East Asian Winter Monsoon Intensity Research Articles

Industrially induced warming triggered synchronous intensity changes in the East Asian summer and winter monsoons

Anomalies in the East Asian monsoon system significantly disrupt the densely populated East Asian region, underscoring the importance of understanding such changes and improving current predictive abilities. On the basis of instrumental records, previous studies have shown that the East Asian winter monsoon (EAWM) and summer monsoon (EASM) interact with each other. However, owing to the lack of long-term high-resolution EAWM records, it remains unclear how and whether human activity has affected the phase relationship between the EASM and EAWM since the Industrial Revolution. In this study, we present a precisely dated high-resolution EAWM record for the last 300 years from a crater lake in northeastern China. Our results indicate that the EAWM intensity was relatively weak and fluctuated significantly between 1700 and 1850 CE. After 1850 CE, the EAWM strengthened rapidly and exceeded its intensity observed at the end of the Little Ice Age. In addition, a comparison of our reconstructed EAWM record with the published EASM record clearly shows in-phase variations during the Current Warm Period. We concluded that the climatic effects of industrially induced warming enhance the EAWM by slowing the Atlantic meridional overturning circulation and increasing the meridional temperature gradient, while also strengthening the EASM by increasing hemispheric meridional gradients and affecting other large-scale processes. Under the sustained intensification of human activity, the EASM and EAWM are likely to continue exhibiting synchronous variations in the future.

Early Pleistocene Orbital‐Scale Variability in Australian Northwest Shelf Sediments

AbstractPaleoclimate proxy records from regions sensitive to humidity/aridity extremes provide crucial insights into the natural forcing mechanisms underlying long‐term climate variability in broader regions. One such area is Northwest Australia, where the Australian monsoon impacts its northernmost fringes, which are bordered by the Great Sandy Desert inland. Marine sediments from the Australian Northwest Shelf record fluvial run‐off and eolian dust input during the wet and dry seasons, respectively. The location is therefore ideal for investigating long‐term variability in the Australian monsoon and Northwest Australian dust flux over orbital timescales. However, there are few continuous, high‐resolution paleoclimate records from this region spanning the early Pleistocene, when strong ice‐climate feedbacks of the late Pleistocene did not yet dominate global climate. Here, we present geochemical and environmental magnetic proxy records that reveal %CaCO3 and dust‐flux variability between 2.9 and 1.6 million years (Myr) ago from International Ocean Discovery Program Expedition 356 Site U1464 on the Australian Northwest Shelf. We establish a new, orbitally‐tuned chronology for Site U1464, primarily based on ∼400 thousand year (kyr) eccentricity cyclicity in %CaCO3, and observe strong obliquity variability (41 and 54 kyr periodicities) but almost no precession signal in the dust‐flux records. We propose that the 41 kyr cycle in Northwest Australian dust flux could be a linear response to East Asian winter monsoon intensity and/or the summer inter‐tropical insolation gradient (SITIG), whereas the 54 kyr cyclicity might be a non‐linear response to obliquity amplitude modulation via the SITIG effect on the cross‐equatorial atmospheric circulations.

East Asian monsoon and westerly jet driven changes in climate and surface conditions in the NE drylands of China since the Late Pleistocene

The East Asian summer monsoon (EASM) is a major component of the global climate yet, the causes for the past spatiotemporal variability of EASM rainfall, its interactions and impacts remain unresolved. Here we use the Sr–Nd isotopes and rare earth elements composition of dust in a peat record from northeast (NE) China to investigate the relationship between aeolian dust, the East Asian monsoon and Westerly Jet (WJ) over East Asia since the Late Pleistocene (14 cal ka BP). The NE drylands of China dominate the dust fraction (Hunshandake, Horqin; 44–88%) with a contribution from the deserts of NW China (Badain Jaran, Tengger, Taklamakan; 10–44%), suggesting an influence of the WJ. Dust deposition varied during the Holocene, displaying a minimum between 8.0 and 6.0 cal ka BP and two peaks at 5.8–3.8 and 1.7–0.3 cal ka BP. Changes in dust flux are opposite to the East Asian winter monsoon intensity profile, suggesting a limited influence of the winter monsoon. The EASM appears to have played a more significant role in the dust cycle, with increasing dust fluxes corresponding with lower EASM precipitation. Variations in dust flux from NE drylands display shifts reflecting changes in EASM precipitations and dune activity along the EASM margin, where the dust originates from. To account for the influence of the WJ, we propose that the meridional position and intensity of the WJ also affected dust emission in the drylands’ region. A more northward position of the WJ allows the EASM front further north, generating more precipitations over the NE drylands, reducing the extent of arid areas, and resulting in less dust emission from dune activity, while the opposite occurs with a strong, more southerly WJ. Anthropogenic activities are likely to have had an increasing impact on the dust cycle over the late Holocene. Nevertheless, the presence of inconsistencies in records, coupled with a simultaneous decline in climatic conditions (mainly precipitations) during the same timeframe, hinders the precise assessment of the influence of human activities on dust emissions in the region.

