Strong East Asian Winter Monsoon Research Articles

Anthropogenically-induced atmospheric Pb cycle in low-latitude Asia since the Industrial Revolution recorded by high-resolution stalagmites

The vigorous convective circulation in the low-latitude regions plays an important role in the global lead (Pb) cycle in the context of growing atmospheric Pb pollution. However, the brevity of reconstructions of regional Pb pollution limits our understanding of the low-latitude Pb cycle. Here, we presented continuous stalagmite-based Pb records from Klang (KL) cave in the Thai-Malay peninsula, and complementary stalagmite-based Pb records from Xianrenyan (XRY) cave in upwind region to explore the combined effects of atmospheric circulations and anthropogenic Pb emissions on the regional Pb cycle in the low-latitude regions. The analysis suggests that the XRY records reflect regional Pb pollutions in southern China, while the KL records could represent regional Pb recycling in low-latitude Asia, with the Pb pollutants coming from local and upwind territories (e.g., China, India). Moreover, the Pb variations in peninsular Thailand are significantly influenced by the East Asian Winter Monsoon (EAWM) strength with high (low) amount of Pb pollutants from the upwind territories transported to the study area during the strong (weak) EAWM. However, by comparing KL records with XRY records and other existing geological and meteorological records, we found the EAWM-induced Pb variations in the late 20th century were overwhelmed by unprecedented industry-derived Pb emissions from eastern China. Our findings suggest the ever-increasing anthropogenic emission could surpass the atmospheric circulation controls on the regional Pb cycle, offering a new perspective on understanding the relative influence of natural and anthropogenic forcing.

Glacial sea level low-stands regulated the upper ocean hydrology in the southern South China Sea over the past ∼ 280 kyr

The southern South China Sea (SCS) is an ideal region for investigating the low-latitude climatic and oceanic dynamics in the context of local and global effects. However, records of upper-water hydrography beyond the last two glacial cycles are still limited from the southern SCS. In this study, we present shell δ18O, Mg/Ca and Nd/Ca records of three planktonic foraminiferal species (Globigerinoides ruber, Globigerinoides sacculifer and Pulleniatina obliquiloculata) from Core TX05 to explore changes in upper-water hydrography in the southern SCS over the past ∼280 kyr. The results show that shell δ18O of the three species exhibit more positive values in glacials than interglacials. The δ18O residual (i.e. δ18Osw-ice) calculated by shell δ18O subtracting the signals of ice volume and temperature suggests fresher upper seawaters (lower salinity) during glacials than interglacials. This may be caused by terrestrial freshwater discharge from the paleo-Sunda continent that exposed during glacial sea level low-stands. The freshwater discharge may further be ascribed to relatively abundant precipitation over the paleo-Sunda continent during glacials, possibly pointing to the collective effects of the southward shift of the Intertropical Convergence Zone and the enhanced Pacific Walker circulation. The vertical thermal gradients (ΔTrub-obl and ΔTsac-obl) at Site TX05 show lower values during glacials than interglacials. The SST differences of the southern SCS from the northern SCS (ΔSSTS-N) and from the western tropical Pacific (ΔSSTSCS-WTP) correlate well with indicators from the Chinese Loess section, indicating relatively strong East Asian winter monsoon during glacials. The good correlation of ΔT, ΔSSTS-N and ΔSSTSCS-WTP to the relative sea-level suggests a remarkable effect of sea level low-stands and the strengthened East Asian winter monsoon during glacials on the upper ocean hydrography in the southern SCS.

Varying Relationship between La Niña and SST Anomalies in the Kuroshio and Adjacent Regions during Boreal Winter: Role of the East Asian Winter Monsoon

