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• 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]

The long-term evolution of deep-sea turbidity current activity is closely related to climate and sea level changes; however, the impact of abrupt climate change (e.g. millennial-scale events in high northern latitudes) is poorly known. In this paper, deep-sea turbidite records in the western part of the lower Bengal Fan were identified since the Last Glacial Maximum (LGM) to investigate the effects of abrupt climate change on the development of the Earth's largest deep-sea fan. Our records show a termination of turbidite activity in the western lower fan at 16.6 ka–15.4 ka almost contemporaneous with Heinrich 1 event (a cooling stadial in high northern latitudes). The trigger of this termination in turbidite activity may have been a sharp decrease in erosion rates during a time of relatively stable sea level and rapid source-sink processes. The subsequent episodes of the Bolling/Allerod warm interstadial and Younger Dryas cold stadial and the rapid sea level rise event that followed possibly induced adjustment of turbidity current activities in the Bengal Fan, as indicated by other published records. In summary, we show that close links exist between abrupt climate changes in the high-latitude Northern Hemisphere and deep-sea turbidity current activity in the low-latitude South Asia. • Deep-sea turbidite records in the Bengal Fan since LGM were recovered. • Termination of turbidite in the western lower fan was triggered by HS1 event. • Links between high latitudes climate and low latitudes sedimentation were revealed. [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]

Submarine fan sediments are essential archives for understanding the interaction between continental weathering and climate change, but decoding multiple geological and environmental factors in such highly dynamic sedimentary environments is challenging. Here we present a high-resolution magnetic mineral record spanning the past ∼40 ka from the central Bengal Fan. Comprehensive rock magnetic and electron microscopic analyses are conducted to understand the origins of different magnetic mineral components in response to sedimentary and paleoclimate processes. Detrital magnetite and titanomagnetite are the dominant magnetic minerals in Bengal Fan sediments, whose abundance and grain size are primarily controlled by eustatic sea-level change. Increased Himalaya terrestrial input during Heinrich events is documented during sea-level low stand, but magnetic mineral variations and climate events are decoupled due to enhanced Indian hemipelagic sediment input since the last deglaciation sea-level rise. In addition, we identify an enriched biogenic magnetite layer near the Fe-redox boundary in the studied Bengal Fan sediment core, possibly related to relatively mild post-depositional diagenesis. Massive detrital inputs in the submarine fan sediments dilute the contribution of biogenic magnetite to the bulk magnetic record. Our results contribute to an integrated source-to-sink understanding of magnetic mineral components in continental margin submarine fans, which helps to construct multi-proxy Quaternary paleoclimate and paleogeography records in typical submarine fan deposits. • Direct recognition of detrital/biogenic magnetic minerals in Bengal Fan sediments. • Sea-level controls variations of detrital magnetic mineral component. • Stadial terrestrial input was enhanced during sea-level low stand. • Increased hemipelagic sediments at sea-level high stand reduce climate sensitivity. • Thriving biogenic magnetite near diagenetic Fe-redox boundary. [ABSTRACT FROM AUTHOR]