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We have measured Cd/Ca ratios of several benthic foraminiferal species and studied benthic foraminiferal assemblages on two cores from the northern Indian Ocean (Arabian Sea and northern Bay of Bengal, BoB), in order to reconstruct variations in intermediate-water circulation and paleo-nutrient content since the last deglaciation. Intermediate water Cdw records estimated from the benthic Cd/Ca reflect past changes in surface productivity and/or intermediate–bottom-water ventilation. The benthic foraminiferal assemblages are consistent with the geochemical data. These results suggest that during the last deglaciation, Cdw variability was primarily driven by changes in intermediate-water properties, indicating an enhanced ventilation of intermediate–bottom water masses during both Heinrich Stadial 1 and the Younger Dryas (HS1 and YD, respectively). During the Holocene, however, surface primary productivity appears to have influenced Cdw more than intermediate water mass properties. This is evident during the early Holocene (from 10 to 6 cal ka) when benthic foraminiferal assemblages indicate that surface primary productivity was low, resulting in low intermediate-water Cdw at both sites. Then, from ∼ 5.2 to 2.4 cal ka, surface productivity increased markedly, causing a significant increase in the intermediate-water Cdw in the southeastern Arabian Sea and the northeastern BoB. The comparison of intermediate-water Cdw records with previous reconstructions of past Indian monsoon evolution during the Holocene suggests a direct control of intermediate-water Cdw by monsoon-induced changes in upper-water stratification and surface primary productivity.

We investigate the phased evolution and variation of the South Asian monsoon and resulting weathering intensity and physical erosion in the Himalaya–Karakoram Mountains since late Pliocene time (c.3.4 Ma) using a comprehensive approach. Neodymium and strontium isotopic compositions and single-grain zircon U–Pb age spectra reveal the sources of the deposits in the east Arabian Sea, and show a combination of sources from the Himalaya and the Karakoram–Kohistan–Ladakh Mountains, with sediments from the Indian Peninsula such as the Deccan Traps or Craton. We interpret shifts in the sediment sources to have been forced by sea-level changes that correlate with South Asian monsoon rainfall variation since late Pliocene time. We collected 908 samples from the International Ocean Discovery Program Hole U1456A, which was drilled in the east Arabian Sea. Time series of hematite content and grain size of the sediments were examined downcore. We found South Asian monsoon precipitation and weathering intensity experienced three phases from late Pliocene time. Lower monsoon precipitation, with a lower variability and strong weathering intensity, occurred during 3.4–2.4 Ma; an increased and more variable South Asian monsoon rainfall, along with strengthened but fluctuating weathering intensity, occurred at 1.8–1.1 Ma; and a reduced rainfall with lower South Asian monsoon precipitation variability and moderate weathering intensity marked the period 1.1–0.1 Ma. Maximum entropy spectral analysis and wavelet transform show that there were orbital-dominated cycles of periodsc.100 andc.41 ka in these proxy-based time series. We propose that the monsoon, sea level, global temperature and insolation together forced the weathering and erosion in SW Asia.

Nd raw data unpublished.

Reconstructing the Plio-Pleistocene sedimentary history of the Yellow Sea, is important for understanding the long-term influence of the Yellow River (Huanghe) and/or Yangtze River (Changjiang) on the Asian marginal seas and to further constrain any links between river development, regional paleoenvironmental change, tectonic deformation and/or global climate change. Here we present the first high-resolution clay mineral record combined with Sr-Nd isotopic compositions from a 300-m long sediment core recovered in the western South Yellow Sea. Our study suggests that large-scale transgression in the Yellow Sea occurred after ∼0.8 Ma, possibly related to tectonic subsidence of eastern China coast and the Min-Zhe Uplift. In contrast, the sedimentary environment of Bohai and Yellow Seas was mainly dominated by fluvial/lacustrine deposits at 3.5–0.8 Ma. Provenance analysis suggests a major change in sediment provenance from the Yangtze River to the Yellow River at ∼0.8 Ma, which corresponds to the timing of the final integration of the Yellow River in its present form. At the same time the major channels of the Yangtze River migrated from the South Yellow Sea to the modern Yangtze River delta due to the subsidence of east China coast. The consistence in timing of the provenance transition and large-scale regional marine transgression suggests that tectonic deformation, rather than climate change, is the first-order control on the evolution of the Yellow and Yangtze Rivers and sedimentary environmental change in the Bohai and Yellow Seas.

The intensity of turbidite sedimentation over long timescales is driven by sea-level change, tectonically driven rock uplift and climatically modulated sediment delivery rates. This study focuses on understanding the effect of sea-level fluctuations and climatic variability on grain-size variations. The grain size and environmental magnetic parameters of Arabian Sea sediments have been documented using 203 samples, spanning the last 200 ka, obtained from International Ocean Discovery Program (IODP) Site U1457. Grain-size end-member modelling suggests that between ~200 and 130 ka there was an increase in the coarse silt fraction caused by sediment transport following reworking of the Indus Fan and development of deep-sea canyons. The sediment size and enhanced magnetic susceptibility indicate a dominant flux of terrestrial sediments. Sedimentation in the distal Indus Fan atc. 200–130 ka was driven by a drop in sea level that lowered the base level in the Indus and Narmada river systems. The low sea-stand caused incision in the Indus delta, canyons and fan area, which resulted in the transportation of coarser sediment at the drilling site. Magnetic susceptibility and other associated magnetic parameters suggest a large fraction of the sediment was supplied by the Narmada River during ~200–130 ka. Since ~130 ka, clay-dominated sedimentation is attributed to the rise in sea level due to warm and wet climate.

