Rates and fluxes of centennial-scale carbon storage in the fine-grained sediments from the central South Yellow Sea and Min-Zhe belt, East China Sea

The global carbon cycle has played a key role in mitigating global warming and climate change.Long-term natural and anthropogenic processes influence the composition,sources,burial rates,and fluxes of carbon in sediments on the continental shelf of China.In this study,the rates,fluxes,and amounts of carbon storage at the centennial scale were estimated and demonstrated using the case study of three fine-grained sediment cores from the central South Yellow Sea area(SYSA) and Min-Zhe belt(MZB),East China Sea.Based on the high-resolution temporal sequences of total carbon(TC)and total organic carbon(TOC)contents,we reconstructed the annual variations of historical marine carbon storage,and explored the influence of terrestrial and marine sources on carbon burial at the centennial scale.The estimated TC storage over 100 years was 1.18×10~8 t in the SYSA and 1.45×10~9 t in the MZB.The corrected TOC storage fluxes at the centennial scale ranged from 17 to 28 t/(km^2·a)in the SYSA and from 56 to 148 t/(km^2·a)in the MZB.The decrease of terrestrial materials and the increase of marine primary production suggest that the TOC buried in the sediments in the SYSA and MZB was mainly derived from the marine autogenetic source.In the MZB,two depletion events occurred in TC and TOC storage from 1985 to 1987 and 2003 to 2006,which were coeval with the water impoundment in the Gezhouba and Three Gorges dams,respectively.The high-resolution records of the carbon storage rates and fluxes in the SYSA and MZB reflect the synchronous responses to human activities and provide an important reference for assessing the carbon sequestration capacity of the marginal seas of China.

Centennial-scale monsoon collapses during Marine Isotope Stage(MIS)7e detected in a northern Chinese stalagmite record

Occurrence or absence of centennial-scale climatic variability during Marine Isotope Stage(MIS)7e,the first peak interval of the Penultimate Interglacial,remains ambiguous due to the limited available high-resolved records.Here,we present a decadal-resolved stalagmiteδ^(18)O record from northern China spanning from 242.3 to 236.8 ka BP,covering MIS7e.The composite KLSδ^(18)O record,integrating this study with the previous record in the same cave,shows a descending trend from TerminationⅢto MIS7e,which follows the increasing Northern Hemisphere summer insolation(NHSI).This observation further emphasizes the important influence of NHSI on the glacial/interglacial transition.There are more large-amplitude,millennial-to centennial-scale variability occurring during TerminationⅢcompared with MIS7e,implying that ice-sheet decay potentially plays an important role in climatic excursions.Four centennial-scale summer monsoon collapses,peaking at~242.1,~240.8,~239.3 and~238.2 ka BP,are detected in our new record,indicating the pervasiveness of the intra-interglacial climatic instability.Given the lack of solar activity and freshwater outbursts data during MIS7e,it is not possible to conclude about the drivers of the identified abrupt climatic anomalous.Following the dynamic mechanisms of sub-millennial climatic anomalous during early Holocene,we tentatively propose that slowdown of the meridional overturning circulation caused by freshwater fluxes into North Atlantic and/or attenuated solar irradiance is the potential forcing for the abrupt climate events within MIS7e.Additionally,attenuated solar irradiance could also result in climatic anomalies through low-latitude processes.

Simulation of Centennial-Scale Drought Events over Eastern China during the Past 1500 Years

The characteristics and causes of centennial-scale drought events over eastern China during the past 1500 years were explored based on simulations of the Community Earth System Model （CESM）. The results show that centenni- al-scale drought events over eastern China occurred during the periods of 622-735 （Drought period 1, D1） and 1420-1516 （Drought period 2, D2） over the past 1500 years, which is comparable with climate proxy data. In D1, the drought center occurred in northern China and the Yangtze River valley; however, in southern China, precipitation was much more than usual. In D2, decreased precipitation was found across almost the whole region of eastern China. The direct cause of these two drought events was the weakened East Asian summer monsoon, and the specif- ic process was closely linked to the air-sea interaction of the Indo-Pacific Ocean. In DI, regions of maximum cool- ing were observed over the western Pacific, which may have led to anomalous subsidence, weakening the Walker cir- culation, and reducing the northward transport of water vapor. Additionally, upward motion occurred over southern China, strengthening convection and increasing precipitation. In D2, owing to the decrease in the SST, subsidence dominated the North Indian Ocean, blocking the low-level cross-equatorial flow, enhancing the tropical westerly an- omalies, and reducing the northward transport of moisture. Additionally, descending motion appeared in eastern China, subsequently decreasing the precipitation over the whole region of eastern China. The anomalous cooling of the Indo-Pacific Ocean SST may have been caused by the persistently low solar irradiation in D1; whereas, in D2, this characteristic may have been influenced not only by persistently low solar irradiation, but frequent volcanic erup- tions too.

Effect of farmland expansion on drought over the past century in Songnen Plain,Northeast China

The effects of human activities on climate change are a significant area of research in the field of global environmental change.Land use and land cover change(LUCC)has a greater effect on climate than greenhouse gases,and the effect of farmland expansion on regional drought is particularly important.From the 1910s to the 2010s,cultivated land in Songnen Plain increased by 2.67 times,the area of cultivated land increased from 4.92×10^4 km^2 to 13.14×10^4 km^2,and its percentage of all land increased from 25%to 70%.This provides an opportunity to study the effects of the conversion of natural grassland to farmland on climate.In this study,the drought indices in Songnen Plain were evaluated from the 1910s to the 2010s,and the effect of farmland expansion on drought was investigated using statistical methods and the Weather Research and Forecasting Model based on UK’s Climatic Research Unit data.The resulting dryness index,Palmer drought severity index,and standardized precipitation index values indicated a significant drying trend in the study area from 1981 to 2010.This trend can be attributed to increases in maximum temperature and diurnal temperature range,which increased the degree of drought.Based on statistical analysis and simulation,the maximum temperature,diurnal temperature range,and sensible heat flux increased during the growing season in Songnen Plain over the past 100 years,while the minimum temperature and latent heat flux decreased.The findings indicate that farmland expansion caused a drying trend in Songnen Plain during the study period.