Mid-Holocene pine forest expansion caused by the weakening of the East Asian winter monsoon and linked to climate change in the North Atlantic region

The East Asian winter monsoon (EAWM) system is one of the most active components of the global winter atmospheric circulation, and it has a major impact on the Eurasian climate in winter. However, relatively few proxy indicators are available to reconstruct the past evolution of the EAWM. Based on the physiology and modern distribution of the temperate forest and boreal forest in Northeast Asia, we found that the northern boundary of temperate pine forest is sensitive to winter temperature and thus it can be used as a proxy for EAWM intensity. A Holocene pollen record from Lake Woniupaozi in Northeast China shows that an expansion of temperate pine forest since ∼6.0 ka cal BP was linked to a weakening of the EAWM. This pattern is consistent with other paleoclimatic records from Northeast Asia and elsewhere, including the North Atlantic region, Middle East, Arabian Sea, and the Tibetan Plateau/Southwest China, which suggests a major climatic transition in the mid-Holocene. The mechanism responsible for this teleconnection may have been the continuous melting of the Laurentide ice which lowered the SST in the North Atlantic and maintained the North Atlantic Oscillation (NAO) in a positive winter phase. This influence was subsequently transmitted from the North Atlantic region to Eurasia via the winter southern Eurasian (SEA) teleconnection.

High-resolution luminescence chronology of loess-paleosols reveals East Asian summer monsoon and winter monsoon variation in Hexi Corridor during the past 25 kyr

The variability and interaction of the East Asian summer monsoon (EASM), East Asian winter monsoon (EAWM) and Westerlies dominate mid-latitude Asian hydroclimate and influence over a billion lives in Asia. However, how variation in the EASM, EAWM and Westerlies influences climate change in their transition zones in NW China remain unclear. Specifically, how these atmospheric systems interact during strong-weak phases variation over different timescales is still hotly debated. This study investigates four loess-paleosol sequences in the transition zone between EASM and Westerlies-influenced areas along the central Hexi Corridor of NW China, and presents 63 quartz optically stimulated luminescence (OSL) ages to generate the most detailed chronology for any loess record within the Hexi Corridor. In combination with sedimentology, proxy indexes of magnetic parameters (χlf, χfd, χARM/SIRM) and grain size of these loess-paleosol sequences, and TraCE-21 ka climatic modelling, the loess deposition and climatic changes at central Hexi Corridor regions over the past 25 ka are reconstructed. Our results indicate that: (1) loess deposition initiated by at least 25 ka at Hexi Corridor. Loess depositional rates decrease from late last glacial into the Holocene, with maximum accumulation rates (140–180 g/cm3/ka) occurring during the Last Glacial Maximum. Depositional hiatuses up to 8 ka are recognized in late Quaternary Hexi Corridor loess, which suggests that high-resolution chronologies are necessary for robust paleoclimatic reconstructions from loess records in the region. (2) Over glacial-interglacial cycles, climate in the Hexi Corridor demonstrates a cold-dry glacial and a warm-moist interglacial, consistent with moisture changes observed in the monsoonal Chinese Central Loess Plateau and Westerlies-dominated Central Asia. However, moisture in central Hexi Corridor increased from the early Holocene to mid-Holocene, with a wettest period at 8–7 ka, and followed by a relatively wet late Holocene. These changes are most consistent with the EASM-dominated Chinese Central Loess Plateau and suggests that Westerlies influence in the central Hexi Corridor is minor over at least the past 25 kyr. (3) EAWM intensities demonstrate an anti-phase relationship to EASM intensities over the past 25 kyr in the Hexi Corridor, with decreasing EAWM intensity into the early-mid Holocene and an increase into the late Holocene. (4). EASM precipitation variability in the Hexi Corridor appears to not to be a direct nor singular response to changes in 30°N summer insolation. EASM lags insolation by 3 kyr during the Holocene, supporting the idea that high-latitude forcing through changes in ice volume, greenhouse gases, and/or meltwater input to North Atlantic and Southern oceans can effectively modulate EASM intensity and critically influence Hexi Corridor paleoclimatic conditions.