Clay mineral assemblages at International Ocean Discovery Program Expedition 355 Site U1456 drilled in the eastern Arabian Sea have been investigated to reveal the sediment provenances and reconstruct the erosion/weathering patterns in the western Himalaya and Indian subcontinent, thus constraining the evolution of the Indian summer monsoon and its forcing mechanism since 1.2 Ma. The clay mineral assemblages at Site U1456 mainly comprise smectite (with an average value of 59%) and illite (with an average value of 33%), with chlorite (with an average value of 5%) and kaolinite (with an average value of 3%) as minor constituents. In terms of sediment provenance, our results indicate that illite and chlorite are predominantly derived from the Indus River, which originates from the western Himalaya and Karakoram, while smectite is primarily sourced from the Narmada River and Tapti River in the Deccan Traps, with a non-negligible contribution from the Indus River in some cases. Variations in smectite/(illite + chlorite) ratio are ultimately controlled by the Indian summer monsoon, which is characterized by approximate glacial/interglacial cyclicity, showing higher values (i.e., enhanced chemical weathering) during interglacial periods. In addition, a major shift in smectite/(illite + chlorite) ratio at 0.9 Ma is correlated to the Mid-Pleistocene Transition (∼1.2–0.9 Ma). Both the Marine Isotope Stage 13 event (533–478 ka) and the Mid-Brunhes Event (∼430 ka) are also recorded in the clay mineral proxies. Based on the spectral analysis, smectite/(illite + chlorite) ratio displays a transition from nonprimary periodicity (29-kyr) to strong eccentricity (100-kyr) and precession (22-kyr) periodicities at approximately 0.9 Ma, which corresponds to the Mid-Pleistocene Transition. Our study indicates that the variability of the Indian summer monsoon at orbital timescales is controlled by high-latitude (i.e., ice volume) and low-latitude (i.e., summer insolation) processes.

Long marine sequences deposited in the Arabian Sea are suitable to study the orbital sensitivity of sediment dynamics from a source-to-sink perspective. The clay mineralogy and Sr Nd isotopic compositions have been analyzed for the detrital fraction of sediments from IODP Site U1457 located in the Laxmi basin, eastern Arabian Sea to constrain the sediment sources and reconstruct a high-resolution record of sediment export to the Indus deep-sea fan over the past 600 kyr. The 87Sr/86Sr ratio (varying from 0.7154 to 0.7255) and eNd (varying from −12.9 to −9.5) imply a mixing of sediments derived from not only the Indus River but also the rivers draining the Deccan Traps. The variations in the smectite/(illite + chlorite) ratio combined with Sr Nd isotopes permit the reconstruction of past changes in the relative proportions of sediments derived from the Indus River (mainly illite, chlorite and kaolinite) and the Deccan Traps (smectite). The wavelet and cross-spectral analyses further reveal that sediment transport to the eastern Arabian Sea since 600 kyr is mainly dominated by sea-level variations in the eccentricity (100-kyr) band, while the Indian summer monsoon might contribute moderately to the precession (23-kyr) band. The eNd and turbidite frequency indicate that more turbidite events are associated with Indus River-sourced sediments at IODP Site U1457 during sea-level lowstands, which might reflect a reconnection of deep-sea channels to the Indus River mouth and/or reworking of previously deposited Indus River sediments located northward.

As the device feature size shrinks, the dissipation of power increases and further raises the carrier and lattice temperature, which finally affects device performance. In this paper, we analyze the comprehensive influence of the self-heating effect and hot carrier injection (HCI) using TCAD simulations. Based on the hydrodynamic and thermodynamic models, it is demonstrated that the thermal surface resistance had a positive impact on the carrier and lattice temperature and that the drain saturation current is reduced dramatically due to the self-heating effect. Moreover, the impact of HCI on device performance is discussed. Finally, it is concluded that the self-heating effect exacerbates the influence of HCI on device characteristics.

International audience; Changes in terrigenous organic matter (OM) input, productivity and the associated bottom-water redox conditions, together with forcing mechanisms and global carbon cycle implications of such variations, on the western margin of the Western Pacific Warm Pool (WPWP) during the Quaternary remain controversial. In this study, we reconstructed the hydrological dynamics, terrigenous OM input, productivity, and deep-sea redox conditions using one core from the continental slope of the Philippine Sea. The new data were integrated with published proxies from the same core and two additional cores from the abyssal Philippine Sea. The results exhibited noticeable variations in the abovementioned indicators, in correspondence to changes in the supply of terrigenous material. The continental slope deposition featured signals of strong physical erosion and chemical weathering of unconsolidated sediments on the exposed continental shelf during the Quaternary sea-level lowstands, which significantly contributed to increased terrigenous OM input and productivity and, in turn, decreased bottom-water oxygenation and atmospheric CO2 concentrations. In the abyssal Philippine Sea, increased Asian dust-driven OM input and productivity also acted as a sink of atmospheric CO2 during sea-level lowstands. Analysis of the data suggested that the enhanced terrigenous OM input and biological pump and thus the decreased dissolved oxygen level of the bottom water on the western margin of the WPWP played important roles in modifying the global carbon cycle during sea-level lowstands. In contrast, the influence of hydrological dynamics on terrigenous OM input, productivity, and redox conditions therein during the Quaternary was limited.