Abstract The winter sea surface temperature (SST) anomalies in the Kuroshio and adjacent regions (KAR), which greatly influence the East Asian–North Pacific–North American climate, are closely related to El Niño–Southern Oscillation (ENSO). This SST relationship between the KAR and the equatorial eastern-central Pacific is widely assumed to be symmetric between El Niño and La Niña. Compared to previous studies indicating the significant and strong KAR warming during El Niño winters, this study indicates weakly negative KAR SST anomalies in the composite analysis for all La Niña events. Positive winter KAR SST anomalies unexpectedly appear in approximately half of La Niña events, which counteract negative SST anomalies in the rest of La Niña events. Further analysis suggests that the impact of La Niña on KAR SST anomalies is modulated by the East Asian winter monsoon (EAWM) during early winter. The weaker-than-normal EAWM offsets the anomalous northeasterly winds in the KAR induced by La Niña and then reinforces the KAR warming through warm oceanic advection. As for strong EAWM, it enhances the northeasterly winds to the west of an anomalous Philippine Sea cyclone associated with La Niña, leading to KAR cooling with more latent heat flux loss from the ocean and anomalous cold oceanic advection. Additionally, when the EAWM is independent of ENSO and is associated with the western Pacific pattern, it also can exhibit a pronounced influence on the KAR SST anomalies via the major processes of surface latent flux and horizontal heat advection in the ocean, accompanied by a change in Kuroshio transport. Significance Statement The interannual variability of SST from Philippine Sea to the Kuroshio and adjacent regions is considered an important forecast factor of the eastern China climate. Previous studies have reported a dipole SST pattern with Philippine Sea cooling and warming in the Kuroshio and adjacent regions during El Niño winter is dominant, and simply regarded that the effect of La Niña on western North Pacific SST anomalies was a mirror image of that of El Niño events. Here, we have found two distinctive SST patterns in the western North Pacific during La Niña winter. One type is the dipole SST pattern, characterized by Philippine Sea warming and by cooling in the Kuroshio and adjacent regions. The other type is the monopole SST pattern with uniform warming expanding from the Philippine Sea to the Kuroshio and adjacent regions. The dipole (monopole) SST pattern in western North Pacific is modulated by La Niña and a strong (weak) EAWM. Analysis shows that the above two SST patterns during La Niña winter are equally important during 1950–2021. This study has identified the influence of the EAWM independent of ENSO on the SST anomalies in the Kuroshio and adjacent regions.

Grain size and geochemistry characteristics of Core S01-10 from the central Okinawa Trough since 14 ka: Indications for sediment source and the East Asian winter monsoon

Okinawa Trough is a transitional zone between the shallow shelf and the deep ocean, which is covered by a large number of terrigenous materials, recording sea-level fluctuations, tectonic activities, and source-sink during the late Quaternary. Based on grain size and trace element analysis of Core S01–10 from the western continental slope area of central Okinawa Trough, high-resolution paleoenvironment records since 14 ka had been obtained. There is a significant positive correlation between the ratio data of Nb, Th, Sc and REE elements of Core S01–10, which reflects the composition characteristics of terrigenous materials. We use REEs and their discrimination plot of Gd/Yb-Yb and La/Yb-Gd/Yb to conclude that the terrigenous materials mainly came from the Yellow River during 14,000–11,500 a. Moreover, grain size parameters and the provenance discriminant function (DF) show that the transportation of terrigenous materials substance from the main rivers in Chinese Mainland (the Yellow and Yangtze Rivers) to the western slope of central Okinawa Trough is affected by the East Asian winter monsoon. This is mainly manifested in two major stages. During 14,000–11,500 a, these indicators fluctuate on the whole, but in the mass, they indicate a strong East Asian winter monsoon stage, which also leads to the formation and enhancement of the low-temperature underflow, leading to the Yellow River as the dominant source. During 11,500–1920 a, these indicators fluctuated more frequently, reflecting the strengthening/weakening of the East Asian winter monsoon in a shorter period. The tendency of East Asian winter monsoon analyzed by using grain size parameters and DF is consistent with the Ti content of Lake Huguang Maar on the whole, which also verifies the feasibility of the results from the side. Overall, the contribution of substance from the relevant source areas is different in different periods, but Paleo-Huanghe remains the main source. According to the study, the analysis of grain size parameters and trace element in the western slope of central Okinawa Trough can indicate changes of provenance, sea level rising and falling and winter monsoon in this area since 14 ka, which is helpful to explore and reconstruct the sediment provenance and Paleoenvironment evolution in this area since the late Pleistocene.

