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• Sediments in the eastern Arabian Sea are mainly derived from Indus River and Deccan Plateau. • Terrestrial sources are characterized by a clear glacial-interglacial cyclical change. • Sea level controlled orbital-scale terrestrial inputs and sources in the eastern Arabian Sea. Although the uplift of the Tibetan Plateau has led to strong land-sea interactions, the characteristics of sediment transport and their controlling factors in typical marine areas in the northern Indian Ocean since the Quaternary are not clear. This work aimed to reconstruct the pattern of change in the sources of sediments since the Marine Isotope Stage 9 (MIS 9) period and to explore the mechanism of their response to changes in the marine environment in the Arabian Sea. To this end, a comprehensive multi-indicator study of the chronology and geochemical elements was carried out in core AS05-7 from the eastern Arabian Sea. Major trace element factor analysis and rare earth element (La/Yb) N -δEu N mapping suggested that sediments in the eastern Arabian Sea were mainly derived from terrestrial inputs from the Indus River and the Deccan Plateau. The sediments showed a clear glacial-interglacial cycle of change, with the contribution of the Indus River increasing during the interglacial period and that of the Deccan Plateau increasing during the glacial period. On average, the Indus River and Deccan Plateau contributed 71 % and 29 %, respectively, to the total amount of sediment. Indicators such as mass accumulation rate and Ca/Ti showed that the inputs from the terrestrial sources showed clear glacial-interglacial characteristics, with inputs during the glacial period being higher than those during the interglacial period. The lowering of the sea level during the glacial period led to an increase in the exposed area of the shelf, the shifting of deposition centers closer to the core, an increase in the rate of mass accumulation, and an increase in riverine inputs to the sea when clastic sediments from the Deccan Plateau increased. The elevation of the sea level during the interglacial period led to the inundation of the shelf, the shifting of deposition centers away from the core, a decrease in the rate of mass accumulation, and a reduction in riverine inputs to the sea when detrital sediments from the Deccan Plateau decreased. Changes in terrestrial inputs and sources revealed the orbital-scale control of sea-level change on sedimentary processes in the Arabian Sea and provided direct evidence for the "source-sink" model of sedimentation in the tropical Indian Ocean. [ABSTRACT FROM AUTHOR]

• The Irrawaddy River and Ganges-Brahmaputra rivers are the main sediment sources of the northern Ninetyeast Ridge over the last 50 kyr. • Millennial-scale periodic changes of weathering and terrigenous input are revealed during the last glacial period. • Shift of depositional center from Bengal Fan to the continental shelf is controlled by sea level changes. The Ninetyeast Ridge is situated within the world's largest sediment "source-sink" system, which extends from the Tibetan Plateau to the Bay of Bengal (BoB). Modest and stable sedimentation rate makes it a suitable region for studying long-term land-sea interaction. Recent research has primarily focused on the northern Bengal Fan, leaving limited knowledge about sedimentary processes on the distant Ninetyeast Ridge. This study aims to address this gap by investigating sediment transport pattern and its response to climatic and environmental changes since the last glacial period, using the gravity core (CJ04–50) selected from the northern Ninetyeast Ridge. The provenance discrimination based on δEu-(Gd/Yb) N revealed that the Irrawaddy (Irr) River, along with the Ganges-Brahmaputra (G-B) Rivers, represented the primary sources of the study area. Quantitative analysis equations indicated that the contribution of the G-B Rivers decreased from the last glacial period (22%) to the Holocene period (16%), while that of the Irr River increased (from 78% to 84%). Chemical index of alteration (CIA*) values, and terrigenous input proxy indicators (Ti/Ca, Rb/Sr) were used to indicate the changes of weathering and terrigenous input over the past 50 kyr. During the last glacial period, CIA*, Ti/Ca and Rb/Sr revealed significantly millennial-scale periodic changes, including the distinct declining trend during the Last Glacial Maximum (LGM) and Heinrich 2–4 (H2-H4) periods, followed by recovery trend during subsequent warm periods. During these cold periods of LGM and H2–H4, weakened Indian monsoon condition, reduced precipitation, cold climate, and expanding ice sheets, adversely affected physical erosion and chemical weathering in the source area, and the reduced river runoff impeded sediment transport. Conversely, these environmental factors reversed during relatively warm periods. Since the Holocene, CIA*, Ti/Ca and Rb/Sr declined, which was contrast to the climate change, and the sea level changes became the dominant factor. The rapidly rising sea level submerged the main terrigenous input channel (the Swatch of No Ground) of the G-B Rivers, made the depositional center shift from the Bengal Fan to the continental shelf, causing the decline of terrigenous input and lower CIA* values. [ABSTRACT FROM AUTHOR]