High‐Resolution Records of Millennial‐Scale East Asian Winter Monsoon in the Shelf Sea of Eastern China

AbstractThe evolution of the East Asian winter monsoon (EAWM) during the Holocene remains controversial because of the lack of reliable proxies. In this study, a link between cross‐front transport and the EAWM was found in the North Yellow Sea, and the EAWM intensity could be imprinted in the leaked sediment, which permits reliable reconstruction of the EAWM on well‐preserved offshore deposition. By comparison with instrumental data, the wind speed of the EAWM since 4.4 ka was quantitatively reconstructed for the first time at high resolution (∼5 yr). The results show that the EAWM gradually weakened in the mid‐to‐late Holocene, which was likely controlled by solar insolation, and that there has been a negative relationship between the EAWM and temperature on the centennial scale since ∼2.0 ka; this relationship was reversed by increasing CO2 emissions during the Current Warm Period.

Provenances of the Oldest Xiashu loess and Xuancheng loess in southern China: Implications for dust transport and dust proxies of the East Asian winter monsoon

The loess-paleosol sequences of southern China are valuable paleoclimatic archives since the Middle Pleistocene, on the regional and global scales. Knowledge of loess provenance can shed light on dust transport and the development of paleoclimatic proxies for loess deposits. However, there is a research gap regarding the provenance of the Oldest (∼0.9 Ma) Xiashu loess near the Yangtze River valley. The precise source area of the Xuancheng loess in southern China remains to be unidentified. In this study, we used elemental geochemistry and detrital zircon UPb ages to identify the sources of the Oldest Xiashu loess and Xuancheng loess in southern China. The Oldest Xiashu loess is dominantly derived from Yangtze River sediments, and part of its fine-grained dust component originates from the arid regions of Central Asia or northern China. The elemental compositions of the size-fractionated silicates and detrital zircon UPb ages of the Xuancheng loess are like those of the Shuiyang River sediments in the Xuancheng region. These results demonstrate that the Xuancheng loess is mainly the product of local dust activity in the Xuancheng regions, and thus that the Xiashu and Xuancheng loess are the products of independent dust transport processes. This spatial differentiation of loess provenance may be a widespread phenomenon in southern China, and consequently, the grain size compositions of the various loess sections in southern China cannot be used to recover paleo-wind directions on a regional scale. Overall, our study shows that when the grain size compositions from the southern China loess are used to reconstruct East Asian winter monsoon intensity, the signals from local wind fields should first be removed.

Paleoclimates inform on a weakening and amplitude-reduced East Asian winter monsoon in the warming future

AbstractThe East Asian winter monsoon (EAWM) has significant impacts on the weather and climate, and subsequently on the economy and society, in East Asia during boreal winters, and its projection into the future is scientifically and practically significant. However, projections relying on geological EAWM reconstructions, which can compensate for instrumental record limitations, are still lacking and urgently needed. It is more promising to conduct prediction under the background of not only instrumental but also geological changes in the EAWM. We used grain-size records from four high-resolution, chronologically well-defined loess sections on the Chinese Loess Plateau to represent past EAWM intensity and its amplitudes. Our results show that the EAWM is weaker and has lower amplitudes during warm periods than during cold stages at various time scales. Moreover, instrumental records reveal that the EAWM shows a weak level and reduced interannual amplitudes after the mid-1980s under the context of global warming. We propose that the EAWM will experience long-term weakening and reduced (e.g., interannual) amplitudes under 21st century global-warming scenarios.