Influence of Kamchatka Blocking and East Asian winter monsoon on the winter 2m‐temperature over South Korea

AbstractThis study examines the factors affecting the 2m‐temperatures (T2m) in South Korea in winter (DJF) from 1979/1980 to 2018/2019. For this purpose, we performed an empirical orthogonal function (EOF) analysis of the geopotential height at 500 hPa in the region 15°–75°N, 70°E–180° centred around the Korean Peninsula. The first EOF mode, which accounted for 31.1% of the total variance of the winter T2m in the region, is related to the KamChatka Blocking Frequency (KCBF). The second mode, which accounted for 18.3%, is associated with East Asian winter monsoon (EAWM). In addition to EOF analysis, the partial correlation (PC) analysis also confirmed that KCBF Index and EAWM Index, which are highly correlated with the winter T2ms in South Korea, are independent of each other. The individual and combined effects of the KCBF and EAWM are examined because they independently affect the winter T2ms in South Korea. According to the composite analysis, in the years when KCBF is higher than normal (H_KCBF), negative and positive Z500 anomalies are located over the south Sea of Japan and the Kamchatka Peninsula, respectively. In other words, the positive geopotential anomaly over the Kamchatka Peninsula lowers the T2ms of South Korea by blocking the flow of cold air moving eastward from the Korean Peninsula. In the years when a strong EAWM occurred (S_EAWM), negative and positive Z500 anomalies are located over the Manchuria region and the northwestern regions of Russia, respectively. Consequently, cold air in the north moves southward, resulting in lower T2ms in South Korea. For the combined effects of KCBF and EAWM on the T2ms, winters of 40 years are categorized into L_KCBF‐W_EAWM, L_KCBF‐S_EAWM, H_KCBF‐W_EAWM and H_KCBF‐S_EAWM years. The analyses show that when KCBF and EAWM are in phase, the T2ms in South Korea are more prominent than when they are out‐of‐phase.

Recent progress in understanding the interaction between ENSO and the East Asian winter monsoon: A review

This paper reviews recent advances in understanding the interaction between the East Asian winter monsoon (EAWM) and El Niño-Southern Oscillation (ENSO). The achievements are summarized into two aspects: 1) the impacts of ENSO on the EAWM, and 2) effects of the EAWM on ENSO. For the first aspect, the results show that: the current climate model simulations of ENSO impacts on the EAWM have a common weaker bias than in the observations; The influence of central Pacific type ENSO on the EAWM is generally weaker than that of the eastern Pacific type ENSO; The precipitation anomalies in the tropical Indian Ocean tend to contribute to the intra-seasonal transition of ENSO teleconnection over East Asia; The ENSO-EAWM relationship is unstable and subject to non-linear modulation by the state of oceans and extratropical atmospheric phenomena, which include the Pacific Decadal Oscillation and the Arctic Oscillation. Regarding the second aspect, studies have shown that the “pure” EAWM (denoted as EAWMres), which is independent of the ENSO signal, can lead to significant variations in the tropical convection over the western Pacific, the local Hadley circulation over East Asia, and the Walker circulation over the equatorial latitudes; The CMIP6 models can preproduce the above EAWMres effects well, although with some weaker bias. The changes in tropical convection and extratropical zonal flow associated with the EAWMres tend to have a significant modulating effect on the ENSO atmospheric teleconnection over North America. A strong EAWM and a strong Australian summer monsoon coherently provide favorable conditions for the onset of El Niño.

Hydroclimate seasonality from paired coral Sr/Ca and δ18O records of Kikai Island, Southern Japan: Evidence of East Asian monsoon during mid-to late Holocene