We present a new set of clay mineral and grain-size data for the siliciclastic sediment fraction from International Ocean Discovery Program (IODP) Site U1456 located in the eastern Arabian Sea to reconstruct the variabilities in the continental erosion and weathering intensity in the western Himalaya, elucidate the sediment source-to-sink processes and discuss the potential controls underlying these changes since 3.7 Ma. The clay minerals mainly consist of smectite (0–90%, average 44%) and illite (3–90%, average 44%), with chlorite (1–26%, average 7%) and kaolinite (0–19%, average 5%) as minor components. The compositional variations in the clay minerals at IODP Site U1456 suggest four phases of sediment provenance: the Indus River (phase 1, 3.7–3.2 Ma), the Indus River and Deccan Traps (phase 2, 3.2–2.6 Ma), the Indus River (phase 3, 2.6–1.2 Ma) and the Indus River and Deccan Traps (phase 4, 1.2–0 Ma). These provenance changes since 3.7 Ma can be correlated with variations in the Indian summer monsoon intensity. The siliciclastic sediments in the eastern Arabian Sea were mainly derived from the Indus River when the Indian summer monsoon was generally weak. In contrast, when the Indian summer monsoon intensified, the siliciclastic sediment supply from the Deccan Traps increased. In particular, this study shows that the smectite/(illite+chlorite) ratio is a sensitive tool for reconstructing the history of the variation in the Indian summer monsoon intensity over the continents surrounding the Arabian Sea since 3.7 Ma.

Mineralogical and geochemical analyses conducted on cores located on the active channel-levee system of the northern Bengal Fan are used to establish changes in the weathering pattern and the sediment transport of the Himalayan system, and evaluate the effect of Indian summer monsoon rainfall during the Holocene. Our data indicate that during the Holocene, sediments from the northern Bengal Fan originate mainly from the G-B river system without any significant changes in the relative contribution of these rivers. From 9.8 to around 6 ka, relatively low smectite/(illite1chlorite) ratios and relatively high K/Si* ratios indicate high physical denudation rates of the Himalayan highlands together with a rapid transfer of the detrital material to the Bengal Fan. The period between 9.2 and 7 ka is associated to lower values of K/ Si* and corresponds to the maximum of Indian monsoon rainfall which indicates a more important chemical weathering material that rapidly transits by the G-B river system without a long storage in the Indo-Gangetic plain. From 6.0 ka to present day, higher smectite/(illite1chlorite) ratio and lower K/Si* ratio document a gradual increase of sediments originated from the Indo-Gangetic plain, characterized by higher degree of chemical weathering. During the last 2.5 ka, the drastic increase in the smectite/(illite1chlorite) ratio could be associated to enhanced alteration of the plain soils due to anthropogenic activity. The comparison of mineralogical and geochemical data with previous reconstructions of the Indian monsoon dynamic indicates a rapid response of erosion and sediment transfer of the G-B river system to changes of monsoon rainfall intensity.