Distinct effects of winter monsoon and westerly circulation on dust aerosol transport over East Asia

The transport of dust aerosol in East Asia is affected by the East Asian winter monsoon (EAWM) and westerly circulation both for modern and geological periods. There are obvious seasonal changes in the intensity and range of EAWM and westerly jet; however, their impacts and relative contributions to East Asian dust transmission are still unclear. In this study, we use Regional Climate Model 4 (RegCM4) to simulate the changes in the East Asian dust cycle under present conditions, assessing the effects of EAWM and westerly jet on dust transport. The results show that the dust at the upper level is mainly transported by the westerly circulation, while that of the lower layer is mainly transported by the EAWM. In March, the westerly jet is located on the south side of the Tibet Plateau, and the high-level dust aerosol is transmitted eastward to the northern Pacific. Low-level dust is transmitted to the southeastern China with the influence of EAWM. With the northward shift of the westerly jet, the control range of the westerly winds increases in May and their correlations are weakened. In contrary, the impact of EAWM on the lower layer dust is enhanced. Due to the strengthened interaction between the westerly winds and the EAWM, they can both affect the middle-level dust transmission. The effect of EAWM is sensitive to the dust particle sizes. Under the action of EAWM, fine-grained dust is transmitted far away, while coarse-grained dust is limited to the vicinity of the source area. Once the dust is carried to the westerly layer, the influence of westerly winds on the transmission of different particle sizes dust is similar.

Association of the Zonal Migration of North Pacific Storm Track With the East Asian Monsoon in Boreal Wintertime

AbstractThe winter North Pacific storm track (WNPST) distinctly manipulates weather and climate in the midlatitudes. Thus, it is necessary to comprehend the factors and related mechanisms governing the location and intensity of WNPST. In the present study, the influence of the East Asian winter monsoon (EAWM) on the zonal movement of the WNPST represented by the lower‐tropospheric meridional eddy heat flux is investigated, and the possible physical processes are analyzed. There is a significantly positive correlation, especially interannual signal, between the strength of the EAWM and the zonal position of the WNPST. The Liang‐Kleeman information flow theory is used to prove the mutual causality between the intensity of EAWM and the zonal migration of WNPST. The EAWM‐related intensity anomaly pattern of the WNPST, with prominently negative anomalies over the northwest Pacific and significantly positive anomalies over the northeast Pacific, is associated with the eastward movement of the WNPST. In addition, the results show that the patterns of anomalous lower‐tropospheric atmospheric baroclinicity and barotropic energy transfer do not match the EAWM‐related anomalous WNPST. The upper‐tropospheric jet anomalies may be related to the weakening in the peak area and the western flank of the climatological WNPST. The impact of the EAWM on the zonal movement of the WNPST can be related to the anomalous baroclinic energy transfer and buoyancy conversion. Furthermore, the moisture effect including anomalous meridional and vertical eddy moisture flux may also play a role by latent heat release.

Lateral sediment transport and late Quaternary changes of eolian sedimentation in the East Sea (Japan Sea)

• GSDs reveal offshore limit of lateral sediment transport in the East Sea. • Lateral sediment transport from the Korean Peninsula is within ~70 km offshore. • Eolian sediments in the SKP were transported by upper westerlies and winter monsoons. • East Asian winter monsoon intensity controlled eolian sedimentation in the East Sea. We investigated grain size records of a sediment core (05-P21) from the South Korea Plateau in the East Sea, located ca. 270 km east of the east coast of the Korean Peninsula. To verify an exclusive eolian origin for the detrital components of the sediments, we first examined how far offshore lateral-sediment-transport contributions from the eastern margin of the Korean Peninsula could reach, based on spatial changes in the grain size distribution (GSD) of surface sediments. To distinguish grain populations representing different transport processes, we performed end-member analyses (EMAs) of the GSDs of detrital fractions using the AnalySize software. EMA of the surface sediment GSDs showed that they consist of three end-member (EM) grain populations representing contributions from lateral (EM1 and EM2) and eolian transport (EM3). EM contributions by lateral transport reached only ca. 70 km seaward, confirming the exclusive eolian origin of detrital components of the 05-P21 core sediments. EMA of GSDs of the 05-P21 sediments distinguished two EM grain populations with fine (3.6 µm) and coarse (9.5 µm) median sizes, suggesting transport by upper westerlies and winter monsoon northwesterly surface winds, respectively. Variation in the proportions of fine and coarse EMs since ca. 186 ka indicated controls by both orbital and sub-orbital scale changes in intensity of the East Asian winter monsoon in association with global ice volume changes and Dansgaard–Oeschger cycles.

