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AbstractAs the largest submarine fan, the Bay of Bengal (BoB) captures the abundant environment and climate fingerprints on different time scales. To investigate the sedimentary response to climate change since the Last Glacial Maximum (LGM), an integrated survey was performed to study grain size, major, and trace elements (Al2O3, CaO, K2O, Na2O, TiO2, Sr, and Rb) of core BoB-24 sediments from the central BoB. The (K/Al)-TiO2 (%) relationship of the sediments was taken for the discrimination of provenance, which indicated that sediments from core BoB-24 in 24~6.5 cal ka BP were primarily from terrigenous material input from the Himalayas. In contrast, the material contribution from the Indian subcontinent increased distinctly since 6.5 cal ka BP. The rising sea level severed direct material supply, thus causing the evolution of sediment provenance of the central BoB. Meanwhile, the strengthened Indian summer monsoon (ISM) in the Holocene affected detrital material transport from offshore to the central BoB. After understanding the sediment provenance in the study, we choose the sensitive grain-size fraction to show the evolution of hydrodynamic conditions. The chemical index of alteration (CIA) and Ti/Ca and Rb/Sr ratios are calculated to indicate the change in terrigenous input and weathering intensity. The contents of sediment fraction from 11.05 to 15.63 μm, CIA, and ratios of Ti/Ca and Rb/Sr in core BoB-24 showed the same trends, which were low during the last deglaciation and late Holocene but high in the Early Holocene. The trends were strongly correlated with the variation of the Indian summer monsoon, indicating the possible impact of Indian monsoon on sediment transport in the Bay of Bengal. Alternative indicators such as the contents of ratios of Ti/Ca and Rb/Sr, CIA, and sensitive grain-size content in sediments of core BoB-24 jointly record the evolution history of ISM since 24 ka BP in the Bay of Bengal. Although the sensitivity and response of each indicator to the paleoenvironment and paleoclimate change are slightly different, on the whole, the change trend is the same. Specifically, four warm-cold alternating periods (Heinrich Event 1, Bølling/Allerød, Younger Dryas, and Early Holocene Climatic Optimum) had a strong signal in these proxies that indicated that the millennial-scale climate controls the terrigenous input to the Bay of Bengal, where a high value occurs in warm events and low value in cold events. The sedimentary pattern of the northeastern Indian Ocean provides scientific evidence for an insight into the regional response to global climate change and the long-term climate change trend of the human environment across the monsoon region.

AbstractThe mineralogical and geochemical compositions of the sediments deposited by rivers have been used extensively to evaluate past chemical weathering and the physical erosion history of drainage basins at different time scales. However, the role of sediment sorting in the mineralogical and geochemical compositions of river sediment needs to be better constrained because it could significantly modify proxies used to evaluate weathering intensity in the past. In this study, major and trace element concentrations and mineralogical compositions were determined on seven different grain-size fractions of riverbed samples taken from the Pahang and Kelantan Rivers in the Malay Peninsula. The main aims are to assess chemical weathering and the fractionation of alkali elements during sediment transportation under tropical climate conditions. Fine sediments (from

AbstractRadon (222Rn) has been widely employed as a tracer for estimating submarine groundwater discharge (SGD). However, the uncertainty of the SGD estimation remains significant, due to the spatial variability of radon in groundwater. In this study, we analyzed the hydrochemical proprieties of seawater and coastal groundwater in the Upper Gulf of Thailand and discussed the distribution characteristics of 222Rn in aquifers in terms of aquifer lithology, groundwater system recharge conditions, and water retention time. The results suggested that the residence time of groundwater and the process of groundwater salinization have the greatest impact on the distribution of 222Rn activity. A 222Rn mass balance model, synthesizing the distribution characteristics of 222Rn in groundwater and tidal influences on SGD, was built to estimate the submarine groundwater discharge in the Upper Gulf of Thailand. The result showed that the SGD flux of the Upper Gulf of Thailand was 0.0203 m/d. Moreover, there is a positive correlation between tidal height and the activity of 222Rn in groundwater. The SGD observed during the low tide was about 1.25 times higher than that observed during the high tide. This may influence the marine geochemical cycles of elements and their impact on marine ecosystems.

AbstractThe Sea of Japan (JS), a unique marginal sea without any large river influxes in the western Pacific, provides ample information about the evolution of sea level, East Asian monsoons (EAM), sea ice activity, and ocean currents in geological time. However, insufficient investigation in the western JS limits our knowledge of East Asian climate change. This study utilizes major and trace elements and Pb isotopes of fine siliciclastic components (

AbstractWildfire is an integral part of the Earth’s climate system and plays an important role in shaping terrestrial ecosystems and biodiversity, atmospheric chemistry, regional climate, and the carbon cycle in the Earth’s history. However, the lack of high-resolution records of long wildfires limits our understanding of the natural variability, long-term trends of wildfire activity, and the reasons behind the changes in wildfire on orbital timescales. Here, a 320 ka long high-resolution wildfire record from the subarctic North Pacific is reconstructed with black carbon (BC), including its two subtypes char and soot. A 7-day-long back trajectory simulation analysis reveals the higher frequency of trajectories comes from Siberia. Our data show that continuous incidence of wildfire on a continental scale over the last 320 ka was higher during glacial periods than during the interglacial periods. The increase in wildfire frequency during glacial periods is ascribed to less precipitation. Contrasting patterns of wildfire incidence between marine isotope stages 2 and 6 may be ascribed to different fuel availability, which is related to contrasting configurations of the Northern Hemisphere ice sheet between glacial periods. A significant periodicity of 23 ka of our wildfire record suggests the precession of the Earth’s orbit pace wildfire development. The tight coupling of intensified wildfire and enhanced nutrient utilization efficiency suggests a nontrivial role of fire in the climate system.

AbstractThe continental margin is one of the major depocenters for terrigenous sediments in the world ocean. Complex interactions between land and sea control the sedimentary processes along the continental margin. The Okinawa Trough (OT) receives huge amounts of terrigenous materials transported by rivers from the adjacent landmass, while the Kuroshio Current (KC) and the North Pacific Intermediate Water jointly play major roles in oceanic climate and regional deposition patterns of terrigenous sediments. Various studies have investigated the changes in terrigenous sediment provenance in the central OT only since the last glacial. Still, few studies focus on more long-term variations in terrigenous deposition over the last few glacial-interglacial cycles. Here, we report a new high-resolution sediment geochemistry record of a well-dated core MD01-2404 taken from the central OT covering a timespan of 92 kyr. Our results show dynamic glacial-interglacial changes in sediment compositions and terrigenous deposition patterns. Bulk sediments in MD01-2404 comprise relatively high biogenic components during interglacials, while higher terrigenous fractions during the last deglacial and glacial periods. We suggest that the provenance of terrigenous sediments is mainly derived from Taiwanese rivers, Yangtze River, and Yellow River with hydrothermal inputs. During the time interval of 37 to 46 kyr, a new finding of “Negative Ce Anomaly Event” in the central OT firstly reported here is attributed to a combination of suboxic conditions in deep and pore waters and the addition of depleted Ce-bearing sediments. Temporal changes of deposition patterns in the central OT are attributed to complex interactions among dynamic glacial-interglacial changes in eustatic sea level, the East Asian summer monsoon, and the KC.