[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]

Lithogenic grain-size, geochemical elements of core sediments from the central Bay of Bengal (BoB) were analyzed to identify sediment provenance and explore the regional "source-sink" processes since 25 ka. Based on the geochemical compositions of core BoB-88, relative contributions of three end-member sources (Himalayan, Myanmar, Indian Peninsula) were calculated and support the general understanding that Himalayan sources were dominant since the last glacial period, which could reach 70% on average in our study. However, sediments from the Indian Peninsula and Myanmar also contributed nonnegligible materials to the central BoB since 25 ka, especially the former shows an obvious increase since 7.5 ka, which was neglected in the previous studies. To trace the sedimentary processes of different provenance terrigenous materials and reveal their response to climate changes, four typical stages with obvious provenance percent variation, including the Last Glacial Maximum period (LGM), Heinrich 1 (H1), Early Holocene Climate Optimum (EHCO), and mid-late Holocene period, were highlighted and discussed. Sea-level change played a dominant role in the glacial-interglacial scale by controlling the transition of deposition center between the shelf/subaquatic delta and the Bengal Fan, especially for sediment from the Himalayan source, exerting influence on contributions from different provenance end-members between the Holocene and the last glacial period. The opposite directions of the southwest and northeast monsoon current in the BoB have a significant influence on the transfer of the Indian Peninsula and Myanmar materials to the studied core, which led to an increase of up to 11% than the average of the Indian Peninsula and a decrease of up to 9% than the average of the Myanmar source during the Holocene. The balance between sea level (limited transport to the deep sea) and ISM (improved erosion production and output to the BoB) during the mid-late Holocene period maintained the stability of Himalayan source percent. Due to the control of the ISM variations, the Himalayan source showed a decrease of up to 20% and 21% than average during the LGM and H1 period, respectively, and an increase of up to 14% than average during the EHCO. The Myanmar source exhibited fluctuations around the average value during the LGM period, but an obvious increase of up to 21% during the H1 period and a decrease up to 8% during the EHCO, while the Indian Peninsula source percent showed little variations during the LGM and H1, but a decrease of up to 6% during the EHCO. Obvious 1/4 processional and millennial periodic changes (5.0 kyr and 1.1 kyr) of contribution proportions from three end-members provide additional evidences for the climate control on the regional source-sink processes and proved the controlled mechanisms of the orbital parameters and possible influence from the solar activity on millennial scales. [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]

[Display omitted] • Millennial-scale climate variability in the Bay of Bengal is reconstructed by TEX 86. • Warming trend during millennial-scale cold events is revealed in the northern Indian Ocean. • Atmospheric CO 2 force SST change during the millennial-scale cold events over the past 40 kyr. To better understand the process of hydrographic and temperature changes in the Indian Ocean, we present Glycerol dialkyl glycerol tetraether data on core BoB-56 from the Bay of Bengal to reconstruct the sea surface temperature (SST) variability during the last glaciation. The results indicate that the TEX 86 -derived SST ranged from 22.00 to 28.30 °C with several fluctuations since 40 ka BP and that the evolution pattern matched well with the marine isotope stage (MIS). During MIS 3, the SST kept around 24.60 °C with some small amplitudes. The SST showed more significant fluctuations during MIS 2 and increased gradually with a ~3 °C cooling during the Last Glacial Maximum (LGM). After the Younger Dryas (YD) stage, Holocene SST values exhibited miniscule variations. During the last glaciation climate variability process, the cold signals of the YD and Heinrich events were recorded well in our core SST series, revealing a regional response to global climate changes. The warming trend during these millennial-scale cold events in the northern Indian Ocean was also identified, and SST increased in the range of 2 °C. A comparison of SST records and atmospheric CO 2 concentration shows that the warming process during the YD, LGM, and Heinrich (1–4) events matched the gradual increase in atmospheric CO 2 concentration in the northern Indian Ocean. Hence, this study implies millennial-scale hydroclimate change linked with atmospheric CO 2 forcing that could improve our knowledge of the role of atmospheric CO 2 in triggering abrupt Indian Ocean climate changes. [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]