Pollen records of orbitally modulated variation in East Asian winter monsoon intensity and freshwater inflow to the Ulleung Basin of East Sea, South Korea, during the last glacial period

Most pollen analysis in Korea has focused on the Holocene Epoch, because pre-last glacial maximum terrestrial archives suitable for palynological study in the Korean Peninsula are limited. Thus, to verify the responses of vegetation to climate changes over the orbital timescales, analysis of pollen in marine sediments is needed. Here, we present the pollen record of hemipelagic sediments of core DD09-ST21 obtained from the northern Ulleung Basin in the East Sea. The palynofloral assemblages were dominated by warm temperate broadleaved trees and boreal conifers during interglacial and glacial periods, respectively. We also demonstrated that bisaccate pollen and herbaceous pollen in the palynological sequence can be used as indicators of the variation in the East Asian winter monsoon (EAWM) intensity during the last glacial period and freshwater inflow into the East Sea, respectively. During glacial periods, the EAWM intensified in response to weakening of the summer insolation at 60° N, while freshwater influx into the East Sea decreased due to a decrease in precipitation.

Early Holocene weakening and mid- to late Holocene strengthening of the East Asian winter monsoon

AbstractSub-orbital-scale variations of the East Asian winter monsoon (EAWM) and its mechanisms during the Holocene are controversial, partly due to the lack of high-quality records from Chinese loess. Here, we present high-resolution reconstruction of Holocene EAWM intensity based on optically stimulated luminescence dating and grain-size analysis from three loess sections taken from the Chinese Loess Plateau. The EAWM showed a persistent weakening trend during the early Holocene (ca. 11.7–6.5 kyr B.P.) and a strengthening trend during the mid- to late Holocene (since ca. 6.5 kyr B.P.). We propose that this was caused by changes in high-latitude Northern Hemisphere ice volume and middle- to high-latitude Northern Hemisphere atmospheric temperatures, respectively. We also observed an anti-correlation between EAWM and East Asian summer monsoon. Our findings provide a robust solution to the debate regarding Holocene EAWM changes and contribute to the understanding of potential future variations in EAWM intensity.

Quantifying the contribution of anthropogenic influence to the East Asian winter monsoon in 1960–2012

Abstract. The East Asian winter monsoon (EAWM) is greatly influenced by many factors that can be classified as anthropogenic forcing and natural forcing. Here we explore the contribution of anthropogenic influence to the change in the EAWM over the past decades. Under all forcings observed during 1960–2013 (All-Hist run), the atmospheric general circulation model is able to reproduce the climatology and variability of the EAWM-related surface air temperature and 500 hPa geopotential height and shows a statistically significant decreasing EAWM intensity with a trend coefficient of ∼-0.04 yr−1, which is close to the observed trend. By contrast, the simulation, which is driven by the same forcing as the All-Hist run but with the anthropogenic contribution to them removed, shows no decreasing trend in the EAWM intensity. By comparing the simulations under two different forcing scenarios, we further reveal that the responses of the EAWM to the anthropogenic forcing include a rise of 0.6∘ in surface air temperature over East Asia as well as weakening of the East Asian trough, which may result from the poleward expansion and intensification of the East Asian jet forced by the change in temperature gradient in the troposphere. Additionally, compared with the simulation without anthropogenic forcing, the frequency of strong (weak) EAWM occurrence is reduced (increased) by 45 % (from 0 to 10/7). These results indicate that the weakening of the EAWM during 1960–2013 may be mainly attributed to the anthropogenic influence.

Seasonal Variations in the Siliciclastic Fluxes to the Western Philippine Sea and Their Impacts on Seawater εNd Values Inferred From 1 Year of In Situ Observations Above Benham Rise

