East Asian Continent Research Articles

Pre‐Pleistocene geological events shaping diversification and distribution of primitively segmented spiders on East Asian margins

AbstractAimPhylogeographical research in the East Asian continent and islands (East Asian Margins, or EAM) suggests predominant Pleistocene over‐water dispersal events from continent to islands, but more ancient biogeographical patterns in EAM remain obscure. We explored biogeographical histories and population genetic structures of the primitively segmented spiders, Heptathela and Ryuthela (Liphistiidae), broadly codistributed across EAM islands. To test competing biogeographical hypotheses, we looked for geohistoric events that may have shaped their distributional patterns.LocationKyushu and Ryukyus.MethodsWe sampled 17 Heptathela and Ryuthela species on 10 out of 12 EAM islands and sequenced fragments of two mitochondrial and three nuclear genes. We performed phylogenetic, network, time‐calibrated and biogeographical analyses to identify lineages, estimate their divergence times, and reconstruct ancestral ranges. We also assessed genetic diversity and historic demography of each lineage.ResultsPhylogenetic origin of Heptathela + Ryuthela is estimated at 26.6–18.4 Ma (95% HPD) when EAM islands became separated from the continent. The crown ages of Heptathela (18.0–10.7 Ma) and Ryuthela (17.8–8.7 Ma) coincide with the formation of Japan Sea and Okinawa Trough respectively. A split within Ryuthela (13.9–6.0 Ma) coincides with the opening of the Kerama Gap, but a split within Heptathela (18.0–10.7 Ma) pre‐dates the formation of the Tokara Gap. Speciation within Heptathela and Ryuthela is relatively recent (6.0–0.3 Ma). Population genetic and demographic results suggest interrupted gene flow within and among islands, with most species exhibiting stable past populations.Main conclusionsHistoric biogeographical reconstructions strongly suggest predominant vicariant origins of EAM island liphistiids. Restricted gene flow following barrier formation is the dominant speciation force in these spiders. As they never seem to cross bodies of water, their past range expansion, successive fragmentation of EAM, and other vicariant events, must have shaped the detected genetic boundaries among and within islands.

A new conceptual model for quantifying transboundary contribution of atmospheric pollutants in the East Asian Pacific rim region

Transboundary transport of air pollution is a serious environmental concern as pollutant affects both human health and the environment. Many numerical approaches have been utilized to quantify the amounts of pollutants transported to receptor regions, based on emission inventories from possible source regions. However, sparse temporal–spatial observational data and uncertainty in emission inventories might make the transboundary transport contribution difficult to estimate. This study presents a conceptual quantitative approach that uses transport pathway classification in combination with curve fitting models to simulate an air pollutant concentration baseline for pollution background concentrations. This approach is used to investigate the transboundary transport contribution of atmospheric pollutants to a metropolitan area in the East Asian Pacific rim region. Trajectory analysis categorized pollution sources for the study area into three regions: East Asia, Southeast Asia, and Taiwan cities. The occurrence frequency and transboundary contribution results suggest the predominant source region is the East Asian continent. This study also presents an application to evaluate heavy pollution cases for health concerns. This new baseline construction model provides a useful tool for the study of the contribution of transboundary pollution delivered to receptors, especially for areas deficient in emission inventories and regulatory monitoring data for harmful air pollutants.

Geochemistry of river‐borne clays entering the East China Sea indicates two contrasting types of weathering and sediment transport processes

AbstractThe East China Sea is characterized by wide continental shelf receiving a huge input of terrigenous matter from both large rivers and mountainous rivers, which makes it an ideal natural laboratory for studying sediment source‐to‐sink transport processes. This paper presents mineralogical and geochemical data of the clays and bulk sediments from the rivers entering the East China Sea, aiming to investigate the general driving mechanism of silicate weathering and sediment transport processes in East Asian continental margin. Two types of river systems, tectonically stable continental rivers and tectonically active mountainous rivers, coexist in East Asia. As the direct weathering products, clays can better reflect the silicate weathering regimes within the two river systems. Provenance rock types are not the dominant factor causing silicate weathering intensity difference existed in the East Asian rivers. The silicate weathering intensity of tectonically stable river basins is primarily driven by monsoon climate, and the sediment transfer is relatively slow because of natural trapping process and increasing damming effect. The geochemistry of these river‐borne sediments can thus indicate paleo‐weathering intensities in East Asian continent. In contrast, silicate weathering intensity in tectonically active mountainous rivers is greatly limited by strong physical erosion despite the high temperature and highest monsoon rainfall. The factors controlling silicate weathering in tectonically active catchments are complex and thus, it should be prudent to use river sediment records to decipher paleoclimate change. These two different silicate weathering regimes and sediment transport processes are manifestations of the landscape evolution and overall dominate the sedimentation in Asian continental margin.

