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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]

• 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]

Reconstruction of monsoon evolution in the tropical Indian Ocean and evaluation of its influence on large-scale ocean circulation and sea-air interaction processes can help us understand climate driving mechanisms. Herein, we used a gravity core SO184-10043 to present the marine sedimentary record from the southernmost Sumatra, spanning the past 35 kyr. The age model is well constrained by 12 accelerator mass spectrometry (AMS) radiocarbon dates determined in mixed planktic foraminifera. We also measured sediment grain size and major and trace elements to reconstruct the variations in hydrodynamic conditions and chemical weathering intensity. These data were then used to reveal the evolution of the northwest (Indonesian) monsoon system over the past 35 kyr. The results showed that both monsoon current and chemical weathering coincided with summer insolation in the Northern Hemisphere and responded to glacial-interglacial climate changes in the northern Atlantic. Higher grain-size values of sensitive components, increased chemical index of alteration (CIA), and Ba/Sr ratios, together with lower CaO/MgO ratios, reflect a stronger monsoon current and chemical weathering during the late marine isotope stage 3 and Holocene. Higher intensity of chemical weathering might be attributed to a stronger northwest monsoon carrying warm and moist air from the Asian continent to Indonesian waters. Lower values of sensitive components, CIA, and Ba/Sr, along with higher CaO/MgO values, reveal a weaker monsoon current and lower intensity of chemical weathering during the last glaciation-deglaciation phase, which was controlled by a weaker monsoon system. At a millennial timescale, cold events occurred during the following intervals: 30–26 ka BP, Heinrich Stadial 1 (HS1; 18–15 ka BP), Last Glacial Maximum (LGM; 23–18 ka BP), Younger Dryas (YD; 11–10 ka BP), and 8.2 ka BP. The same cold events were identified from core SO184-10043, indicating a perfect match with climatic cooling in the Northern Hemisphere. We also observed periodicities of ~ 7.9 ka, 3.0–3.1 ka, 2.2–2.3 ka, and ~ 1.0 ka in our core records. These periodicities are coincident with solar-induced climate changes and support the hypothesis that monsoon evolution in the tropical Indian Ocean during the late Pleistocene coincided with the climate change in the Northern Hemisphere. [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]

• An oxic condition was identified by geochemical proxies in the southwestern Sumatra waters over the past 35,000 years. • Semi-precession cycles of marine redox environment in the tropic Indian Ocean were revealed. • Millennial-scale variability of marine redox environment was driven by the ITCZ movement and regional monsoon changes. The marine redox environment (MRE) can affect marine productivity and nutrient cycling, as well as governs material and energy transport. However, its evolution process and driving mechanism in different historical periods revealed significant regional characteristics. Southwestern Sumatra waters, located at the Indo-Pacific Ocean convergence, are an ideal region for studying the evolution of MRE due to significant upwelling and variable productivity levels resulting from the seasonal monsoonal activity. In this study, based on the sediment core SO184–10043, systematic trace element geochemical analysis was conducted for reconstructing the MRE over the past 35,000 years using redox proxies, namely, Ni/Co, U/Th, and biogenic Barium (Ba bio). Ni/Co and U/Th varied in a range of 1–4 and 0.2–1, indicating general oxic conditions with matching productivity levels indicated by Ba bio (ranging from 300 × 10–6 to 580 × 10–6). A comparison with other reconstructed archives indicated that the MRE records of the sediment core in this study were in consistence in responding to the high-latitude climate records with strong semi-precession and millennial fluctuations. Suggestively, these fluctuations correspond to the natural summertime insolation, triggering the latitudinal motions of the Intertropical Convergence Zone (ITCZ), as well as leading to corresponding changes in the seasonal Indian monsoon system. Freshwater lids modulate the mixing effect by acting as barriers and influencing the upwelling development, thereby leading to strong oxic conditions in the MRE. Therefore, robust evidence on the millennial-scale variability in MRE driven by the ITCZ movement and regional monsoon changes in the tropical Indian Ocean is provided by the trace element archives employed in the present study, thereby providing novel insights into the evolution of MRE in response to global and local climate changes. [ABSTRACT FROM AUTHOR]