AbstractThe Sr and Nd isotopic compositions of siliciclastic sediments and the Nd isotopic compositions of planktonic foraminifera are investigated in sediment trap samples collected in 2015 at water depths of 500 and 2,800 m to (1) track the seasonal changes in the sources and transport patterns of siliciclastic sediments to Benham Rise, (2) constrain the Nd isotopic compositions of the planktonic foraminifera throughout the water column, and (3) assess the influences of lithogenic inputs on the Nd isotopic compositions of the water masses. We demonstrate that volcanic matter and eolian dust are derived primarily from Luzon Island and the Ordos Desert, respectively. In addition, we show that reduced precipitation over Luzon Island and the weakened East Asian winter monsoon intensity result in mass fluxes from Luzon Island and the eastern Asian deserts to the sea, respectively, that are weaker in the winter than in the spring. Furthermore, the εNd values of the foraminifera collected at a water depth of 500 m change slightly in 2015, suggesting negligible impacts of lithogenic Nd inputs characterized by significant seasonal flux variations. In contrast, the εNd values of the planktonic foraminifera collected at a water depth of 2,800 m are systematically more radiogenic and appear to display seasonal variability. Such results suggest the rapid modification of εNd values during the settling of planktonic foraminifera by the precipitation of Mn coatings derived from water masses at deposition depths, with greater contributions of colder water masses originating from the volcanic Luzon Island margin during the winter.

Prediction Skill for the East Asian Winter Monsoon Based on APCC Multi-Models

The prediction skill for the East Asian winter monsoon (EAWM) has been analyzed, using the observations and different climate models that participate in the APEC Climate Center (APCC) multi-model ensemble (MME) seasonal forecast. The authors first examined the characteristics of the existing EAWM indices to find a suitable index for the APCC seasonal forecast system. This examination revealed that the selected index shows reasonable prediction skill of EAWM intensity and well-represents the characteristics of wintertime temperature anomalies associated with the EAWM, especially for the extreme cold winters. Although most models capture the main characteristics of the seasonal mean circulation over East Asia reasonably well, they still suffer from difficulty in predicting the interannual variability (IAV) of the EAWM. Fortunately, the POAMA has reasonable skill in capturing the timing and strength of the EAWM IAV and reproduces the EAWM-related circulation anomalies well. The better performance of the POAMA may be attributed to the better skill in simulating the high-latitude forcing including the Siberian High (SH) and Artic Oscillation (AO) and the strong links of the ENSO to the EAWM, compared to other models.

Variations of Siberian High Position under climate change: Impacts on winter pollution over north China

We examined the correlations between winter aerosol optical depth (AOD) in North China (NC) and three synoptic-scale meteorological indices from 2001 to 2016, including the Siberian High intensity (SHI), East Asian Winter Monsoon intensity (EAWMI), and the Siberian High Position index (SHPI). To separate the influences from meteorology and emissions, NC AOD was detrended by subtracting a linear increasing trend from 2001 to 2013 and a decreasing trend from 2014 to 2016, in correspondence with reported changes in Chinese anthropogenic emissions during the same period. The SHPI explains 37% of the variability in the detrended NC AOD and 83% of the high SHPI winters correspond to high AOD. By contrast, the SHI and EAWMI show little correlation with the observed AOD variability. To project the SHPI in the future climate, we used the ensemble of six global circulation models (GCMs) which were found capable of reproducing the climatic spatial distribution and the longitudinal variability of the Siberian High from 1956 to 2005. The ensemble results show that the frequency of high SHPI winters and consequently more polluted conditions would increase by 29%, 61%, and 100% under RCP2.6, RCP4.5 and RCP8.5 until 2099. There are 11 out of the 25 GCMs examined here that project the possibility of high SHPI conditions to increase under RCP8.5. This indicates changes in the Siberian High position induced by increasing global greenhouse gas (GHG) emissions can lead to more winter pollution in North China in the future.

Middle Holocene Organic Carbon and Biomarker Records from the South Yellow Sea: Relationship to the East Asian Monsoon

The East Asian monsoon system influences the sedimentation and transport of organic matter in East Asian marginal seas that is derived from both terrestrial and marine sources. In this study, we determined organic carbon (OC) isotope values, concentrations of marine biomarkers, and levels of OC and total nitrogen (TN) in core YSC-1 from the central South Yellow Sea (SYS). Our objectives were to trace the sources of OC and variations in palaeoproductivity since the middle Holocene, and their relationships with the East Asian monsoon system. The relative contributions of terrestrial versus marine organic matter in core sediments were estimated using a two-end-member mixing model of OC isotopes. Results show that marine organic matter has been the main sediment constituent since the middle Holocene. The variation of terrestrial organic carbon concentration (OCter) is similar to the EASM history. However, the variation of marine organic carbon concentration (OCmar) is opposite to that of the EASM curve, suggesting OCmar is distinctly influenced by terrestrial material input. Inputs of terrestrial nutrients into the SYS occur in the form of fluvial and aeolian dust, while concentrations of nutrients in surface water are derived mainly from bottom water via the Yellow Sea circulation system, which is controlled by the East Asian winter monsoon (EAWM). Variations in palaeoproductivity represented by marine organic matter and biomarker records are, in general, consistent with the recent EAWM intensity studies, thus, compared with EASM, EAWM may play the main role to control the marine productivity variations in the SYS.