Made available in DSpace on 2020-12-10T17:04:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Charles T. McCord Jr Chair in Petroleum Geology at Louisiana State University Ministry of Earth Sciences, Government of India National Centre for Polar and Ocean Research (NCPOR) National Research Foundation of Korea CSIR-National Institute of Oceanography, India A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in volume all but one other known complex on passive margins worldwide. The complex, named the Nataraja Slide, was drilled by International Ocean Discovery Program (IODP) Expedition 355 in two locations where it is similar to 300 m (Site U1456) and similar to 200 m thick (Site U1457). The top of this mass-transport complex is defined by the presence of both reworked microfossil assemblages and deformation structures, such as folding and faulting. The deposit consists of two main phases of mass wasting, each consisting of smaller pulses, with generally fining-upward cycles, all emplaced just prior to 10.8 Ma based on biostratigraphy. The base of the deposit at each site is composed largely of matrix-supported carbonate breccia that is interpreted as the product of debris-flows. In the first phase, these breccias alternate with well-sorted calcar-enites deposited from a high-energy current, coherent limestone blocks that are derived directly from the Indian continental margin, and a few clastic mudstone beds. In the second phase, at the top of the deposit, muddy turbidites dominate and become increasingly more siliciclastic. At Site U1456, where both phases are seen, a 20-m section of hemipelagic mudstone is present, overlain by a similar to 40-m-thick section of calcarenite and slumped interbedded mud and siltstone. Bulk sediment geochemistry, heavy-mineral analysis, clay mineralogy, isotope geochemistry, and detrital zircon U-Pb ages constrain the provenance of the clastic, muddy material to being reworked, Indus-derived sediment, with input from western Indian rivers (e.g., Narmada and Tapti rivers), and some material from the Deccan Traps. The carbonate blocks found within the breccias are shallow-water limestones from the outer western Indian continental shelf, which was oversteepened from enhanced clastic sediment delivery during the mid-Miocene. The final emplacement of the material was likely related to seismicity as there are modern intraplate earthquakes close to the source of the slide. Although we hypothesize that this area is at low risk for future mass wasting events, it should be noted that other oversteepened continental margins around the world could be at risk for mass failure as large as the Nataraja Slide. Louisiana State Univ, Dept Geol & Geophys, E253 Howe Russell Kniffen Geosci Complex, Baton Rouge, LA 70803 USA Texas A&M Univ, Int Ocean Discovery Program, 1000 Discovery Dr, College Stn, TX 77845 USA Woods Hole Oceanog Inst, Dept Geol & Geophys, Woods Hole, MA 02543 USA UCL, Dept Earth Sci, Gower St, London WC1E 6BT, England Univ Toulouse 3 Paul Sabatier, Geosci Environm Toulouse, 14 Ave Edouard Belin, F-31400 Toulouse, France GeoSep Serv, 1521 Pine Cone Rd, Moscow, ID 83843 USA Univ Queensland, Sch Earth & Environm Sci, St Lucia, Qld 4072, Australia Natl Ctr Polar & Ocean Res, Vasco Da Gama 403804, Goa, India Univ Milano Bicocca, Dept Earth & Environm Sci, Piazza Sci 4, I-20126 Milan, Italy Purdue Univ, Dept Earth Atmospher & Planetary Sci, 550 Stadium Mall Dr, W Lafayette, IN 47907 USA Univ Birmingham, Sch Geog Earth & Environm Sci, Birmingham B15 2TT, W Midlands, England Macquarie Univ, Fac Sci & Engn, Dept Earth & Planetary Sci, N Ryde, NSW 2109, Australia Ohio State Univ, Sch Earth Sci, 275 Mendenhall Lab,125 South Oval Mall, Columbus, OH 43210 USA Birbal Sahni Inst Palaeosci, 53 Univ Rd, Lucknow 226007, Uttar Pradesh, India Univ Bremen, MARUM, Leobener Str, D-28359 Bremen, Germany Kochi Univ, Dept Nat Environm Sci, 2-5-1 Akebono Cho, Kochi 7808520, Japan Pusan Natl Univ, Div Earth Environm Syst, Busan 60973, South Korea Wadia Inst Himalayan Geol, 33 GMS Rd, Dehra Dun 248001, Uttrakhand, India Natl Inst Ocean Technol, Marine Biotechnol Dept, Velacheiy Tambaram Main Rd, Chennai 600100, Tamil Nadu, India Columbia Univ, Ctr Climate Syst Res, 2880 Broadway, New York, NY 10025 USA Nanjing Univ, Sch Geog & Oceanog Sci, 163 Xianlin Ave, Nanjing 210023, Jiangsu, Peoples R China Oregon State Univ, Coll Earth Ocean & Atmospher Sci, 104 CEOAS Adm Bldg, Corvallis, OR 97331 USA Natl Ctr Earth Sci Studies, Geosci Div, Aakkulam Trivandrum 695031, India Natl Inst Oceanog, Geol Oceanog Div, Panaji 403004, Goa, India Oil & Nat Gas Commiss, 11 High,Bandra Sion Link Rd, Mumbai 400017, Maharashtra, India Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, 1515 Ave 24-A, BR-13506900 Rio Claro, SP, Brazil Kumaun Univ, Dept Geol, Naini Tal 263002, India Banaras Hindu Univ, Dept Geol, Varanasi 221005, Uttar Pradesh, India Xiamen Univ, Dept Geol Oceanog, Xiamen 361102, Fujian, Peoples R China Xiamen Univ, State Key Lab Marine Environm Sci, Xiamen 361102, Fujian, Peoples R China Hokkaido Univ, Grad Sch Environm Sci, Kita Ku, N10W5, Sapporo, Hokkaido 0600810, Japan Scripps Inst Oceanog, 9500 Gilman Dr, La Jolla, CA 92093 USA Chinese Acad Sci, Inst Oceanol, Key Lab Marine Geol & Environm, 7 Nanhai Rd, Qingdao 266071, Shandong, Peoples R China Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, 1515 Ave 24-A, BR-13506900 Rio Claro, SP, Brazil National Centre for Polar and Ocean Research (NCPOR): 90/2018 National Research Foundation of Korea: 2016R1A2B4008256 National Research Foundation of Korea: 2019R1A2C1007701

International audience; Chemical weathering of silicate rocks on continents is thought to have played an important role in the evolution of past atmospheric carbon dioxide over geologic timescales. However, the detailed links between continental weathering and climate change over shorter timescales, and their potential impact on sediment records deposited in the ocean, remain poorly understood. Here, we present clay mineralogy and strontium-neodymium isotopic data for marine sediment records from the Northern Indian Ocean, with the aim of investigating the weathering response of large Himalayan river basins to orbital and millennial climate forcing. We show that past glaciated episodes of the late Quaternary corresponded to periods of increased physical erosion, associated with the preferential export of illite and chlorite assemblages from the Himalayan highlands having relatively radiogenic Sr isotopic signatures. In contrast, the warm periods of enhanced monsoon rainfall coincided with the transport of intensively weathered smectite-dominated soils derived from the floodplains, characterized by lower 87 Sr/ 86 Sr signatures. This finding suggests that the short-term climatic variability over late Quaternary timescales was accompanied by concomitant changes between high mountain-versus floodplain-dominated weathering regimes, with possible impact on the nature of weathered rocks and, as a consequence, on the carbon cycle.