We present a sedimentary multi-index comprehensive study on sediment core BoB-56 collected from the central Bay of Bengal (BoB) with an attempt to understand the sedimentary processes and their responses to sea level change and the Indian summer monsoon (ISM) since the last glacial period. We revealed the temporal evolution of terrigenous input and provided a brief discussion of the implications of our sedimentary indexes for ocean productivity. Then, we proposed a simple depositional model in the central BoB since the last glacial period. As indicated by the geochemistry, mineralogy and physical indexes, including linear sedimentary rate (LSR), Ti/Ca, Rb/Sr and quartz/calcite ratios, the terrigenous input was higher during the last glacial period than during the Holocene period, and the sea level is suggested to be responsible for this significant distinction through the depositional center transition in the BoB at the glacial-interglacial scale. Similar terrigenous input patterns with solar radiation and precipitation before 18 ka indicated that the monsoon controlled these situations at precession-related scales. Synchronous changes with records in the north Atlantic Ocean during the last deglaciation and early Holocene suggested terrigenous input responses to the climate changes that also recorded by high latitude sedimentary system at millennial scales. Indicated by the element (CaCO 3 , Ba and Sr) authigenic accumulation rates, the paleoproductivity in the central BoB was at a roughly equivalent level during the last glacial period and the Holocene period. Different terrestrial nutrient inputs and ISM-related ocean surface stratifications were suggested to be responsible for the level of paleoproductivity. This study provides a brief understanding of the sedimentary response to the climate and emphasizes the different roles of the sea level and ISM in the central BoB. • High-resolution systematic study of the sedimentary characteristics since last glacial period; • The different roles of sea level and Indian summer monsoon in the sedimentation of the Bay of Bengal are clarified; • Sedimentary process during the last deglaciation was in response to climate change in the North Atlantic; • A simple depositional pattern in the central BoB since the last glacial period was built [ABSTRACT FROM AUTHOR]

The Bengal Fan is world famous for its developed turbiditic system. This study identified turbidite records in a gravity core (BoB-104) taken from near a currently inactive channel (E4) based on lithology, geochemical and mineralogical parameters. This core contained turbidite and hemipelagic layers in this core. This study identified 21 turbidite layers which exhibited consistent provenance with the hemipelagic layers, showing a two end-member mixing pattern and indicating consistent sources since the last glacial period. Typical turbidite layer analysis was used to study the possible turbidite deposition mechanism. Features such as the lithology break interface, normal graded sequence, a consistent pattern of a sharp increase and gradual decrease in the variation of the mean grain size (Mz), and median grain size (D50) and Si/Al ratios commonly implied a continuous deposition in accordance with variations in densities and particle sizes. This study identified long-term evolution of turbidite deposition in the eastern middle Bengal Fan that appears to be the last and indispensable part of the systematic response of the "Bengal depositional system" to the climate. Four stages were identified from the turbidite records and all the identified intervals showed synchronous changes with the entire system. The Indian summer monsoon (ISM) played a dominant role in the system interactions. The sea level affects the turbidity system by regulating the transition of the deposition center between the deep-sea and the shelf, whereas the migration of the main channel to the "Active Valley (AV)" between 14.5 ka to 10.4 ka almost halted the deposition of turbidites along the E4 channel. Thus, turbidity activity in the eastern middle Bengal Fan is not an isolated incident but part of a comprehensive system resuling from global and regional changes at different scales. • 21 turbidite layers have been identified in a core near a currently inactive channel on the eastern middle Bengal Fan. • Effective identification index system, including lithology and multiple proxies has been established and applied. • Turbidite were deposited in accordance to differences in density and particle size forming a normal graded sequence. • Long-term evolution of turbidite appears to be the last and indispensable part of the systematic response to the climate. [ABSTRACT FROM AUTHOR]