여름철 일본에 영향을 주는 태풍빈도의 감소추세

This study analyzed the climate regime shift using statistical change-point analysis on the time-series tropical cyclone (TC) frequency that affected Japan in July to September. The result showed that there was a significant change in 1995 and since then, it showed a trend of rapidly decreasing frequency. To determine the reason for this, differences between 1995 to 2012 (9512) period and 1978 to 1994 (7894) period were analayzed. First, regarding TC genesis, TCs during the 9512 period showed a characteristic of genesis from the southeast quadrant of the tropical and subtropical western North Pacific and TCs during the 7894 period showed their genesis from the northwest quadrant. Regarding a TC track, TCs in the 7894 period had a strong trend of moving from the far east sea of the Philippines via the East China Sea to the mid-latitude region in East Asia while TCs in the 9512 period showed a trend of moving from the Philippines toward the southern part of China westward. Thus, TC intensity in the 7894 period, which can absorb sufficient energy from the sea as they moved a long distance over the sea, was stronger than that of 9512. Large-scale environments were analyzed to determine the cause of such difference in TC activity occurred between two periods. During the 9512 period, anomalous cold and dry anticyclones were developed strongly in the East Asia continent. As a result, Korea and Japan were affected by the anomalous northerlies thereby preventing TCs in this period from moving toward the mid-latitude region in East Asia. Instead, anomalous easterlies (anomalous trade wind) were developed in the tropical western Pacific so that a high passage frequency from the Philippine to the south China region along the anomalous steering flows was revealed. The characteristics of the anomalous cold and dry anticyclone developed in the East Asia continent were also confirmed by the analysis of air temperature, relative humidity and sensible heat net flux showing that most regions in East Asia had negative values.

북태평양 스톰트랙 활동과 동아시아 겨울 몬순의 상관성에 관한 CMIP5 모델의 모의 성능

Based on the CMIP5 historical simulation datasets, we assessed the performance of state-of-the-art climate models in respect to the relationship between interannual variabilities of the North Pacific synoptic eddy (NPSE) and East Asian winter monsoon (EAWM). Observation (ERA-Interim) shows a high negative correlation (-0.73) between the interannual variabilities of East Asian winter monsoon (EAWM) intensity and North Pacific synoptic eddy (NPSE) activity during the period of 1979~2005. Namely, a stronger (weaker) EAWM is related to a weaker (stronger) synoptic eddy activities over the North Pacific. This strong reverse relationship can be well explained by latitudinal distributions of the surface temperature anomalies over East Asian continent, which leads the variation of local baroclinicity and significantly weakens the baroclinic wave activities over the northern latitudes of . This feature is supported by the distribution of the meridional heat flux () anomalies, which have negative (positive) values along the latitudes for strong(weak) EAWM years. In this study, the historical simulations by 11 CMIP5 climate models (BCC-CSM1.1, CanESM2, GFDL-ESM2G, GFDL-ESM2M, HadGEM2-AO, HadGEM2-CC, IPSL-CM5A-LR, MPI-ESM-LR, MPI-ESM-MR, MRI-CGCM3, and NorESM1-M) are analyzed for DJF of 1979~2005. Correlation coefficient between the two phenomena is -0.59, which is comparable to that of observation. Model-to-model variation in this relationship is relatively large as the range of correlation coefficient is between -0.76 (HadGEM2-CC and HadGEM2-AO) and -0.33 (MRI-CGCM3). But, these reverse relationships are shown in all models without any exception. We found that the multi-model ensemble is qualitatively similar to the observation in reasoning (that is, latitudinal distribution of surface temperature anomalies, variation of local baroclinicity and meridional heat flux by synoptic eddies) of the reverse relationship. However, the uncertainty for weak EAWM is much larger than strong EAWM. In conclusion, we suggest that CMIP5 models as an ensemble have a good performance in the simulation of EAWM, NPSE, and their relationship.