Benthic foraminiferal assemblages and geochemical tracers (delta O-18, delta C-13 and C-14) have been analyzed on benthic and planktonic foraminifera from core MD77-176, located in the northern Bay of Bengal, in order to reconstruct the evolution of intermediate circulation in the northern Indian Ocean since the last glaciation. Results indicate that during the Last Glacial Maximum (LGM), Southern Sourced Water masses were dominant at the core site. A high relative abundance of intermediate and deep infaunal species during the LGM reflects low oxygen concentration and/or mesotropic to eutrophic deep water conditions, associated with depleted benthic delta C-13 values. During the Holocene, benthic foraminiferal assemblages indicate an oligotropic to mesotrophic environment with well-ventilated bottom water conditions compared with LGM. Higher values for benthic foraminifera delta C-13 and B-P C-14 age offsets suggest an increased contribution of North Atlantic Deep Water to the northern Bay of Bengal during the Late Holocene compared to the LGM. Millennial-scale events punctuated the last deglaciation, with a shift in the delta C-13 and the epsilon(Nd) values coincident with low B-P C-14 age offsets, providing strong evidence for an increased contribution of Antarctic Intermediate Water at the studied site. This was associated with enhanced upwelling in the Southern Ocean, reflecting a strong sea-atmospheric CO2 exchange through Southern Ocean ventilation during the last deglaciation.

Both the East Asian winter monsoon (EAWM) and El Nino (EN) activities are vital climate modes that regulate the Pacific hydrologic cycle. However, the Holocene interactions among the EAWM, EN activities, and tropical Pacific precipitation remain unclear due to the lack of appropriate EAWM proxies. Here, we present high-resolution grain size records from the East China Sea shelf along with a transient climate model simulation to study the Holocene EAWM evolution and compare the findings with paleo-EN precipitation-related proxies records. The millennial-scale oscillations of grain size records, which are indicative of the intensity of the EAWM-driven coastal current, reveal an anti-phase coupling between the EAWM and EN-related tropical Pacific precipitation on a millennial timescale since 5.8 ka. These results, which are consistent with simulation results, indicate that the intensified EAWM could not only reduce equatorial western Pacific precipitation by reducing the sea surface temperature but also likely change boundary conditions in the tropical Pacific (i.e., the east-west Pacific temperature gradient and westerly anomaly) to favor the formation of subsequent intensive EN activities. The enhanced EN activities, inferred by the positive tropical eastern Pacific precipitation anomalies, could subsequently suppress the EAWM through anomalous low-level anticyclones and associated southerly anomalies, thereby generating intensified tropical western Pacific (mainly tropical monsoon areas) precipitation. Our study highlights these intrinsic interactions during the mid- to late Holocene and has useful implications for understanding this millennial-scale climate oscillation, which may represent periodic atmospheric exchange between high- and low-latitude climate systems by mediating the EAWM.

International audience; Reconstructing the Cenozoic sedimentary history of the Bay of Bengal (BoB) is significant for understanding the evolutionary history of South Asian river systems and the links between river development, tectonic deformation and global climate change. Here, we present the first long-term clay mineral record combined with Sr-Nd isotopic compositions from a 200-m-long sediment core from Ocean Drilling Program (ODP) Site 758 in the southern BoB to establish past variations in sediment sources and river evolution that have occurred since the late Eocene. Provenance analysis suggests that the contribution of the Himalayan source materials from the Irrawaddy and Brahmaputra Rivers to the study site became more important and stable since 22 Ma and 8 Ma, respectively. This new evidence indicates that the Brahmaputra and Irrawaddy Rivers were possibly initiated in the early Miocene (~22 Ma). Considering the timing of major tectonic and climatic evolution in South Asia, we conclude that the two phases of tectonic uplift of the Himalayan orogen that occurred in the early and late Miocene were the primary controls on river development in South Asia and provenance changes in the southern BoB. Global cooling and Indian drying after the late Miocene could also have strengthened Himalayan erosion and contributed more illite and chlorite to the South Asian margin.

Clay mineralogical analysis and scanning electron microscope (SEM) analysis were performed on deep-sea sediments cored on the Benham Rise (core MD06-3050) in order to reconstruct long-term evolution of East Asian Summer Monsoon (EASM) rainfall in the period since 2.36 Ma. Clay mineralogical variations are due to changes in the ratios of smectite, which derive from weathering of volcanic rocks in Luzon Island during intervals of intensive monsoon rainfall, and illite- and chlorite-rich dusts, which are transported from East Asia by winds associated with the East Asian Winter Monsoon (EAWM). Since Luzon is the main source of smectite to the Benham Rise, long-term consistent variations in the smectite/(illite + chlorite) ratio in core MD06-3050 as well as ODP site 1146 in the Northern South China Sea suggest that minor contributions of eolian dust played a role in the variability of this mineralogical ratio and indicate strengthening EASM precipitation in SE Asia during time intervals from 2360 to 1900 kyr, 1200 to 600 kyr, and after 200 kyr. The EASM rainfall record displays a 30 kyr periodicity suggesting the influence of El Nino–Southern Oscillation (ENSO). These intervals of rainfall intensification on Luzon Island are coeval with a reduction in precipitation over central China and an increase in zonal SST gradient in the equatorial Pacific Ocean, implying a reinforcement of La Nina-like conditions. In contrast, periods of reduced rainfall on Luzon Island are associated with higher precipitation in central China and a weakening zonal SST gradient in the equatorial Pacific Ocean, thereby suggesting the development of dominant El Nino-like conditions. Our study, therefore, highlights for the first time a long-term temporal and spatial co-evolution of monsoonal precipitation in East Asia and of the tropical Pacific ENSO system over the past 2.36 Ma.