A 35.30 m-long core (MZ02) that was recovered from a water depth of 32.4 m from the inner shelf mud deposit of the East China Sea is analyzed to determine its sedimentary characteristics, color reflectance, clay mineral content, element geochemistry components and AMS 14 C dating to investigate the sedimentation rate, sediment provenance and paleoclimate evolution during the fast transgression period. Rare earth element and clay mineral proxies indicate that mixed-provenance sediment accumulated in the foreshore–nearshore region at the beginning of the fast transgression period, with a higher sedimentation rate of 5.58 m/ka. From the early Holocene (9.8–9.5 ka B.P.), the sedimentation rate declined by approximately 1.73 m/ka, and the sediment provenance obviously changed. The silt fraction resembled that of Taiwan's mountainous rivers and the clay fraction was primarily transported from the Yangtze River. A multiple proxy system including sediment redness (a*), chemical index of alteration (CIA), clay mineral ratio (smectite/kaolinite), and major and trace element ratios (CaO/MgO, Ba/Sr), also provides a good paleoclimate record during the fast transgression period, which can be divided into three units. All the proxies barely changed during Unit I (12.88–10.85 ka B.P.), revealing that the climate remained relatively stable. Obvious fluctuations occurred during Unit II (10.85–10.05 ka B.P.), and the temperature kept decreasing for more than 1 ka until the Younger Dryas event, showing a notable regional response to global climate changes. A continuous warming trend resumed again during Unit III (10.05–8.15 ka B.P.), which may mark the threshold of the Holocene warm period. In addition, we find significant 80-yr, 89-yr and 100-yr cycles in the CIA, CaO/MgO and Ba/Sr records, which imply the possible influence of solar activity on regional climate change during the fast transgression period in the Asian margin region. [ABSTRACT FROM AUTHOR]

Surface seawater stratification shows a sensitive response to solar insolation and large-scale ocean current, further playing an important role in the air-sea interactions at different time scales. However, the variation of surface seawater structure and its driving mechanism in the tropical Indian Ocean is poorly understood. We present a new record of thermocline temperature (TWT) obtained using oxygen isotope and Mg/Ca-temperature of the planktonic foraminifer Pulleniatina obliquiloculata (P. obliquiloculata) from core BoB-24 in the central Bay of Bengal (BoB). The results indicate that TWT rose rapidly from the Younger Dryas (YD) and persisted at a peak temperature value of 22.5 °C between 10 and 7 cal ka BP, and subsequently reduced by 1.5 °C in the middle Holocene period. The temporal variability of TWT occurred following the boreal summer insolation, associated with tropical climate changes such as the movement of the Inter-tropical Convergence Zone (ITCZ) as well as relevant changes of seasonal Indian monsoons. During the YD period, the southward movement of ITCZ and strengthened Indian winter monsoon (IWM) influenced the deepening of pycnocline, which caused subsurface warming and decreased stratification. During the middle Holocene, the northward return of ITCZ and strengthening of Indian summer monsoon (ISM) led to a stronger surface water stratification and present cooling trend of optimum TWT (10–7 cal ka BP). Furthermore, the millennial TWT changes presented in this study revealed a close link with North Atlantic climate changes, indicating a dynamic action of Atlantic meridional overturning circulation (AMOC). • Variabilities of thermocline temperature and oxygen isotope over the last 15 kyr were reconstructed in the Bay of Bengal. • Monsoon-driven salinity changes influence the thermal stratification by tropical dynamic changes. • Millennial scale variability of surface stratification was driven by Atlantic meridional overturning circulation. [ABSTRACT FROM AUTHOR]