Northern East Asian low and its impact on the interannual variation of East Asian summer rainfall

The strength of the East Asian summer monsoon and associated rainfall has been linked to the western North Pacific subtropical high (WNPSH) and the lower-tropospheric low pressure system over continental East Asia (EA). In contrast to the large number of studies devoted to the WNPSH, little is known about the variability of the East Asian continental low. The present study delineates the East Asian continental low using 850-hPa geopotential height. Since the low is centered over northern EA (NEA), we refer to it as the NEA low (NEAL). We show that the intensity of the NEAL has large interannual variation, with a dominant period of 2–4 years. An enhanced NEAL exhibits a barotropic structure throughout the whole troposphere, which accelerates the summer-mean upper-tropospheric westerly jet and lower-tropospheric monsoon westerly to its south. We carefully identify the anomalous NEAL-induced rainfall anomalies by removal of the tropical heating effects. An enhanced NEAL not only increases rainfall locally in northern Northeast China, but also shifts the East Asian subtropical front northward, causing above-normal rainfall extending eastward from the Huai River valley across central-northern Japan and below-normal rainfall in South China. The northward shift of the East Asian subtropical front is attributed to the following processes without change in the WNPSH: an enhanced NEAL increases meridional pressure gradients and the monsoon westerly along the East Asian subtropical front, which in turn induces a cyclonic shear vorticity anomaly to its northern side. The associated Ekman pumping induces moisture flux convergence that shifts the East Asian subtropical front northward. In addition, the frequent occurrence of synoptic cut-off lows is found to be associated with an enhanced NEAL. Wave activity analysis indicates that the interannual intensity change of the NEAL is significantly associated with the extratropical Polar Eurasian teleconnection, in addition to the forcing of the tropical WNP heating.

Mid-Holocene and last glacial maximum changes in monsoon area and precipitation over China

Sixty-one climate models participating in the Paleoclimate Modeling Intercomparison Project phases one (PMIP1) to three (PMIP3) were first evaluated in terms of their ability to reproduce the present annual, summer (May-September), and winter (November-March) precipitation climatology of China. Changes in monsoon area (CMA), monsoon precipitation (CMP), and monsoon precipitation intensity (CMPI) over China were then investigated using the results of 26 and 16 reliable climate models for mid-Holocene (MH) and last glacial maximum (LGM), respectively. Results show that relative to the reference period, the MH CMA, CMP, and CMPI consistently increased in 26, 26, and 22 models, respectively, with averages of 10.7% for CMA, 18.7% for CMP, and 7.3% for CMPI. Those changes were collectively attributable to an orbitally induced decrease in summer meridional temperature gradient and increases in summer land-sea thermal contrast between the East Asian continent and adjacent oceans. The role of the dynamic ocean was limited. Model results are generally consistent with geologic records over the monsoon regions in China. At the LGM, the CMA and CMP decreased in 15 models and the CMPI weakened in all 16 models, with averages of -7.7%, -25.1%, and -14.3%, respectively. In response to LGM forcing, the increase in summer meridional temperature gradient and decreases in zonal and meridional land-sea thermal contrast were the underlying mechanisms, and interactive ocean had a suppression effect. The simulated changes agree qualitatively with most of the limited proxy data across the CMA.

Distribution of Ozone and Related Compounds in the Marine Boundary Layer of the Northern South China Sea in 2010

To investigate the characteristics of air pollutants transported from the Asian continental regions to the marine boundary layer of the northern South China Sea (SCS), we recorded the continuous measurements of meteorology, sea surface radiative budget, and ozone (O3) and related compounds in the marine boundary layer near Taiwan during 2010 cruises. For the marine field campaign investigation, the contaminated O3 and related compounds (e.g., NO2, NO, CO, CH4, and NMHC) have been eliminated from research vessel's exhaust by using various meteorological factors. The mean values of O3 and its major precursors (NO2, NO, and CO) were 25 ± 9.9, 3.2 ± 1.8, 2.9 ± 1.7, and 204 ± 54 ppb, respectively. A high O3 mixing ratio is related to extreme shortwave radiation, high air temperature, less precipitation, and low wind speed and specific humidity. The results indicated a higher ∆O3/∆CO ratio of 0.2 at sunset during the March 2010 cruise mainly due to a long-range transport of aged plumes (> 3 days) originating from the super-region of Asian continent and a lower ∆O3/∆CO ratio of 0.12 at midday, mostly associated with the proximity to local sources of fresh plumes (< 2 days) during April 2010 and July 2010 cruises. The O3 and related compounds mixing ratios over the ocean are affected by emission source, Asian monsoon, wind speed, gas deposition, gas solubility, the chemical enhancement factor, the frontal inversion and the boundary layer height. A clear bulge in the diurnal cycle was observed between early morning and late afternoon for NOx, CO, and O3. Moreover, 5-d backward trajectories and Southeast Asia surface wind fields suggested that the southward export of the air masses in spring originated from Mongolia and the East Asian continent.