Mass accumulation rate changes in Chinese loess during MIS 2, and asynchrony with records from Greenland ice cores and North Pacific Ocean sediments during the Last Glacial Maximum

Abstract Sensitivity-corrected quartz optically stimulated luminescence (OSL) dating methods have been widely accepted as a promising tool for the construction of late Pleistocene chronology and mass or dust accumulation rates (MARs or DARs) on the Chinese Loess Plateau (CLP). Many quartz OSL ages covering marine isotope stage (MIS) 2 (equal to L 1-1 in Chinese loess) have been determined for individual sites within the CLP in the past decade. However, there is still a lack of detailed MAR or DAR reconstruction during MIS 2 across the whole of the CLP. Here, we present detailed MARs determined for eight sites with closely-spaced quartz OSL ages covering ∼MIS 2, and relative MARs suggested by a probability density analysis of 159 quartz OSL ages ranging from ∼30 to 10 ka ago, from 15 sites on the CLP. The results show enhanced dust accumulation during the Last Glacial Maximum (LGM), with particularly rapid dust accumulation from ∼23 to 19 ka ago (the late LGM). In contrast, MARs determined for the last deglaciation (from ∼19 to 12 ka ago) are low. The MAR changes during MIS 2 in Chinese loess are mainly controlled by the East Asian winter monsoon (EAWM) intensity, which is forced by Northern Hemisphere ice volume. The MAR changes also indicate that dust accumulation during MIS 2 is generally continuous at millennial time scales on the CLP. Comparison of Asian-sourced aeolian dust MARs in Chinese loess with those preserved in Greenland ice cores and North Pacific Ocean sediments indicates that rapid dust accumulation occurred from ∼26 to 23 ka ago (the early LGM) in Greenland ice cores and North Pacific Ocean sediments, suggesting a several kilo-year difference in timing when compared with the rapid dust accumulation during the late LGM in Chinese loess. This asynchronous timing in enhanced dust accumulation is probably related to both changes in the EAWM intensity and changes in the mean position of zone axis of the Westerly jet, both of which are greatly influenced by Northern Hemisphere ice volume. This study highlights the possible influence of changes in the mean position of zone axis of the Westerly jet on long-range transport of Asian-sourced dust.

Asynchronous variation in the East Asian winter monsoon during the Holocene

AbstractThe East Asian winter monsoon (EAWM) is one of the most active components of the global climate system. Climate anomalies associated with the EAWM differ between extratropical and tropical regions due to the EAWM's meridional extent. Spatial differences in the EAWM variability on centennial and millennial time scales during the Holocene have not been well understood. This study describes Holocene spatiotemporal features of the EAWM based on comparisons of proxy records and climate simulations. The analysis specifically compared four proxy records located throughout China to assess the EAWM's spatial variability during the Holocene. These records indicate a stronger EAWM during the early Holocene than that during the late Holocene. The EAWM also shows a rapid, asynchronous decline from northwestern to southeastern China. The EAWM declined in northwestern China from 10 to 7.5 ka B.P., whereas the decline did not occur in southern China and the eastern Tibetan Plateau until 6–4.5 ka B.P. Coupled equilibrium and transient simulations of climate evolution during the Holocene indicate that the decline of the EAWM from 10 to 7.5 ka B.P. was probably caused by melting of Northern Hemisphere (NH) ice sheets and enhanced Atlantic meridional overturning circulation (AMOC). The decline of the EAWM from 6 to 4.5 ka B.P. over the eastern Tibetan Plateau and southern China is related to an abrupt increase in sea surface temperatures (SSTs) of the tropical western Indian Ocean. We therefore argue that the regional shift in EAWM intensity was probably related to a distinguishing response to high‐latitude (NH ice sheets and AMOC) and low‐latitude (tropical SSTs) forcings.