Coastal depositional systems play a crucial role in the sequestration of terrigenous organic carbon (OC), especially deltas and coastal mud belts, which are two of the most efficient OC burial hotspots. Investigation into long-term coastal OC burial is challenging since the analysis of modern coastal environments only provides a snapshot of OC burial. Marine Isotope Stage 3 (MIS 3) refers to a unique interval in the last glacial period, characterized by a protracted falling sea level punctuated by millennial-scale climate oscillations. The study of OC burial during MIS 3 can help to estimate and predict changes in coastal OC burial driven by sea-level oscillations and extreme climate events. Here, we target late MIS 3 strata beneath the southern East China Sea. Based on the analysis of total organic carbon, total nitrogen content, stable organic carbon isotopic composition, and major and trace elements, this study demonstrates that relative sea-level changes control sediment provenance and sedimentary processes in coastal environments, which in turn regulate coastal OC burial during the late MIS 3. The burial of OC in the coastal ocean during MIS 3 deviates from the typical expectation that carbon burial is facilitated during transgression or high sea-level periods. Sediments deposited during high sea-level periods in late MIS 3 exhibit the lowest OC burial flux and contents due to long-distance transport from distant sources. The study highlights that the highest burial flux and contents of OC were found in deposits preserved during sea-level lowstands. This indicates that short-distance transport, local sources, and mountainous rivers affected by the monsoon and experience frequent floods, are associated with the highest OC burial and contents. Short and rapid climate warming events likely contribute to OC burial in late MIS 3 by intensifying precipitation and nutrient-rich supplies, thereby increasing the input of terrestrial and marine OC. This observation is noteworthy as it challenges the conventional understanding of the relationship between sea level and carbon burial. The study of OC burial in late MIS 3 is helpful in understanding how OC burial reacts to sea level oscillations and rapid climate warming events. • Relative sea-level changes control organic carbon burial of the coastal system through regulating shifts in depositional environments and changes in sediment provenance. • Warming periods promote organic carbon burial in Late MIS 3 through intense precipitation and rich supplies of nutrients that increase the terrestrial and marine OC input. • Low sea-level stages are potential organic carbon sequestration periods. [ABSTRACT FROM AUTHOR]

As the biggest submarine fan in the world, the Bangal fan receives huge amounts of terrestrial materials from adjacent coastal areas, which record abundant information of environmental evolution and sedimentary system change. Based on data of Sr-Nd isotopes and clay minerals in the sediments of a gravity core BoB-56 in the central Bay of Bengal, sediment provenance and sedimentary process responding to sea level and Indian Monsoon change was studied. The results show that clay minerals and Sr-Nd isotopes compositions are obviously different during Holocene and the last glacial period. The content of smectite has increased significantly since Holocene, while illite content has decreased. The Nd isotope shows a more negative composition during Holocene than that during the last glacial period, and Sr isotope shows lower values during Holocene with a short increase at the end of Holocene. The sea level mainly controls the sedimentary pattern through the transfer of deposition centers (located in the Bengal Fan during lower sea level stand, and in the shelf and delta during the Holocene higher sea level stand), while Indian Monsoon mainly plays an important role in sediment generation, transport and circulation by controlling the production of erosion materials, precipitation, runoff and monsoon surface current. Indian summer monsoon intensity has increased significantly during Holocene, which strengthens the southwest monsoon current, thus more of the Indian Peninsula material is transported to the study area, while the contribution from Indo-Burman Ridge and Irrawaddy River material transported by the northeast monsoon current has decreased. This study was supported by the NSFC-Shandong Joint Fund for Marine Science Research Centers (U1606401) and International Cooperation Project of Global Change and Ocean-Atmosphere Interaction (GASI-GEOGE-03) [ABSTRACT FROM AUTHOR]