Climate Change Projections over CORDEX East Asia Domain using Multi-RCMs

In this study, global climate change scenario by HadGEM2-AO is dynamically downscaled using 5 Regional Climate Models (RCMs) for the Coordinated Regional Downscaling Experiment (CORDEX) - East Asia. All RCMs with 50-km horizontal resolution are integrated for continuous 71 years (1979-2049). In the evaluation of historical runs, all models tend to overestimate precipitation over the subtropical western North Pacific. For the surface air temperature, all models have cold biases over the East Asian continent compared to the observation. In the future projections, all models show similar changes in precipitation such as increasing precipitation over the tropical oceans and slightly decreasing precipitation over the East China Sea. In the mid-latitudes, convective precipitation tends to increase due to the enhanced convective instability, while non-convective precipitation tends to decrease slightly due to the changes in subtropical high and monsoon circulation. For surface air temperature, the warming tendency over the entire domain is captured by all models and it is larger in high latitude regions. The warming temperature is related to the increase in longwave radiation, which leads to prominent increase in minimum surface air temperature.

Temperate forests in continental East Asia

In this editorial, we introduce a Special Feature focusing on various aspects of temperate forest vegetation on the East Asian mainland (China and Korea). The papers included in this Special Feature encompass a range of topics, including plot-based vegetation survey, analysis of vegetation change along broad-scale environmental gradients and dynamics of both successional and climax forests.

우리나라 광주에서의 4월 평균 강수량에 대한 장기변동성 분석

We found that, in 1984, there was a climate regime shift in April mean precipitation in Gwangju of Jeollanam-do province, Korea using a statistical change-point analysis. During the period of post-1984(1985-2013), the April mean precipitation in the years post-1984 showed a distinct decrease, compared to the pre-1984 period(1954-1984). This regime shift was also observed in China and Japan, excluding southern China. One of the major causes for the decreasing April mean precipitation during the recent three decades was the increased snow depth in the mid-latitude regions of continental East Asia. The increased snow depth resulted in strengthened cold and dry anticyclone anomaly over continental East Asia and a relatively weakened subtropical anticyclone anomaly over the western North Pacific. The anomalous synoptic conditious supported a continuation of the typical winter pressure pattern of 'high-West and low-East' over East Asia in April. The intensified northerly winds from this zonal pressure pattern anomaly played a significant role in restricting the northern movement of the subtropical anticyclone and there by preventing the inflow of warm and humid air into Korea.

Late Ordovician volcanism in Korea constrains the timing for breakup of Sino-Korean Craton from Gondwana

In the early Paleozoic the Sino-Korean Craton (SKC) and South China Craton (SCC) were situated along the margin of east Gondwana. The SKC was connected to core Gondwana by an epeiric sea which was the site for deposition of lower Paleozoic sequences of SKC. The SKC and SCC may have drifted away from core Gondwana sometime during the mid-Paleozoic and would have been outboard microcontinents in the late Paleozoic, until they collided to form the East Asian continent in the Triassic. The breakup of SCC from Gondwana was suggested to have taken place at ∼380Ma, while no reliable suggestions have hitherto been made for breakup of SKC from Gondwana. This study presents a convincing evidence for breakup of SKC from Gondwana, based on the recognition of Late Ordovician volcanism in Korea. New SHRIMP U–Pb zircon ages, 445.0±3.7Ma and 452.5±3.2Ma, are obtained from trachytic rocks of the Ongnyeobong Formation of Taebaeksan Basin in Korea which occupied the marginal part of the SKC in the early Paleozoic. This Late Ordovician volcanism along with previous records of Ordovician volcanic activities along the western margin of the SKC is interpreted indicating the development of an incipient oceanic ridge. The oceanic ridge uplifted the SKC including the epeiric sea, which subsequently resulted in terminating the early Paleozoic sedimentation of the epeiric sea. The paucity of lower Paleozoic volcanic rocks across much of the SKC however suggests that the oceanic ridge did not extend into the epeiric sea. Instead, spreading of oceanic ridge entailed dextral movement of associated transform faults, which may have played a major role in breakup of SKC from mainland Gondwana by the end of Ordovician.