In the Indian monsoon realm, spatial homogeneity of hydroclimate response to glacial abrupt climate events in the North Atlantic Ocean and its underlying mechanism are contentious. Here we reconstruct sea surface temperature (SST) and seawater oxygen isotope (δ18O sw) in the central Andaman Sea, which span over the past 26,000 years, to investigate the potential driving mechanism of millennial-scale climate changes in tropical Indian Ocean. Our results demonstrate that millennial-scale SST and δ18O sw changes during the last deglaciation are associated with changes in Asian monsoon system which follows North Atlantic climate changes. In particular, during the transition from BØlling/AllerØd (B/A) to Younger Dryas (YD), the strengthening of East Asian winter monsoon (EAWM) promotes southward invasion of northern cold air masses to Indo-China Peninsula, cooling the Andaman Sea. Meanwhile, the enriching δ18O sw is a consequence of reducing local rainfall amount and Irrawaddy River inflow due to a weakening Indian summer monsoon (ISM). With aid of an isotope-enabled climate model, our results further demonstrate that the changes in EAWM and ISM during B/A-YD transition are closely coupled with variations of Atlantic meridional overturning circulation (AMOC), corroborating its pivotal role in millennial-scale changes in tropical Indian Ocean hydroclimate during the last deglaciation. • Andaman Sea characterizes abrupt changes in sea surface temperature and δ18O of seawater during the last deglaciation. • δ18O sw and precipitation are characterized by spatial homogeneity of response to abrupt climate change in North Atlantic. • Millennial-scale temperature changes in Andaman Sea show a local feature controlled by East Asian winter monsoon. [ABSTRACT FROM AUTHOR]

The ocean heat content (OHC) and associated surface stratification in tropical oceans are ideal variables to monitor global climate change. However, the variations in surface stratification of the tropical Indian Ocean at the millennial time scale have been less understood. In this context, the present study aimed at reconstructing the sea surface temperature (SST) and thermocline water temperature (TWT) using Mg/Ca of planktonic foraminifera in the sediments of the Andaman Sea, which is one of the hot centers in the Indo-Pacific warm pool (IPWP) over the past 42 ka. The study results confirm the SST changes are consistent in response to the high-latitude temperature records with strong sub-orbital and millennial variations, while the TWT patterns trend remarkably different from the millennial-scale SST and show the variations correspond to the natural summer insolation that triggers the latitudinal movements of the Intertropical Convergence Zone (ITCZ). Furthermore, salinity influences the thermal differences (ΔT=SST-TWT) by varying the vertical temperature and stratification. Analysis of available data shows that the mean northward position of ITCZ would input more freshwater into the Andaman Sea. Freshwater lids can reduce mixing by acting as effective barriers and preventing heat from transferring from the surface to the subsurface, thereby causing subsurface cooling and increased stratification. In contrast, more southward ITCZ (boreal winter monsoon) supplies less freshwater into the Andaman Sea. A highly saline surface water and air cooling promotes mixing and subsurface warming, resulting in decreased stratification. The study results reveal a millennial-scale vertical thermal seesaw synchronizing in the tropical Indian Ocean with abrupt Atlantic meridional overturning circulation (AMOC) changes. During the Bolling-Allerod (B/A) warming period, the dynamic AMOC maintains the surface water stratification by controlling the subsurface cooling processes with increased precipitation and freshwater brought by the northward ITCZ. In contrast, Younger Dryas (YD) and Heinrich events (H) are characterized by reduced summer monsoon precipitation associated with the sluggish AMOC and southward ITCZ, resulting in less stratification and subsurface warming in the Andaman Sea. The thermal proxy records adopted in the study afford robust evidence on the millennial-scale variability in surface stratification driven synchronously by AMOC and regional evaporation vs. precipitation changes in the tropical Indian Ocean, offering new insights into the impacts of the IPWP OHC on abrupt climate changes. • Millennial-scale climate variability was reconstructed by SST and TWT in the Andaman Sea. • Salinity influences the thermal differences (ΔT) by varying the vertical temperature and stratification. • Millennial scale variability of surface stratification was driven synchronously by AMOC and tropical dynamic changes. [ABSTRACT FROM AUTHOR]

