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Among various climate drivers, direct evidence for the Intertropical Convergence Zone (ITCZ) control of sediment supply on the millennial scale is lacking, and the changes in ITCZ migration demonstrated in paleoclimate records need to be better investigated. Here, we use clay minerals and Sr–Nd isotopes obtained from a gravity core on the Ninetyeast Ridge to track the corresponding source variations and analyze the relationship between terrestrial material supply and climatic changes. On the glacial–interglacial scale, chemical weathering weakened during the North Atlantic cold-climate periods and falling sea level hindered the transport of smectite into the study area due to the exposure of Andaman and Nicobar Islands. However, the influence of the South Asian monsoon on the sediment supply was not obvious on the millennial scale. We suggest that the north–south migration of the ITCZ controlled the rainfall in Myanmar and further directly determined the supply of clay minerals on the millennium scale because the transport of smectite was highly connected with the ITCZ location; thus, the regional shift of the ITCZ induced an abnormal increase in the smectite percentage during the late Last Glacial Maximum (LGM) in our records. The smectite percentage in the studied core is similar to distinct ITCZ records but different in some periods, revealing that regional changes in the ITCZ were significantly obvious, the ITCZ is not a simple north–south displacement, and closer connections occurred between the Northern–Southern Hemisphere in the eastern Indian Ocean during the late LGM. [ABSTRACT FROM AUTHOR]

• Clay minerals are mainly derived from terrestrial sources input from the Irrawaddy River. • Solar activity controlled the weathering and sedimentation of fine-grained sediments. • Monsoon precipitation controlled the millennial supply and transport of fine-grained sediments. The uplift of the Tibetan Plateau has led to the formation of the world's largest sediment "source–sink" system in the northeastern Indian Ocean, and seafloor sediments record rich environmental and climatic information during the accumulation process, making it an ideal area to reconstruct past sedimentary processes. To reveal fine sediment provenance and climatic implications, we present a sedimentary reconstruction during the past 42 kyr based on clay mineral analyses of sediments from core ADM-159 retrieved from the central Andaman Sea. The clay minerals mainly consist of illite (I, 27%–47%) and kaolinite (K, 8%–37%) with minor smectite (S, 11%–37%) and chlorite (C, 11%–37%). Provenance analyses show that the illite-dominated clay minerals are mainly derived from terrestrial sources of detrital material input from the Irrawaddy River, indicating a primary supply of fine sediment from Myanmar terrestrial material. Considering the stable sediment provenance, S/K, S/(I+C), and the illite chemical index were chosen to reconstruct the transport pattern of the fine fraction sediment over the last 42 kyr. S/K and S/(I+C) showed relatively consistent trends over time with relatively high values at 32–25 and 15–6 ka BP, indicating a strong supply and transport capacity of fine particulate matter. In contrast, relatively low values of S/K and S/(I+C) occurred at 25–15 ka BP, indicating a relatively weak deposition process of fine sediments in the study area. The trends in S/K and S/(I+C) are roughly consistent with the variations in solar radiation. Together with the illite chemical index, these trends indicate that solar activity controlled the weathering and sedimentation of fine-grained sediments. We also found significant periodicities in our clay mineral records at 25.05 and 0.473–0.477 kyr, suggesting that the parameters of the Earth's orbit and solar radiation were potential driving mechanisms of the changes in regional climate. Moreover, monsoon precipitation triggered by the movement of the intertropical convergence zone was another important factor controlling the supply and transport of fine particulate matter in the study area, especially the weak precipitation during the last deglacial period and the relatively strong precipitation during the Holocene, so we could draw a conclusion that precipitation during these periods had significant effects on the weathering, erosion, and transport of fine particulate terrestrial materials over the last 42 kyr. [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]