Distribution of the Mesozoic in the continental margin basins of the South China Sea and its petroliferous significance

Abstract Based on 40 wells encountering the Mesozoic sedimentary rocks, 52 thousands kilometers of seismic profiles covering most parts of the South China Sea (SCS) and the latest collection of gravity and magnetic data, the distribution of the Mesozoic in the continental margin of South China Sea and the oil and gas exploration prospect are studied. The Mesozoic is distributed in three main areas in the SCS: (1) the area of eastern Pearl River Mouth Basin and Southwest Taiwan Basin, where the Mesozoic buried at 1–3 km deep and 2–8 km thick, is thickest in the Chaoshan Depression and east Dongsha Uplift, and there is a long axis gentle fold in the east of the Pearl River Mouth Basin; (2) Liyue-Palawan Basin area, where the Mesozoic, 2–4 km deep and 2–5 km thick, is thickest in the south depression of the Liyue Basin; (3) Zhongjiannan-Wan'an-western Nanwei Basin area, where the Mesozoic is 3–5 km deep and 2–3 km thick. According to the spatial location relationship between the Mesozoic distribution and deep faults, it is inferred that the Mesozoic distribution is controlled by the eastern Yangjiang-Yitong Shoal fault, Balabac fault and YueDong-Wan'an fault, and affected by the uneven base uplifting and block faulting caused by the Mesozoic Pacific plate subduction to the East Asian continent. The study on the distribution of residual Mesozoic strata, structural traps and source rocks concludes that there are two favorable areas for the Mesozoic hydrocarbon exploration, namely, Chaoshan Depression and Dongsha Uplift in the east of Pearl River Mouth Basin, and south depression in the Liyue Basin. However, the exploration prospect of the Zhongjiannan-Wan'an-western Nanwei Basin area needs further investigation.

Interdecadal variation of TC frequency in Japan

This study analyzed the climate regime shift using statistical change-point analysis on the time-series tropical cyclone (TC) frequency that affected Japan in July to September. The result showed that there was a significant change in 1995, and since then, it showed a trend of rapidly decreasing frequency. To determine the reason for this, differences between 1995 to 2012 (9512) period and 1978 to 1994 (7894) period were analyzed. First, regarding TC genesis, TCs during the 9512 period showed a characteristic of genesis from the southeast quadrant of the tropical and subtropical western North Pacific and TCs during the 7894 period showed their genesis from the northwest quadrant. Regarding a TC track, TCs in the 7894 period had a strong trend of moving from the far east sea of the Philippines via the East China Sea to the mid-latitude region in East Asia while TCs in the 9512 period showed a trend of moving from the Philippines toward the southern part of China westward. Thus, TC intensity in the 7894 period, which can absorb sufficient energy from the sea as they moved a long distance over the sea, was stronger than that of 9512. Large-scale environments were analyzed to determine the cause of such difference in TC activity occurred between two periods. During the 9512 period, anomalous cold and dry anticyclones were developed strongly in the East Asia continent. As a result, Korea and Japan were affected by the anomalous northerlies thereby preventing TCs in this period from moving toward the mid-latitude region in East Asia. Instead, anomalous easterlies (anomalous trade wind) were developed in the tropical western Pacific so that a high passage frequency from the Philippines to the south China region along the anomalous steering flows was revealed. The characteristics of the anomalous cold and dry anticyclone developed in the East Asia continent were also confirmed by the analysis of air temperature, relative humidity, and sensible heat net flux showing that most regions in East Asia had negative values.