We present a paleoclimatic reconstruction for the Holocene by clay mineral analyses of sediments from core MZ02 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). The clay minerals mainly consist of illite (66%–79%) and chlorite (12%–19%), with minor kaolinite (7%–13%) and smectite (0–6%). Provenance analysis suggests that the illite-dominated clay minerals were derived mainly from the detrital outputs of the Changjiang, Minjiang, and small rivers from Taiwan Island. Our study indicates that the sea level rise since the last glacial, the strength of the Taiwan Warm Current (TWC) and Chinese Coastal Current (CCC) have controlled the dispersal and deposition of clay minerals on the ECS, that in turn determined the clay mineral compositions in the core sediments. During 13,000–9500 BP, due to the lower sea level and shorter distance between these three estuaries and core MZ02, fine sediments on the inner shelf of the ECS were primarily supplied by mixed provenances from the Changjiang, Taiwanese, and Minjiang rivers. During the early Holocene (9500–6200 BP), stronger sediment reworking and erosion at the shelf edge was responsible for the increased lateral transport of fine sediments in the ECS, which lead to a dominance of the sediment source from the Changjiang, while the Taiwanese and Minjiang rivers only provided minor components of detrital sediment to the shelf. Increased strength of TWC might have played an important role in the sediment dispersal and deposition on the inner shelf of the ECS during 6200–2400 BP, with a dominance of more than 60% sediments transported from Taiwanese rivers. Furthermore, our study implies that the Asian monsoon and the weakening of TWC were linked to the abrupt increase of Changjiang and Minjiang derived terrigenous detritus materials since 2400 BP. [ABSTRACT FROM AUTHOR]

Abstract: We present a paleoclimatic reconstruction of the mid-Holocene by geochemical analysis of a sediment core MZ01 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). Our results show that the downcore geochemical variations in the sediments of the core provide a link to historical climate changes. Relatively higher ratios of CIA, Ba/Sr and a lower ratio of CaO/MgO coincide with major regional warm and humid climate episodes, and vice versa. Therefore, these geochemical indicators are useful in reconstructing the paleoclimate in eastern China. Using the geochemical records of core MZ01, which are well constrained by AMS 14C dating, we found that from 8300yr BP to 4200yr BP the regional climate was moderately warm and humid, and from 4200yr BP to 2300yr BP the climate was cool and dry, with large fluctuations between cool–dry (3700yr BP, 2850yr BP and 2400yr BP) and warm-wet (3250yr BP and 2650yr BP). Since 2300yr BP, our records indicate that the climate has gradually become warmer, although a cold event centered at around 250yr BP (the Little Ice Age, LIA) interrupted this warming trend. We also found significant 238yr cycles in our CIA records that imply a possible solar influence on the regional climate changes since the mid-Holocene. [Copyright &y& Elsevier]

AMS14C dating and analysis of grain size, major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea. Based on the environmentally sensitive grain size, clay mineral and major element assemblages, the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed. These three proxies, mean grain size (>9.71 µm), chemical index of alteration (CIA) and ratio of smectite to kaolinite in particular, show similar fluctuation patterns. Furthermore, 10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene; these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon. The cooling events correlated well with the results of the δ 18 O curves of the Dunde ice core and GISP2, which therefore revealed a regional response to global climate change. Four stages of the East Asia winter monsoon were identified, i.e. 8300-6300 a BP, strong and unstable; 6300-3800 a BP, strong but stable; 3800-1400 a BP, weak and unstable; after 1400 a BP, weak but stable. [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]

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]

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, as the largest submarine fan in the world, receives a large amount of sediments discharged from the Himalayas through the Ganges-Brahmaputra (G-B) river system. However, previous studies of this system seldom focused on the role of channels, which are widely developed in the Bengal Fan, in sediment transportation over the last glacial cycle. Here, we discuss the coupled sedimentary archive in two gravity cores along the Active Channel in the Bengal Fan. Our findings are based on grain size, clay minerals, and Sr and Nd isotope compositions of these two sediment cores. End-member modeling of grain-size data reveals that the intermediate end-member represents the flux of distal fluvial particles from the G-B river system, the fine end-member denotes regional sediment supply of weathered volcanic materials, especially from the eastern Indian Peninsula, and the coarse end-member probably reflects nearby terrigenous input, aeolian input and/or volcanic glass. Sediment provenance analysis based on clay minerals, and Sr and Nd isotopes confirmed sediment supply from the G-B river system which was characterized by high illite percentage, high 87Sr/86Sr ratios and low ε Nd values, especially during five stages (50–45 ka, 42–37 ka, 31–28.5 ka, 24–20 ka and 14–9 ka). During these stages, heavy fine-grained sediment supply from the G-B river system was discharged into the study area under the influence of climate change rather than sea-level fluctuation, additionally emphasizing the importance of channels in the sediment transport process. Moreover, we find a significant alteration of sediment sources at ∼26 ka, which may be related to conversion of the deep-water currents in the Bay of Bengal. • There is staged sediment supply from the G-B Rivers into the Bay of Bengal. • Heavy sediment supply of the G-B Rivers was affected by climate change. • The channels developed on the Bengal Fan are important in the sediment transport process. • Sediment source change at ∼26 ka may be related to conversion of deep-water currents. [ABSTRACT FROM AUTHOR]