The East Asian Monsoon (EAM) modulates the seasonal variability of sea surface temperature (SST), sea surface salinity (SSS), and rainfall in the region. However, seasonal-scale reconstructions showing the hydroclimate response to monsoon intensity shifts in Holocene are limited. We used paired coral Sr/Ca and oxygen isotope (δ18Ocoral) records from modern (1989–2015), 5.7 ka, 4.9 ka, and 3.2 ka corals from Kikai Island, Southern Japan to reconstruct past seasonal variability of hydroclimatic variables. The monthly δ18Ocoral-SSS relationship revealed a statistically significant positive linear correlation (r = 0.63; p < 0.000; n = 310) while the δ18Osw and rainfall showed a statistically significant negative linear correlation (r = 0.55; p < 0.000; n = 93).The large SST and SSS seasonality in 5.7 ka (ΔSSTmax-min = 9.5 °C; Δδ18Omax-min = 1.86‰) and 4.9 ka (ΔSSTmax-min = 10.2 °C; Δδ18Omax-min = 1.45‰) indicate an enhanced seasonal ocean warming which amplified the Western Pacific Subtropical High (WPSH) and the southwesterlies. In contrast, the small SST amplitude in 3.2 ka (ΔSSTmax-min = 7.8 °C; Δδ18Omax-min = 0.98‰) indicates a weakened WPSH and southwesterlies which led to reduced summer rainfall and positive SSS signal. The lower salinity records due to higher rainfall in 7.0 ka, 6.1 ka, 5.7 ka, and 4.9 ka coincide with the strong East Asian summer monsoon (EASM) from 8.2 to 4.7 ka in stacked sediment records. The δ18Ocoral record shows positive SSS driven by weakened summer monsoon rainfall in 4.4 ka, 4.2 ka, 3.8 ka, 3.4 ka, and 3.2 ka.The higher winter SSS (positive δ18Ocoral) and lower winter SST derived from 5.7 ka coral in Kikai Island agree with the strong East Asian winter monsoon (EAWM) intensity from 8.2 to 5.6 ka based on the stacked sediment record. The weak EAWM phase from 5.6 ka to 4.5 ka is consistent with the winter records of warm SST and lower SSS in 4.9 ka. The lower winter SSS and warmer winter SST in 3.2 ka support the evidence of a weak phase around 3.0 ka. The extratropical systems such as the intensified or weakened Siberian High and Aleutian Low have affected the northeasterly EAWM and consequently influenced the variability of winter SST and SSS in subtropical southern Japan in mid- and late Holocene.

Zooplankton Fecal Pellet Characteristics and Contribution to the Deep‐Sea Carbon Export in the Southern South China Sea

AbstractZooplankton fecal pellets play a significant role in particulate organic carbon (POC) export, which has been widely reported in different ocean regions. However, zooplankton fecal pellet in the tropical marginal sea and its contribution to the total POC flux has not been sufficiently investigated yet. Here, for the first time we report zooplankton fecal pellet characteristics and fluxes in the South China Sea from June 2020 to May 2021 via one mooring with two sediment traps deployed at 500 and 2,190 m depths. Average fecal pellet numerical flux was 2.30 × 104 and 4.22 × 104 pellets m−2 d−1 at 500 and 2,190 m, respectively, corresponding to average fecal pellet carbon (FPC) flux from 0.31 to 0.71 mg C m−2 d−1. Small ellipsoidal and spherical pellets accounted for more than 90% of the total numerical flux, while large cylindrical pellets, although relatively rare (6%), accounted for almost 15% of the FPC flux. Both fecal pellet numerical and carbon fluxes were higher in winter, when the strong East Asian winter monsoon winds and heavy rainfall promoted the marine primary production. Higher fecal pellet fluxes combining with the presence of extra‐large pellets at 2,190 m compared to those at 500 m suggested the in‐situ repackaging of deep‐dwelling zooplankton communities in the mesopelagic and bathypelagic zones. Contribution of fecal pellets to the total POC flux ranged from 0.4% to 30.0% (averaging 9.0%), with higher values occurring during winter monsoon, at which time fecal pellets became a critical conveyor of carbon export to the deep sea.

Spatial variations of particulate-bound mercury in the atmosphere along a transect from the mid-Northern Hemisphere to the high southern latitudes

Particulate-bound mercury (PBM) measurements in the boundary layer were performed during the 2015–2016 Chinese Antarctic Research Expedition from the middle Northern Hemisphere (Shanghai, China) to the Antarctic Ice Sheet summit, Dome A. A significant latitudinal gradient in PBM was observed. PBM over the Northern Hemisphere oceans was influenced by both continental and oceanic sources, with elevated PBM levels associated with continental inputs. PBM over this region was significantly higher in November than that in April, which could be related to the continental Hg carried by the strong East Asian winter monsoon. Far away from the continental sources, extremely low PBM was observed over the Southern Ocean (2.6 ± 1.6 pg m−3). Elevated PBM was found across the Antarctic Ice Sheet (79.1 ± 43.4 pg m−3), and the highest PBM observed at Dome A (143.4 ± 27.0 pg m−3) was likely associated with GEM emissions from snow and enhanced oxidation of GEM due to snow photochemistry. Across the Antarctic Ice Sheet, PBM increased significantly with the increasing distance from the coast, which may have resulted from the mixing of air masses from the Antarctic plateau and the ocean. GEM emissions from inland Antarctic snow can influence atmospheric PBM concentrations over the Antarctic coastal seas via the transport by katabatic winds, and thus play an important role in atmospheric Hg cycle in the high southern latitudes.