Relationship between environmental change on Geoje Island, southern coast of Korea, and regional monsoon and temperature changes during the late Holocene

To reconstruct environmental change during the late Holocene, we investigated sedimentary δ13C values from an exposed section on Geoje Island, on the southern coast of Korea. The δ13C values ranged from −24.3‰ to −21.2‰ and were divided into five stages based on the average value (−22.5‰). A comparison with the regional climate index revealed that wet periods linked to intensified summer monsoon conditions occurred at Stage 1 (4500–3600 cal BP), Stage 3 (1350–900 cal BP), and Stage 5 (300 cal BP to present). Dry intervals were found at Stage 2 (3600–1350 cal BP) and Stage 4 (900–300 cal BP). We found two different vegetational responses to changes in regional temperature and summer monsoons. Stage 3, corresponding to the MWP, was characterized by an association between the δ13C values on the island and the regional temperature, but Stage 4, including the LIA interval, did not show such a relationship. Furthermore, based on comparison with the summer monsoon index, this study suggested that, on the southern coast of Korea, vegetational change was controlled by an MWP-like mode during the warm and wet periods following regional climate change, whereas a LIA-like mode showing independent climate change was dominant during the cold and dry periods. This difference in vegetational changes along the southern coast of Korea and regional (mainly terrestrial-signal based) climate change may be attributed to the influence of sea surface temperature changes in the tropical ocean through the transport of warming seawater by the Kuroshio and Tsushima currents on the East Asian coastal area, including this study area, than on the inner part of the East Asian continent.

Crustal Evolution of a Paleozoic Intra-oceanic Island-Arc-Back-Arc Basin System Constrained by the Geochemistry and Geochronology of the Yakuno Ophiolite, Southwest Japan

The Yakuno ophiolite in southwest Japan is considered to have been obducted by the collision between an intra-oceanic island-arc-back-arc basin (intra-OIA-BAB) system and the East Asian continent during the late Paleozoic. New SIMS (SHRIMP) zircon U-Pb determinations for amphibolite and metagabbro of BAB origin within the Yakuno ophiolite yield ages of 293.4 ± 9.5 Ma and 288 ± 13 Ma, respectively. These ages are slightly older (however, overlapping within analytical errors) than the magmatic age of arc granitoids (ca. 285–282 Ma) that intruded into the mafic rocks of BAB origin. Results from geochronological and geochemical data of the Yakuno ophiolite give rise to the following tentative geotectonic model for the Paleozoic intra-OIA-BAB system: the initial stage of BAB rifting (ca. 293–288 Ma) formed the BAB crust with island-arc basalt (IAB) signatures, which was brought to the OIA setting, and generated the arc granitoids (ca. 285–282 Ma) by anatexis of the BAB crust. A later stage of BAB rifting (&lt;ca. 285 Ma) formed the BAB crust with IAB to MORB signatures, on which the Permian sediments were conformably deposited. These components collided with the eastern margin of the East Asian continent during the early Mesozoic.

Response of the East Asian summer monsoon to large volcanic eruptions during the last millennium

The responses of the East Asian summer monsoon (EASM) to large volcanic eruptions were analyzed using a millennial simulation with the FGOALS-gl climate system model. The model was driven by both natural (solar irradiance, volcanic eruptions) and anthropogenic (greenhouse gases, sulfate aerosols) forcing agents. The results showed cooling anomalies after large volcanic eruptions almost on a global scale. The cooling over the continental region is stronger than that over the ocean. The precipitation generally decreases in the tropical and subtropical regions in the first summer after large volcanic eruptions. Cooling with amplitudes up to −0.3 °C is seen over eastern China in the first summer after large volcanic eruptions. The East Asian continent is dominated by northeasterly wind anomalies and the corresponding summer rainfall exhibits a coherent reduction over the whole of eastern China. An analysis of the surface heat flux suggested the reduction in summer precipitation over eastern China can be attributed to a decrease of moisture vapor over the tropical oceans, and the weakening of the EASM may be attributed to the reduced land–sea thermal contrast after large volcanic eruptions.