The Indo-Pacific warm pool (IPWP) is an area hosting key tropical climate processes such as the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). The tropical climate processes, via various feedback mechanisms, control the surface ocean climate in the Indian Ocean and its surrounding continents on annual to inter-annual timescales. However, little has been known about how the tropical processes are effective forcing climate mechanism over longer timescales. Here we presented a reconstruction of the spatiotemporal pattern of sea surface temperature (SST) with inferred hydroclimate changes since the early Holocene (∼11ka), using proxies of planktonic foraminifer shell Mg/Ca, organic biomarker (TEX 86 ), foraminifer oxygen isotopes, and a terrigenous BIT index measured from a 220 cm long Core BS24 (2.724041°N, 97.010943°E, 1015 m water depth) which was taken offshore of northwest Sumatra in the eastern Indian Ocean. With an age model of 13 AMS 14 C dating by the uses of planktonic foraminiferal shells from the core, the TEX 86 H temperatures of BS24 show as summer-weighted, and reflect integrated thermal effects from the surface to thermocline water, while the Mg/Ca temperature of BS24 better reflects mean annual SST. Our results, along with a regional synthesis of published SST records from the IPWP, suggest that the IPWP has migrated eastwardly since the mid-Holocene (∼5ka). In phase with this eastward migration, the IPWP SSTs have decreased, but the upwelling in the eastern Indian Ocean appears to have been a persistent feature since the mid-Holocene. Our Empirical Orthogonal Function (EOF) analysis on the compiled IPWP SST records indicates two dominant modes of spatio-temporal variability of surface hydrographes in the IPWP that are attributed to a combined effect of orbital and solar forcing, with expressions analogous to the Indian ocean basin-wide mode (IOBM) and the Indian Ocean dipole model (IOD). [ABSTRACT FROM AUTHOR]

[Display omitted] • The sedimentary evolution and provenance variation of Central Yellow Sea Mud was the result of sea level rising at the begin of Holocene and the established shelf circulation after 7.0 ka. • Drastic environmental changes in the Yellow River basin after 4.0 ka induced by weakening of East Asian Summer Monsoon and enhanced human activities increased the sediment accumulation in the Central Yellow Sea Mud. • The sedimentation of Central Yellow Sea Mud was controlled by the sediment supply under the regulation of monsoon climate and human activities after 4.0 ka. The Central Yellow Sea Mud (CYSM) archived important signals of regional environment and climate changes during the Holocene. We performed high-resolution analysis of two sediment cores taken from the CYSM, including measurements of radiocarbon chronology and grain size, as well as the mineralogical and geochemical measurements on the sediment samples. The results indicate that the Yellow River were likely a dominant source of the CYSM before 6.8 ka BP, with minimal contributions from the local small rivers in the Shandong Peninsula and Korean Peninsula, as confirmed by the mineralogical and geochemical evidences. After 6.8 ka BP, the fine-grained sediments accumulated in the CYSM presented a mixture of those from both the Yangtze and Yellow River with an individual contribution of 55 ± 8% and 45 ± 6%, respectively, as the sea level reached its highstand and initiated the establishment of modern shelf circulation. The drastic environmental changes in the Yellow River basin after 4.0 ka BP driven by the weakened East Asian Summer Monsoon and enhanced human activities that significantly increased the sediment yield from the Chinese Loess Plateau should be responsible for the abrupt increase in the fine-grained sediment (<2 μm) accumulation in the CYSM. After 1.4 ka BP the decrease in precipitation in the Yellow River basin resulted in the imbalance between sediment yield and river runoff, which perhaps induced lower channel aggradation and frequent avulsions, and consequently decreased the accumulation rate of the Yellow River-derived sediment in the CYSM. During the Holocene, the rising sea level played a primary role in shaping the sedimentation of the CYSM including the retreated coastline and establishment of shelf circulation system, whereas the monsoonal climate and human activities dominated the terrestrial sediment supply and accumulation in the CYSM after 4.0 ka BP. [ABSTRACT FROM AUTHOR]

