/Allerød (B/A) period and the middle Holocene showed higher paleoproductivity. These millennial paleoproductivity fluctuations may be due to the changes of nutrient supply caused by Indian summer monsoon (ISM). In addition, the BSi MAR of core ADM-159 and core BoB-56 are well correlated with the isotopic compositions of Greenland ice core and Chinese speleothem, providing robust evidence for the link between northeastern Indian Ocean paleoproductivity and global climate change. • paleoproductivity variability since LGM was reconstructed by BSi in the northeastern Indian Ocean. • BSi content were controlled by supply of silica skeleton, dissolution and dilution of terrigenous materials. • Indian summer monsoon have been proved linked with tropic Indian Ocean paleoproductivity. [ABSTRACT FROM AUTHOR]

Downcore geochemical composition of sediment core retrieved from the central Andaman Sea were measured to help understanding the potential connection between chemical weathering and monsoon climate since the last glacial period. The age model was confirmed based on twelve accelerator mass spectrometry (AMS) 14C dates on planktonic foraminifera Neogloboquedrina dutertrei. Provenance discrimination results distinguished by Rare Earth Elements pattern and Sc/Th-(La/Yb) UCC diagram revealed that terrestrial sediment from the Irrawaddy River are the dominant input in the central Andaman Sea. Chemical weathering indexes, including chemical index of alteration (CIA), weathering index of Parker (WIP), αAlNa, and a stack of these data were reported and the terrestrial input was assessed using Ti/Ca ratios. These indexes showed general synchronicity with the regional monsoon precipitation and temperature record, the chemical weathering intensity and monsoon precipitation/temperature were stronger/higher during MIS 3 and MIS 1 and weaker/lower during MIS 2, indicating existence of a general "climate-driving weathering" pattern on glacial-interglacial time scales. However, certain anomalies occurred during 18–13 cal. kyr BP and 6–3 cal. kyr BP, when the chemical weathering intensity showed higher and lower values, respectively. The chemical weathering intensity enhanced during 18–14 cal. kyr BP, due to increased isolation and markedly increased temperatures, as well as lower erosion production and sediment transfer rate caused by lower precipitation, whereas the opposite conditions prevailed during 14–13 cal. kyr BP. Indeed, for the weak chemical weathering intensity during 6–3 cal. kyr BP, decreased isolation, relatively high terrestrial sediment supply, slightly lower precipitation and markedly lower temperatures were suggested to be the primary reasons, indicating the presence of a "climate-driving weathering" pattern on millennial time scales. Our findings support the hypothesis that the chemical weathering evolution in the north-eastern Indian Ocean was synchronous with both global and regional climate conditions, representing distinct changes controlled by Indian summer monsoon on different time scales. • CIA, WIP, αAlNa and Ti/Ca for chemical weathering intensity reconstruction • A "precipitation-induced weathering" mode exists on glacial-interglacial time scales. • A "temperature and terrestrial input controlled" mode on millennial time scales [ABSTRACT FROM AUTHOR]

Abstract Major and trace elements of sediments from two gravity cores (10YDY09 and 12I712) in the northeastern Indian Ocean have been analyzed for sediment provenance and the relationship of the sediments with climate change since 50 ka. The rare earth element (REE) compositions were analyzed, and the sediment contributions were estimated for the major potential sources, including the Ganges-Brahmaputra (G-B), Godavari-Krishna (G-K) and Mahanadi Rivers. Our results showed that the sediments in the study area were a mixture of sediments discharged from the above three rivers. The sediment contribution of the G-K Rivers increased notably during the Holocene when the rainfall increased, which may be caused by the strengthening of the East Indian Coastal Current (EICC) and the resulting large amounts of sediments supplied by the G-K Rivers. The higher sediment contribution from the G-B Rivers demonstrated the role of the Active Channel in transporting sediments to the distal Bengal Fan. During the last glacial maximum (LGM), especially in the late period, the Indian summer monsoon weakened, but the winter monsoon strengthened, resulting in a decrease in chemical weathering and elemental enrichment in the northeastern Indian Ocean. Conversely, when the rainfall was low, the chemical weathering strengthened and K 2 O/TiO 2 ratios were lowered due to the longer weathering time and resulting sediment potassium loss. However, when the sea level reached a certain height during the Holocene, the fluvial sediments could not easily enter deep-water environments through submarine channels, which were well developed in the Bengal Fan. Highlights • The major and trace elements of two cores were analyzed for sediment provenance. • The role of the Active Channel in the formation of the Bengal Fan was discussed. • The influence of the sea level fluctuations and rainfall changes over the past 50 ka was evaluated. • Coastal currents driven by the monsoon winds are key forces in sediment transport. [ABSTRACT FROM AUTHOR]