Atmospheric concentrations of persistent organic pollutants over the Pacific Ocean near southern Taiwan and the northern Philippines

This study investigates the atmospheric occurrence of persistent organic pollutants (POPs) over the Pacific Ocean near southern Taiwan and the northern Philippines. We determined sixty-six compounds, including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (DLPCBs), polybrominated diphenyl ethers (PBDEs), as well as polychlorinated diphenyl ethers (PCDEs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), and polybrominated biphenyls (PBBs), in air samples simultaneously collected from the offshore oceanic atmosphere (n=6) and over a rural area (n=2). We calculated the atmospheric World Health Organization 2005 toxic equivalency levels (WHO2005-TEQ), for the total dioxin-like POPs, including PCDD/Fs, DLPCBs, and PBDD/Fs, being 0.00612pg WHO2005-TEQ/m3 and 0.0138pg WHO2005-TEQ/m3 over the ocean and land, respectively. We found unexpected lower averaged atmospheric PBDE concentrations in the rural area (15.9pg/m3) than over the ocean (31.1pg/m3) due to higher levels of the BDE209 congener, although the difference was not statistically significant. We have compared and reported our field results with previously published datasets over the global oceans, which suggest PCBs and PBDEs are the dominant chemical contaminants in the global oceanic atmosphere among these halogenated POPs (e.g. PCBs and Σdi-hepta PBDEs could be found in the range of 0.09–48.7 and 8.07–94.0pg/m3, respectively, including our dataset). However, there are still very few investigations on the global atmospheric levels of PBDD/Fs, PCDEs and PBBs and our data sums to these earlier studies. Finally, we point out that the halogenated POPs originated from Taiwan or the continental East Asia which could easily reach remote ocean sites via atmospheric transport.

Cenozoic tectonic jumping and implications for hydrocarbon accumulation in basins in the East Asia Continental Margin

Tectonic migration is a common geological process of basin formation and evolution. However, little is known about tectonic migration in the western Pacific margins. This paper focuses on the representative Cenozoic basins of East China and its surrounding seas in the western Pacific domain to discuss the phenomenon of tectonic jumping in Cenozoic basins, based on structural data from the Bohai Bay Basin, the South Yellow Sea Basin, the East China Sea Shelf Basin, and the South China Sea Continental Shelf Basin. The western Pacific active continental margin is the eastern margin of a global convergent system involving the Eurasian Plate, the Pacific Plate, and the Indian Plate. Under the combined effects of the India-Eurasia collision and retrogressive or roll-back subduction of the Pacific Plate, the western Pacific active continental margin had a wide basin-arc-trench system which migrated or ‘jumped’ eastward and further oceanward. This migration and jumping is characterized by progressive eastward younging of faulting, sedimentation, and subsidence within the basins. Owing to the tectonic migration, the geological conditions associated with hydrocarbon and gashydrate accumulation in the Cenozoic basins of East China and its adjacent seas also become progressively younger from west to east, showing eastward younging in the generation time of reservoirs, seals, traps, accumulations and preservation of hydrocarbon and gashydrate. Such a spatio-temporal distribution of Cenozoic hydrocarbon and gashydrate is significant for the oil, gas and gashydrate exploration in the East Asian Continental Margin. Finally, this study discusses the mechanism of Cenozoic intrabasinal and interbasinal tectonic migration in terms of interplate, intraplate and underplating processes. The migration or jumping regimes of three separate or interrelated events: (1) tectonism-magmatism, (2) basin formation, and (3) hydrocarbon-gashydrate accumulation are the combined effects of the Late Mesozoic extrusion tectonics, the Cenozoic NW-directed crustal extension, and the regional far-field eastward flow of the western asthenosphere due to the India-Eurasia plate collision, accompanied by eastward jumping and roll-back of subduction zones of the Pacific Plate.

Responses of East Asian summer monsoon to natural and anthropogenic forcings in the 17 latest CMIP5 models

AbstractIn this study, we examined the responses of East Asian summer monsoon (EASM) to natural (solar variability and volcanic aerosols) and anthropogenic (greenhouse gasses and aerosols) forcings simulated in the 17 latest Coupled Model Intercomparison Program phase 5 models with 105 realizations. The observed weakening trend of low‐level EASM circulation during 1958–2001 is partly reproduced under all‐forcing runs. A comparison of separate forcing experiments reveals that the aerosol forcing plays a primary role in driving the weakened low‐level monsoon circulation. The preferential cooling over continental East Asia caused by aerosol affects the monsoon circulation through reducing the land‐sea thermal contrast and results in higher sea level pressure over northern China. In the upper level, both natural forcing and aerosol forcing contribute to the observed southward shift of East Asian subtropical jet through changing the meridional temperature gradient.