The two-stage increase in atmospheric carbon dioxide (CO2), and the associated decrease in radiocarbon (14C) during the last deglaciation, are thought to have been linked to enhanced Southern Ocean upwelling and the rapid release of sequestered 14C-depleted CO2. Antarctic Intermediate Water (AAIW), originating from the Southern Ocean, reflects variations in the Southern Ocean and, crucially, mirrors the chemical signature of upwelling deep water. However, the penetration of AAIW into the Northern Indian Ocean and its relationship with deglacial climate changes have not been thoroughly elucidated to date. Here, we present the neodymium isotopic composition ( e Nd ) of mixed planktonic foraminifera from core MD77-176 from an intermediate depth in the Northern Indian Ocean to reconstruct the past evolution of intermediate water during deglaciation. The e Nd record in the Northern Indian Ocean displays two pulse-like shifts towards more radiogenic Southern Ocean values during the deglaciation, and these shifts coincide with excursions in Δ 14 C and e Nd records in the Pacific and Atlantic Oceans. These results suggest invasion of AAIW into the Northern Hemisphere oceans associated with enhanced Southern Ocean ventilation during deglaciation. Our new e Nd record strongly supports the close linkage of AAIW propagation and atmospheric CO2 rise through Southern Ocean ventilation during deglaciation.

International audience; El Niño/Southern Oscillation (ENSO) activity and the Pacific Walker Circulation are controlled by the zonal sea surface temperature (SST) gradient between the western and Eastern Equatorial Pacific (EEP) and the corresponding barometric difference. Variations in the zonal SST gradient since the early Pleistocene have primarily been triggered by changes in the SST in the Eastern Equatorial Pacific. However, the response of the ENSO‐like long‐term state to the cooling of the EEP and its coupling role with tropical Pacific climate changes are still not well established. Here we present a high‐resolution grain‐size record spanning the last 2.36 Myr, obtained from marine core sediment located in the West Philippine Sea in order to decipher the tropical pacific climate changes and reveal its controlling mechanism. By combining our data with other long‐term climatic records from the Equatorial Pacific, we demonstrate that the cooling of SST and enhanced upwelling in the EEP resulted in the development of the Walker Circulation and increased monsoon precipitation in Luzon from 2.2 to 1.6 Myr, from 1.2 to 0.8 Myr, and since 0.2 Myr ago. The progressive cooling of the high‐latitudes in the Quaternary may be responsible for our observation here. A newly identified 100 kyr dominant period between 2.2 and 1.6 Myr in the ENSO‐like modulated Pacific climate records indicates that the ENSO‐like system may play a key role in facilitating or responding to the global climate changes.

Heavy metal concentrations in 36 samples of surface sediments from Hainan Island rivers were determined to evaluate the level of contamination in the region. Heavy metal concentrations (mg/kg) of Hainan Island rivers were in the range of 0.01-0.58 mg/kg for Hg, 0.09-0.70 mg/kg for Cd, 1.80-36.87 mg/kg for As, 15.33-69.32 mg/kg for Pb, 4.46-150.89 mg/kg for Cu, 6.64-104.95 mg/kg for Cr and 22.11-199.11 mg/kg for Zn. Contamination indices including contamination factor, enrichment factor, and geoaccumulation index, and multivariate statistical analyses indicated that Wenlan River was relatively at a considerable pollution level; Nandu, Changhua, Lingshui, Wanquan and Zhubi rivers were at a low-to-moderate pollution level; Beimen and Ningyuan rivers were at a level of relatively low pollution. Principal component analysis indicated that Cd, Pb, Cr and Zn were predominantly sourced from anthropogenic sources; whereas, Cu, As and Hg were from lithogenic sources. This study would be helpful for sustainable land use and marine management in the region.

主要对白令海南部IODP U1340井位上新世以来(~4.3 Ma)的粘土矿物组合和结晶学特征进行了分析, 探讨了研究井位中粘土矿物的物质来源及其记录的古气候变化历史. 结果表明, U1340井位中的粘土矿物组合以伊利石占绝对优势(平均含量为70%), 蒙脱石和绿泥石次之(平均含量分别为17%和10%), 高岭石含量很低(平均含量3%). 研究井位中粘土矿物组合及其物源区主要受气候特征的影响, 在温暖气候时期(如9.21 ka以来)主要来自邻近的阿留申岛弧, 蒙脱石含量较高; 而冷气候时期(如2.74~1.07 Ma)主要源自阿拉斯加大陆, 伊利石和绿泥石含量升高. 利用蒙脱石/(伊利石+绿泥石)比值及伊利石和蒙脱石的结晶学特征较好地揭示了白令海南部的古气候变化历史: 白令海南部在4.3~3.94 Ma以暖湿气候为主, 3.94~3.6 Ma则主要受到干冷气候的控制, 同时阿留申岛弧火山作用在这一时期加强; 此后逐渐向冷湿气候转变, 至2.74 Ma受北半球冰川作用的影响气候再次呈现干冷的特征; 1.95 Ma开始逐渐向冷湿气候过渡, 经历1.07~0.8 Ma中更新世气候转型之后, 白令海南部主要受控于冷湿气候, 但在~0.42 Ma(MIS 11), ~0.33 Ma(MIS 9)及~0.12 Ma(MIS 5), 气候相对温暖, 化学风化作用加强; ~9.21 ka全新世以来白令海南部以相对的暖湿气候为主.