History of coastal dune evolution in the Fujian region of southeastern China over the last millenium

Coastal dunes are a product of the evolution of the coastal environment. Previous research shows that dune development in the Fujian coastal region correlates well with the fluctuations of East Asian winter monsoon (EAWM) and sea level. However, comparison of coastal dune evolution along the Fujian coast since 1 ka with various paleoenvironmental indicators shows that, in addition to EAWM and sea level change, increased frequency and intensity of typhoon landfalls and tropical cyclone may have played an important role in dune building. Here we present the results of optically stimulated luminescence (OSL) dating and analyses of lithostratigraphy, grain size, and color of late Holocene aeolian sediments from Shenhu Bay of the Fujian coast, Southeastern China. Together with published chronological data from the region, three phases of coastal aeolian activity are defined: ~1050–1300 CE (the Medieval Climatic Anomaly, MCA), ~1450–1700 CE (early Little Ice Age, LIA), and ~ 1750–1930 CE (late LIA). These phases of sand accumulation had different sand sources: the source for the two phases of ~1050–1300 CE and ~ 1450–1700 CE was the reworking of the adjacent “old red sand”, and that for the phase of ~1750–1930 CE was beach and/or foredune sand. During ~1050–1300 CE, although the sea level was relatively high and the beach sand source was relatively limited, the increased frequency of typhoon landfalls and the widely distributed “old red sand” deposits provided important dynamic and provenance conditions for the formation of coastal dunes. During ~1450–1700 CE, strong EAWM and increased frequency of typhoon landfalls were all conducive to aeolian activities. On the contrary, the strong aeolian activity during ~1750–1930 CE may be related to sea level drop and strong EAWM.

Monsoon- and ENSO-driven surface-water pCO2 variation in the tropical West Pacific since the Last Glacial Maximum

The East Asian monsoon (EAM) and El Niño-Southern Oscillation (ENSO) are large-scale oceanic-atmospheric fluctuations that dominate climate variability in the tropical Pacific Ocean. Although the effects of EAM and ENSO on physical and biological processes are increasingly understood, little is known about their influence on seawater carbonate chemistry in the tropical Pacific, especially in the geological past. Here, we present reconstructed variations in surface-water pCO2 (pCO2(sw)) and their deviation from atmospheric pCO2 (ΔpCO2(sw-atm)) in the western Philippine Sea (WPS) since 27 ka. Our record displays covariation between ΔpCO2(sw-atm) and the intensity of the East Asian summer monsoon (EASM) since the Last Glacial Maximum (LGM), suggesting that EASM-driven upwelling controls long-term changes in surface-water carbonate chemistry and air-sea CO2 fluxes. Rapid changes in ΔpCO2(sw-atm) were linked to the ENSO-like state and, to a lesser extent, the East Asian winter monsoon (EAWM) during the Last Deglaciation, with low values corresponding to La Niña-like phases and strong EAWM during Heinrich Event 1, the Allerød and the Younger Dryas, and high values corresponding to El Niño-like phases and weak EAWM during the Bølling and Pre-Boreal. This interpretation is supported by the relationship of EAM and ENSO to modern surface-water carbonate chemistry in the WPS. Our new record, combined with previously published data, suggests that the tropical Pacific played a minimal role in sequestering CO2(atm) during the LGM. Tropical Pacific surface waters overall became a pronounced CO2 source to the atmosphere during the Last Deglaciation, possibly making a substantial contribution to the deglacial pCO2(atm) rise. We infer that this flux was mainly due to ENSO-related patterns of vertical stratification or lateral advection, perhaps in addition to equatorial upwelling of southern-sourced waters already enriched in dissolved inorganic carbon. Our findings indicate that tropical conditions (i.e., EAM and ENSO-like state) played a crucial role in glacial-interglacial pCO2(atm) changes, suggesting that this is an important area for future research into the causes of glacial pCO2(atm) cycles.