Paleoenvironment and paleoclimate change in the Andaman Sea during the last 26 ka were reconstructed from high-resolution records of grain-size, major elements and Sr–Nd isotopes in core ADM-9. The values of ε Nd (0) and 87 Sr/ 86 Sr were in good agreement with those of Irrawaddy River sediments, indicating a common source of origin. Two sensitive grain-size intervals (3.4–7.5 and 16.8–21.2 μm) were identified; the former was controlled primarily by sea-level change, whereas the latter was related to Irrawaddy River discharge and South-west Current transport driven by the Indian Summer Monsoon (ISM). Proxies of chemical weathering (K/Al) and terrigenous input (Ti/Ca) coupled with sensitive grain-size interval (16.8–21.2 μm population) revealed that the ISM was weak during ∼15–26 ka BP and then strengthened gradually to a maximum during ∼7–9 ka BP; subsequently, the ISM exhibited a generally declining trend to ∼2 ka BP. The variation in the ISM recorded in this work is consistent with ISM variations observed in an open area in the northern Indian Ocean and adjacent continents, implying the evolution of the Asia Summer Monsoon since 26 ka. [ABSTRACT FROM AUTHOR]

This study investigates Holocene sedimentary evolution and hypoxia development using borehole cores CJK06 and CJK09, in combination with other published core data. Based on lithology and microfossil (benthic foraminifera) characteristics, seven types of sedimentary facies were identified from the base upward: river, tidal flat, tide-influenced river, transgressive lag, estuary, inner-shelf, and prodelta. Isochronous correlation among the cores was established relying on accelerator mass spectrometry 14C dates. Facies succession indicates that a weak progradation occurred in coastal environments (12–10 ka BP) due to the Younger Dryas-induced deceleration of sea-level rise; rapid deposition locally occurred in the southern marginal area of tide-dominated estuary environments (10–8 ka BP), likely due to the junction of the Yangtze and Qiantangjiang River currents; and marine current-induced fluid mudflows prevailed in the shallow marine environments (8–1 ka BP), with the cooling climates of 5–1 ka BP. Furthermore, prodelta and shallow marine environments co-occurred with an uneven progradation of the delta within the last 1 ka, while deposition occurred just inside the more southern, delta-influenced area. The occurrence of euryhaline benthic foraminifera suggests that an enhanced freshwater discharge of the mid-Holocene (8–5 ka BP) was followed by a sharp decline in the late Holocene (5–1 ka BP) with climate change. The occurrence of cold-water benthic foraminifera indicates a severe cold-water condition during the mid-Holocene due to the intrusion of upwelling currents triggered by the propelling force of warm currents and summer monsoon winds. In addition, the occurrence of low-oxygen foraminiferal assemblages reveals that hypoxia has developed since 10 ka BP in stages consistent with the sedimentary evolution: localized hypoxia formation coincident with the southern depocenter during the early Holocene (10–8 ka BP); severe hypoxia with enhanced freshwater discharge and upwelling current intrusion during the mid-Holocene; and weakened hypoxia of the late Holocene, mainly due to the sharp decline in freshwater discharge. Within 1 ka BP, freshwater discharge from the approaching river mouth and increased nutrient inputs from enhanced human activities on land have contributed to the prevalence of hypoxia, especially in the southern deltaic area. Overall, it was revealed that the freshwater discharge modulated with climate variations and delta progradation plays a primary role in controlling the sedimentary evolution and hypoxia development during the mid-late Holocene. • Gravity flows (fluid mudflow) prevailed during the late Holocene (5–1 ka BP). • Holocene freshwater discharge was enhanced (8–5 ka BP) and then sharply declined. • Severe upwelling current intrusion occurred during the mid-Holocene (8–5 ka BP). • Hypoxia boomed during the mid-Holocene (8–5 ka BP). [ABSTRACT FROM AUTHOR]