Clay mineral assemblages and crystallinities in sediments from IODP Site 1340 in the Bering Sea were analyzed in order to trace sediment sources and reconstruct the paleoclimatic history of the Bering Sea since Pliocene (the last ∼4.3 Myr). The results show that clay minerals at Site U1340 are dominated by illite, with a moderate amount of smectite and chlorite, and minor kaolinite. Sediment source studies suggest that the clay mineral assemblages and their sources in the studied core are controlled primarily by the climate conditions. During the warm periods, clay minerals originated mainly from the adjacent Aleutian Islands, and smectite/(illite+chlorite) ratios increased. During the cold periods, clay minerals were derived primarily from the Alaskan region, and smectite/(illite+chlorite) ratios decreased. Based on smectite/(illite+chlorite) ratios and clay mineral crystallinities, the evolutionary history of the paleoclimate was revealed in the Bering Sea. In general, the Bering Sea was characterized by warm and wet climate condition from 4.3 to 3.94 Myr, and then cold and dry condition associated with the enhanced volcanism from 3.94 to 3.6 Myr. Thereafter, the climate gradually became cold and wet, and then was dominated by a cold and dry condition since 2.74 Myr, probably induced by the intensification of the Northern Hemisphere Glaciation. The interval from 1.95 to 1.07 Myr was a transitional period of the climate gradually becoming cold and wet. After the middle Pleistocene transition (1.07 to 0.8 Myr), the Bering Sea was governed mainly by cold and wet climate with several intervals of warm climate at ∼0.42 Ma (MIS 11), ∼0.33 Ma (MIS 9) and ∼0.12 Ma (MIS 5), respectively. During the last 9.21 kyr (the Holocene), the Bering Sea was characterized primarily by relatively warm and wet climatic conditions.

Constraining the dissolved neodymium (Nd) cycle in the ocean is paramount for using Nd isotopic composition ( e Nd ) as a tracer to reconstruct deep-sea paleocirculations or continental weathering on different time scales. Dissolved eNd has been measured in seawater samples from six hydrological stations collected along ∼89°E North–South transect in the Bay of Bengal (BoB) in order to assess the impact of seasonal freshwater and sediment discharges from the continental river systems. Seawater samples collected in this study during June 2012 reveal more radiogenic eNd (a difference of ∼2 Epsilon units for the upper 2000 m, and ∼0.5 Epsilon unit below 2000 m) and ∼3–8 pmol/kg lower Nd concentrations than the reported values of nearby seawater samples collected in November 2008. These observations are most plausibly explained by a seasonal variations in dissolved Nd concentrations and eNd in the BoB, induced by seasonal variations in the freshwater and sediment discharges from the Ganges–Brahmaputra (G–B) river system. However, we cannot entirely exclude the possibility of spatial differences given that the water stations collected in this study are not exactly the same positions collected in November 2008. A two-box model suggests, (1) the particulate Nd inputs from the G–B river system mainly control the seasonal shift of eNd observed in the BoB seawater, and (2) a very rapid Nd exchange exists between lithogenic particles and seawater (at least on the scale of a few months). Seasonal changes in seawater eNd may also occur in other marginal seas and in the outflows of major rivers, and these need to be taken into account when using the eNd proxy in the ocean.

High-resolution multi-proxy records, including clay minerals and Sr-Nd-Pb isotopes of the clay-sized silicate fraction of sediments from IODP Site U1429 in the northern Okinawa Trough, provide reliable evidence for distinct control mechanism on fine-grained sediments input from the Yellow River and the southern Japanese Islands to the northern Okinawa Trough since 34 ka BP. Provenance analysis indicates that the sediments were mainly derived from the Yellow River and the island of Kyushu. Since the last glacial, clay-sized sediments transported from the Yellow River to the study site were strongly influenced by sea-level fluctuation. During low sea-level stage (∼34‒14 ka BP), the paleo-Yellow River mouth was positioned closer to the northern Okinawa Trough, favoring large fluvial discharge or even direct input of detrital sediments, which resulted about four times more flux of clay-sized sediments supply to the study area as during the relatively high sea-level stage (∼14‒0 ka BP). The input of Kyushu-derived clay-sized sediments to the study site was mainly controlled by the Kuroshio Current and Tsushima Warm Current intensity, with increased input in phase with weakened Kuroshio Current/Tsushima Warm Current. Our study suggests that the Kuroshio Current was very likely flowed into the Okinawa Trough and thus influenced the fine-grained sediment transport in the area throughout the last glacial and deglacial. During ∼34‒11 ka BP, the Kyushu clay-sized sediment input was mainly controlled by the Kuroshio Current. Since ∼11 ka BP, the occurrence of Tsushima Warm Current became important in influencing the Kyushu fine-grained sediment input to the northern Okinawa Trough.