Linkage of Strong Intraseasonal Events of the East Asian Winter Monsoon to the Tropical Convections over the Western Pacific

The East Asian winter monsoon (EAWM) is the most important climate system for transporting Arctic cold air to the tropics in boreal winter. Rapid intensification of the EAWM, such as a cold surge, can lead to increased tropical convection over the western Pacific, but the possible effects from the intraseasonal variation of EAWM is unclear. Using high temporal and spatial resolution satellite data, including Outgoing Longwave Radiation (OLR) and Tropical Rainfall Measuring Mission (TRMM) precipitation, we show that strong intraseasonal EAWM events are associated with increased tropical convection over the western Pacific for about 6–8 days. Our statistical analysis shows that the lifetime of a strong intraseasonal EAWM event is about 2 weeks, with the beginning, peak, and ending phases occurring at days −6, 0, and 6, respectively. During days 0 to 8, increased convection is observed over the western tropical Pacific, due to the anomalous convergence associated with the strengthened northerly winds over the South China Sea. Over land, increased precipitation is observed over Vietnam, northwestern Kalimantan, and the southern Philippines. In addition, the East Asian local Hadley circulation is strengthened during these days, in association with the enhanced tropical convection.

Early Pleistocene (Marine Isotope Stage 40–36) paleoceanography in the northwestern Pacific: Evidence from faunal and oxygen isotope analyses of planktonic foraminifera

The Mid-Pleistocene Transition (MPT) is characterized by a shift from a 41-kyr to a 100-kyr climate cycle of approximately 1.25–0.7 Ma. However, proxy records before the MPT are sparse in the northwestern Pacific region. To investigate the marine environment around the oceanographic convergence zone of the northwestern Pacific prior to the MPT, we conducted biostratigraphic and oxygen isotope analyses of planktonic foraminifera derived from the upper part of the Kiwada Formation of the Kazusa Group, which is distributed in the Boso Peninsula, central Honshu, Japan. The interval investigated was deposited from Marine Isotope Stages (MIS) 41 to 36 (ca. 1.31–1.20 Ma). The last occurrence of Globigerinoides obliquus is emplaced 30 m above the tephra layer Kd1 during MIS 37. The first occurrence of Neogloboquadrina inglei is placed somewhere below the tephra layer Kd8 and is older than 1.310 Ma. Time-series environmental proxy changes in the planktonic foraminiferal assemblages and oxygen isotopes suggest that the marine environment off the Boso Peninsula was influenced by the Kuroshio Current and the transitional water close to the Kuroshio Front, while the latitudinal shifts of the Kuroshio Front were associated with the glacial-interglacial periods prior to the MPT. Our results suggest that obliquity variability played a significant role in the mid-latitude Pacific Ocean before the MPT, and the hydrographic change in the North Pacific Subtropical Gyre seems to be connected to high-latitude climatic changes. Moreover, the temporary southward migration of the Kuroshio and Subarctic fronts occurred during the late MIS 38, which may be associated with the stronger East Asian winter monsoon. Thus, mid-latitude Pacific oceanographic changes that occurred before the MPT may be linked not only to global remote connections but also to local atmospheric circulation. • We conducted the biostratigraphic and oxygen isotope analyses of the planktonic foraminifera in the Kiwada Formation, central Japan. • The last occurrence of Globigerinoides obliquus was correlated with the late MIS 37. • Palaeoceanographic changes in the mid-latitudes seems to be connected to high-latitude climatic changes.

The Seesaw Pattern of PM2.5 Interannual Anomalies Between Beijing‐Tianjin‐Hebei and Yangtze River Delta Across Eastern China in Winter

AbstractSince 2013, the winter mean fine particulate matter (PM2.5) had been decreased significantly due to stringent emission controls in most of China. Nevertheless, we found a seesaw pattern of PM2.5 interannual anomalies between Beijing‐Tianjin‐Hebei (BTH) and Yangtze River Delta (YRD). Using the multiple linear regression method, meteorology‐driven PM2.5 interannual anomalies show that the low (high) PM2.5 relative difference between BTH and YRD (RDB&amp;Y) was associated with the strong (weak) East Asian winter monsoon (EAWM). The strong EAWM transported more air pollutants from BTH to YRD. During the COVID‐19 lockdown period, due to the weak EAWM, air pollution still occurred in northern BTH, while the PM2.5 was relatively low in YRD, causing high RDB&amp;Y values. Our results imply that the activity of EAWM and characteristics of regional transport have obvious interannual variations, which is indispensable in evaluating the achievements of PM2.5 quality management between up and downstream regions.