Paleoclimatic teleconnections between monsoon-dominated regions and the northern Atlantic has been revealed in the tropical Indian Ocean. Millennial-scale climate variability, as registered in Greenland ice cores, was transferred to the low-latitude regions by changes in the Atlantic meridional overturning circulation (AMOC). However, there is still some disputes regarding the mechanism of climatic variation in the tropical Indian Ocean. To explore the interplay responses to regional monsoons and global in the northeastern Indian Ocean, here we present new evidence of trace elements (Mg/Ca and Ba/Ca) and stable isotopes measured from the planktonic foraminifera Globigerinoides ruber (white) in core ADM-159, which was collected from the central Andaman Sea. Twelve accelerator mass spectrometry (AMS) radiocarbon dates of the planktonic foraminifera Neogloboquedrina dutertrei from the core provide a reliable age model. Our results indicate gradual surface warming with several short-lived fluctuations since ~42 kyr ago. The SST during the Last Glacial Maximum (LGM) was ~3 °C colder than the present SST, and a sharp increase in warming beginning at 18.5 cal ka BP indicated the transition from the LGM to the Holocene; these matched well with the warming trend in the Antarctica and the Southern Ocean and the rise in atmospheric CO 2 levels. The seawater δ18O record (defined as δ18O sw , presumably salinity-driven) and the Ba/Ca record, which is a measure of the continental riverine runoff from Myanmar, revealed a prominent millennial-scale variability pattern controlled by the Indian summer monsoon (ISM) as seen in speleothem records. The higher salinity values that suggested weakened ISM precipitation and a decrease in freshwater output from the Irrawaddy-Salween rivers were seen at 41.1 cal ka BP–39.9 cal ka BP, 34.9 cal ka BP–32.8 cal ka BP, 29.3 cal ka BP–28 cal ka BP, 25.7 cal ka BP–23.8 cal ka BP, 19.3 cal ka BP–15.8 cal ka BP, 13 cal ka BP–11.4 cal ka BP, and 4.0 cal ka BP–2.3 cal ka BP, reflecting strong correspondence with cold events in North Atlantic. Thus, this study provides evidence that climatic changes in the tropical Indian Ocean responded well to both regional monsoon and global climate changes, and during that atmospheric CO 2 , solar insolation, and AMOC played the most important roles in those responses. • Millennial-scale climate variability was reconstructed by sea surface temperature and δ18O of seawater in the Andaman Sea. • Indian summer monsoon have been proved linked with northern hemisphere climate events. • Climatic changes in the tropical Indian Ocean responded well to both regional monsoon and global teleconnections. [ABSTRACT FROM AUTHOR]

Studying marine sedimentary archives from the Indian Ocean have provided great opportunities to assess the forcing/response relationship between the Indian monsoons, millennial-scale climate variability as revealed in Greenland ice cores, and possible roles of the Atlantic meridional overturning circulation (AMOC) changes that are most likely responsible for driving both. Here we present new evidence of sea surface temperature (SST) estimates and δ18O of seawater (δ18O sw , presumably salinity-driven) from the paired data of Mg/Ca and δ18O measured from planktonic foraminifer Globigerinoides ruber (white) in core BoB-24 collected from the central Bay of Bengal (BoB), tropical Indian Ocean. Eleven accelerator mass spectrometry (AMS) radiocarbon dates on planktonic foraminifera Neogloboquedrina dutertrei from the core provide a reliable age model. Our results indicate a gradual surface warming with several short-lived fluctuations since ~42 kyr ago, and a ~3 °C cooling during the Last Glacial Maximum (LGM) and a ~3 °C warming from the last glacial to the Holocene. Our δ18O sw revealed an increased salinity during the Marine Isotope Stage (MIS) 2, which is likely attributable to a weakening of Indian Summer Monsoon (ISM) precipitation and associated river discharge in the BoB. Our record also indicates clearly a phase of strengthening ISM during the mid-MIS 3 (37.5–32 ka) as evidenced by low foraminiferal δ18O sw values of ~0.2‰. Lower than present δ18O sw values during the Bølling/Allerød (B/A) event (14.5–12.6 ka) and the early Holocene (10–5 ka) in core BoB-24 indicate lower salinity that in turn suggest enhanced ISM precipitation and increased freshwater output from the Ganges-Meghna-Brahmaputra-Irrawaddy (GMBI) rivers together with peninsular rivers and Irrawaddy-Salween rivers from Myanmar. This study brings data evidence that implies weakened ISM was linked with Northern Hemisphere cooling events, especially during the MIS 2. Furthermore, the millennial-scale hydroclimate changes in the BoB presented in this study support the dynamic role of AMOC in driving a teleconnection between the North Atlantic and Indian Ocean monsoon regions. • Millennial-scale climate variability reconstructed by SST and δ18O sw in the BoB. • Weakened ISM have been proved linked with Northern Hemisphere cooling events. • A teleconnection between the North Atlantic and Indian Ocean by dynamic role of AMOC. [ABSTRACT FROM AUTHOR]