Made available in DSpace on 2022-04-28T19:05:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-02-21 In the Arabian Sea, South Asian monsoon (SAM)-induced high surface water productivity coupled with poor ventilation of intermediate water results in strong denitrification within the oxygen minimum zone (OMZ). Despite the significance of denitrification in the Arabian Sea, we have no long-term record of its evolution spanning the past several million years. Here, we present the first record of denitrification evolution since Late Miocene (∼10.2 Ma) in the Eastern Arabian Sea, where the SAM generates moderate surface water productivity, based on the samples retrieved during the International Ocean Discovery Program (IODP) Expedition 355. We find that (i) the SAM was persistently weaker from ∼10.2 to 3.1 Ma; it did not intensify at ∼8 Ma in contrast to a few previous studies, (ii) on tectonic timescale, both the SAM and the East Asian Monsoon (EAM) varied synchronously, (iii) the first evidence of denitrification and productivity/SAM intensification was at ∼3.2-2.8 Ma that coincided with Mid-Pliocene Warm Period (MPWP), and (iv) the modern strength of the OMZ where denitrification is a permanent feature was attained at ∼1.0 Ma. National Centre for Antarctic and Ocean Research Department of Oceanography Pusan National University Department of Geology and Geophysics Louisiana State University, E253 Howe-Russell-Kniffen, Geoscience Complex International Ocean Discovery Program Texas A&M University, 1000 Discovery Drive College Department of Earth and Environmental Sciences University of Milano Bicocca, Piazza della Scienza 4 School of Geography Earth and Environmental Sciences University of Birmingham, Edgbaston Department of Earth and Planetary Sciences Faculty of Science and Engineering Macquarie University Level 2, The Australian Hearing Hub, 16 University Avenue Department of Earth and Environmental Sciences University of Texas at Arlington, Geosciences Building, 500 Yates Street Manipal Centre for Natural Sciences Manipal University, Dr. T.M.A. Pai Planetarium Building MARUM University of Bremen, Leobener Strasse Center for Advanced Marine Core Research/Natural Science Cluster Kochi University, 2-5-1 Akebono-cho Wadia Institute of Himalayan Geology, 33 GMS Road Marine Biotechnology Department National Institute of Ocean Technology, Velachery-Tambaram Main Road Department of Earth Sciences University of Southern California, 3651 Trousdale Parkway School of Geographical and Oceanographical Sciences Nanjing University, 163 Xianlin Avenue College of Earth Ocean and Atmospheric Sciences Oregon State University, 104 CEOAS Administration Building Geosciences Division National Centre for Earth Science Studies University College London, Gower Street Geological Oceanography Division National Institute of Oceanography ONGC 11 High, Bandra-Sion Link Road Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista, 1515 Avenida 24-A Department of Geology Kumaun University Department of Geology Banaras Hindu University Department of Geological Oceanography College of Ocean and Earth Sciences Xiamen University, Xiping Building, Xiang'an South Road Graduate School of Environmental Science Hokkaido University, N10W5, Kita-ku Scripps Institution of Oceanography, 9500 Gilman Drive Key Laboratory of Marine Geology and Environment Institute of Oceanology Chinese Academy of Sciences, 7 Nanhai Road Laboratoire Géosciences Paris-Sud (GEOPS UMR8148-CNRS) Université de Paris-Sud (Orsay), Bâtiment 504 Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista, 1515 Avenida 24-A

International audience; Atmospheric CO2 and global climate are closely coupled. Since 800 ka CO2 concentrations have been up to 50% higher during interglacial compared to glacial periods. Because of its dependence on temperature, humidity, and erosion rates, chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition. Cooler and drier conditions and lower non-glacial erosion rates suppressed in situ chemical weathering rates during glacial periods. However, using systematic variations in major element geochemistry, Sr–Nd isotopes and clay mineral records from Ocean Drilling Program Sites 1143 and 1144 in the South China Sea spanning the last 1.1 Ma, we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials. We attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands. Our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for ∼9% of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial–interglacial variation of ∼80 ppmv. As a result, if similar magnitudes can be identified in other tropical shelf-slope systems, the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric CO2 during cold stages of the Quaternary. This in turn would have caused an intensification of glacial cycles.

The eolian component in Pacific Ocean sediments has been recognized as providing a direct link between the continental loess and marine delta O-18 climate records over orbital timescales since 500 ka. Here we extend this eolian record over the past one million years. We constructed high-resolution clay mineral stratigraphies based on delta O-18 chronology in sediments from the International Marine Past Global Change (IMAGES) Core MD06-3050 from the West Philippine Sea in order to trace the sources of clay minerals and reconstruct proxy records of past changes in the Asian eolian input to the basin since 1.0 Ma. The clay mineral assemblage in Core MD06-3050 mainly consists of smectite (similar to 65%) and illite (similar to 25%), with minor kaolinite (similar to 5%) and chlorite (similar to 5%). Provenance analysis suggests that smectite was derived mainly from the weathering of volcanic rocks on Luzon island, whereas illite, chlorite and kaolinite were mainly transported as eolian dust by the East Asian winter monsoon from central Asia. Illite/smectite values in Core MD06-3050 are generally higher and more variable during glacial periods and lower during interglacials, suggesting that higher eolian input to the West Philippine Sea generally co-varied with East Asian winter monsoon intensity and more aridity in continental Asia since 1.0 Ma. Spectral analysis further reveals the close link between the extent of high-latitude glaciation, East Asian winter monsoon intensity and eolian input to the West Philippine Sea at eccentricity (100 ka), obliquity (41 ka) and precession (23 ka) bands since 1.0 Ma. (C) 2012 Elsevier B.V. All rights reserved.