Holocene aeolian dust accumulation rates across the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is a major region of Quaternary aeolian dust deposition. However, the temporal and spatial variations of Holocene aeolian dust accumulation rate (DAR) across the CLP have not been systematically evaluated. Here, we present a synthesis of Holocene DARs across the CLP based on 36 well-dated loess sections. The results show that the DAR was relatively high during the early Holocene, lowest during the mid-Holocene, and increased substantially during the late Holocene. These trends are in good agreement with the temporal variations of the East Asian summer monsoon (EASM). We conclude that the dominant factor controlling dust storm activity across the CLP during the Holocene was EASM precipitation, rather than the East Asian winter monsoon (EAWM). However, during intervals of a strong EAWM there was a significant positive correlation between the DAR in the CLP and dust deposition in Greenland, suggesting that a strong EAWM may have elevated Asian desert dust to high altitudes, enabling it to be entrained by the westerly jet and transported for long distances. Anthropogenic influences may be superimposed on EASM-modulated dust activity. Against the same background of EASM precipitation, the DAR after 4 kyr BP was significantly higher than previously, which may be related to the intensification of human activities in the dust source areas. Notably, several intervals of high DAR during the past 2000 years were not accompanied by decreases in EASM precipitation, and instead they correspond to significant population increases in the dust source areas. • Holocene dust accumulation rates across the Chinese Loess Plateau were assessed. • EASM dominated Holocene dust storm activity across the Chinese Loess Plateau. • Anthropogenic impacts on dust activity can be traced back to at least 4 kyr BP.

Impact of Autumn-Winter Tibetan Plateau Snow Cover Anomalies on the East Asian Winter Monsoon and Its Interdecadal Change

The present study investigates the impacts of autumn-winter Tibetan Plateau (TP) snow cover anomalies on the interannual variability of the East Asian winter monsoon (EAWM). It is found that the northern component of EAWM is significantly associated with October-November-December-January (ONDJ) snow cover anomalies over the eastern TP, whereas the TP snow cover changes have little impact on the southern component of EAWM. However, the relationship of the northern component of EAWM to ONDJ TP snow cover experienced an obvious change in the mid-1990s. During 1979–1998, due to the high persistence of TP snow anomalies from autumn to winter, extensive ONDJ TP snow cover anomalies have a prominent influence on atmospheric circulation over Asia and the North Pacific, with more TP snow cover followed by an enhanced Siberian high and a deepened Aleutian low in winter, resulting in stronger EAWM. During 1999–2016, TP snow cover anomalies have a weak persistence. The atmospheric circulation anomalies display a different distribution. As such, there is a weak connection between the northern component of EAWM and the TP snow cover anomalies during this period.

Sea surface temperature seasonality in the northern South China Sea during the middle Holocene derived from high resolution Sr/Ca ratios of Tridacna shells

AbstractSeasonal climate variability is an important component of Earth's climate system, and has a significant impact on ecosystems and social systems. However, the temporal resolution of most proxy-based paleoclimate records is limiting to fully understand the past seasonal changes. Here, we used high-precision monthly resolution Sr/Ca records of three Tridacna squamosa specimens from the northern South China Sea (SCS) to reconstruct the sea surface temperature (SST) seasonality during three time periods from the middle Holocene. The results suggested that SST seasonality in the northern SCS during the middle Holocene (3.21 ± 0.98°C) was smaller than that for recent decades (AD 1994–2004, 4.32 ± 0.59°C). Analysis of modern instrumental data showed that the SST seasonality in the northern SCS was dominated by the winter SST, which was deeply influenced by the intensity of East Asian winter monsoon (EAWM). A strong EAWM usually resulted in cooler winter SST and a larger SST seasonality in the northern SCS. The reconstructed Holocene EAWM records showed that the EAWM strengthened from the middle to late Holocene, which was seen in our reconstruction of less SST seasonality changes during the middle Holocene in the northern SCS. This study highlighted that the Sr/Ca ratios from Tridacna shells can be used as a potential high-resolution indicator of past seasonal climate changes.