Based on clay mineralogy, siliciclastic grain sizes and geochemical records from deep-sea sediments in the central Bay of Bengal (BoB), the evolutionary history of the Indian summer monsoon and associated weathering process in the Himalayan system since 37 ka were reconstructed. Clay minerals and Th La elements indicate a mixture of sediments originating from the Ganges-Brahmaputra (G-B) Rivers, Indo-Burman ranges/Irrawaddy River and Godavari-Krishna (G-K) Rivers. The Th La quantitative reconstruction revealed that sediment supply from the G-B Rivers was reduced during a series of millennial-scale cold climate events (i.e., Younger Dryas and Heinrich Events) and the Last Glacial Maximum. By removing the control of sea-level factors on the percentage of clay minerals in the sediments, we suggests that the marked decrease in the illite chemistry index and the increase in the (illite+chlorite)/smectite ratio during cold climate periods reflect enhanced physical weathering and weakened chemical weathering in the Himalayan system. Comparing the contribution from the G-B Rivers and the sedimentation rates in different regions of the BoB, it was inferred that the sediments of the G-B Rivers were mostly deposited in the upper and middle Bengal Fan. During the Holocene, the Active Channel played a crucial role in delivering sediments from the G-B Rivers to the lower Bengal Fan. The decreased chemical index of alteration (CIA) and increased K₂O/TiO₂ ratio indicated the weakening of the Indian summer monsoon. At that moment, the Himalayan system was involved in cold climatic conditions accompanied by glacial extension, which led to enhanced physical weathering and increased sediment contributions from the highlands. • Core sediments are originated from the G-B Rivers, Indo-Burman ranges/Irrawaddy River and G-K Rivers. • Sediment supply from the G-B Rivers was reduced during a series of millennial-scale cold climate events. • During cold climate periods, physical weathering enhanced and chemical weathering weakened in the Himalayan system. • Sediment of G-B Rivers was mainly stored in the upper and middle BoB over the past 37 ka. • The Active Channel played a crucial role in Holocene delivering sediment from the G-B Rivers to the lower Bengal Fan. [ABSTRACT FROM AUTHOR]

[Display omitted] • Both rivers received 210Pb concentration through the physical and chemical weathering. • Rivers are a main contributor of 210Pb into offshore sediment at the east coast Peninsular Malaysia. • Atmospheric deposition and transboundary mobilization may increase the total flux of 210Pb at offshore sediments. A total of 97 surficial sediment samples were collected from the Kelantan River, Pahang River and offshore water of Peninsular Malaysia located in the east coast mainly in to investigate the sources and sinks of 210Pb in the southern South China Sea region. At the locations studied, the concentration activity of 210Pb was recorded from the Kelantan River (n = 28), Pahang River (n = 44) and offshore waters (n = 25), ranging from 2.7 ± 0.46 Bq/kg to 52.07 ± 5.23 Bq/kg, 8.65 ± 3.56 Bq/kg to 83.04 ± 6.71 Bq/kg, and 6.72 ± 2.92 Bq/kg to 42.2 ± 3.94 Bq/kg, respectively. Both riverine systems received huge amounts of 210Pb concentrations via mobilised particulate matter, where erosional igneous rocks and weathered sedimentary layers were prominent in elevating the amount of 210Pb from the source towards the sinks. In the offshore margins, the concentrations differed according to the source. As both rivers move towards the sinks in the coastal territories, boundary scavenging becomes prominent. In the offshore territories, a deficiency of 210Pb leads to excess 226Ra in the water column. Scavenged nuclide imported from several sources may increase the total concentrations lingering in the offshore waters of Peninsular Malaysia. Particulate matter mobilised from several sources via upwelling or downwelling in the bottom current through lateral transport further enhances the removal of particle-reactive nuclides from the water column. At the same time, atmospheric deposition via precipitation and transboundary mobilisation of aerosol by mineral dust may increase the total flux on the offshore waters of Peninsular Malaysia. [ABSTRACT FROM AUTHOR]