Air Pollution Zone Migrates South Driven by East Asian Winter Monsoon and Climate Change

AbstractA variety of climatological indices have been established to illustrate the impact of climate change on air pollution in China, but major facts for causing variations of air pollution attributed to climate change are still unclear. Here, using in‐situ PM2.5 (particles with the aerodynamic diameter less than 2.5 μm) measurement, atmospheric reanalysis data and a chemical transport model, we show that meridional distribution of PM2.5 loadings is strongly modulated by the intensity of East Asian winter monsoon (EAWM). The EAWM drives the heavily polluted zone in eastern China to migrate southward, i.e., under stronger EAWM, more southward migration of air pollution occurs. We expect that the migration will likely re‐distribute carbon sources‐ and sinks‐related ecosystem, posing a new challenge for the Chinese government, who needs to implement region‐different emission reduction plans in the future, to mitigate air pollution and to go carbon neutral.

Interdecadal Variation of the Wintertime Precipitation in Southeast Asia and Its Possible Causes

AbstractBased on several observational and reanalysis datasets for the winters 1901–2017, this study investigates the interdecadal (ID) variation of the Southeast Asian rainfall (SEAR) and its potential drivers. The dominant mode of the wintertime SEAR on the ID time scale features enhanced precipitation over the eastern Maritime Continent and the Philippines and a slight decrease of precipitation over the western Maritime Continent, or the opposite sign. The ID SEAR variability peaks at the 8–16-yr period and explains more than 20% of the total variance regardless of the datasets and period considered, highlighting the importance of the ID variability of the SEAR. The atmospheric circulation that facilitates abundant ID SEAR is characterized by enhanced lower-tropospheric wind convergence and cyclonic anomalies over the South China Sea and the Philippines. On the one hand, this wind convergence is attributed to the enhanced Walker circulation induced by the negative phase of the interdecadal Pacific oscillation (IPO). On the other hand, it is attributed to the enhanced northerly anomalies along the coast of East Asia induced by a strong East Asian winter monsoon (EAWM) and reduced autumn Arctic sea ice in the Barents–Kara Seas. These mechanisms are further confirmed by model experiments from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The effects of the IPO, EAWM, and Arctic sea ice on the SEAR are mostly independent. They together explain approximately 70% of the SEAR variance on the ID time scale.

Geochemical and Isotopic Evidence for Provenance of the Western Sea of Japan Over the Last 30000 Years

The Sea of Japan (JS) is a unique marginal sea in the western North Pacific that is characterized by four shallow straits. It can provide information about the paleoenvironment, for instance indicating variations in the East Asian Monsoon, Tsushima Warm Current, sea ice coverage, and Westerly Jet. Compared with other marginal seas in the western North Pacific, the JS is currently the only marginal sea without influx from large rivers. It is, therefore, of interest to determine the source of terrigenous sediments over time, particularly in the western JS, which has been less investigated in previous reports. In this study, a suite of multi-proxies including Sr and Nd isotopes and minor elements were measured for fine fractions (&amp;lt;63 μm) of core LV53-18-2 that were recovered from the western JS over the last 30 ka. Our results show that the sediments are rich in volcanic detritus and that the provenance of terrigenous sediments in the western JS is mainly derived from the arid region in northern China and coastal areas in the Far East. During the Last Glacial Maximum, the increased coverage of sea ice may have contributed to the accumulation of terrigenous debris. Meanwhile, the stronger East Asian Winter Monsoon and expansion of the Westerly Jet over northern China also carried more dust to the study area. However, the weakened atmospheric circulation and rise in sea level, induced by the ascending boreal insolation during the last deglaciation and early Holocene, remarkably reduced input of terrigenous debris, and the intense melting of sea ice delivered an amount of detritus from coastal areas to the research area. After 8 ka, the high stand sea level and opening of the Tatar Strait may have led to the development of the Liman Cold Current, which transports large quantities of volcanic materials to the study area continuously and produces more positive Eu anomalies, radiogenic εNd, and depleted ΣREE.