中全新世以来南黄海岩心记录的沉积环境演变对东亚季风的响应

对南黄海中部泥质沉积区中心位置的Z1钻孔进行了AMSMC年龄、粒度和TOC／TN分析，综合指标结果揭示了中晚全新世以来南黄海区域的沉积环境演化。自6094aBP以来，沉积速率、平均粒径和TOC／TN整体趋势的减少指示，研究区陆源物质输入的减少与东亚冬／夏季风的减弱有关。根据粒度参数和TOC／TN变化将研究区沉积环境演化分成3个阶段：①6．1～5．4kaBP时沉积物粒度最粗，TOC／TN值较高，这与该阶段东亚冬季风的强盛且稳定和黄海暖流的形成初期较弱有关；②5．4～3．9kaBP时沉积物粒度减小但波动幅度较大，TOC／TN值呈减小趋势，此阶段东亚冬季风减弱但波动剧烈；③3．9～0kaBP时沉积物粒度较细且相对稳定，TOC／TN增加直至趋于稳定，该阶段冬季风减至最弱且趋于稳定。另外岩心记录的6．0、5．3、4．6、4．0和3．4kaBP沉积物粒度明显较粗、TOC／TN值较大与东亚冬季风增强、海区温度较低有关；6．1～5．7kaBP的高速沉积与冬季风强盛有关；2．8～1．9kaBP的高速沉积则与黄海沿岸流和黄海暖流共同作用形成的南黄海中部气旋式冷涡的加强稳固有关。

Long-term variabilities of thermodynamic structure of the East China Sea Cold Eddy in summer

Based on more than 30 years observed sectional temperature data since the 1960s, and compared with multi-year wind and Changjiang (Yangtze) River discharge data, spatial-temporal variations of the East China Sea Cold Eddy (ECSCE) in summer was analyzed in relationship to ocean circulation and local atmospheric circulation. Empirical Orthogonal Function (EOF) and Singular Value Decomposition (SVD) analyses were applied to this study. The results show that: 1) The ECSCE in summer possesses significant interannual variabilities, which are directly associated with oceanic and atmospheric circulation anomaly. Main fluctuations demonstrate their falling in basically with El Nino events (interannual) and interdecadal variability. 2) The ECSCE in summer is closely related to the variation of the Yellow Sea Warm Current (YSWC) and the Changjiang River discharge. The stronger the YSWC, the more intensive the ECSCE with its center shifting westward,and vice versa. However, a negative correlation between the Changjiang River discharge and the ECSCE strength is shown. The ECSCE was strengthened after the abrupt global climate change affected by the interdecadal variation of the YSWC. 3) SVD analysis suggested a high correlation between the variation of the ECSCE in summer and the anomalous cyclonic atmospheric circulation over the ECS. Intensification of the cyclonic wind strengthens the ECSCE, and vice versa. 4) The cyclonic atmospheric circulation has dominant influence on the interannual variation of the ECSCE, and the infltience of the ocean circulation takes the second in. The ECSCE was usually stronger in El Nino years affected by strong cyclonic circulation in the atmosphere. The variation in strength of the ECSCE resulted from the joint effect of both oceanic and atmospheric circulation.

The inter-annual variability of the Yellow Sea Warm Current surface axis and its influencing factors

Based on the Pathfinder sea surface temperature(PFSST),the surface axis and its pattern of the Yellow Sea Warm Current(YSWC) are discussed.A structure of double-warm-tongue is found in February and it varies in different years.Two indexes are calculated to represent the westward shift(WSI) and northward extension(NEI) of the warm water in the Yellow Sea(YS).Wavelet analysis illustrates that the WSI and NEI have prominent periods of 3-6 years and 3-4 years,respectively.The Empirical Orthogonal Function(EOF) decomposition is applied to the winter wind stress curl and the Kuroshio Current(KC) transport,which are believed to play important roles in forcing the variability of the YSWC surface axis.Statistics shows that the WSI is significantly related with the second EOF mode of the wind stress curl in February,which may force the YSWC surface axis moving westward and maintaining the double warm tongues because of its opposite curl in the YSWC domain.The first EOF mode of wind stress curl in January is propitious for inducing the warm tongue in the YS to advance more northward.Hence,the wind stress curls both in January and in February could force variations of the YSWC surface axis;however,the effect of the January wind stress curl is relatively weaker than that of the February.The relationship between the NEI and the KC transport is remarkable,and it seems that the stronger KC supplies more power to push the YSWC northward against the southward wind.

Case analysis of water exchange between the Bohai and Yellow Seas in response to high winds in winter

Based on the data from a special project titled China's Offshore Marine Integrated Investigation and Evaluation as well as Regional Ocean Modeling Systems(ROMS)diagnostic numerical model,we studied the influence of high wind processes on the circulation and water exchange between the Bohai and Yellow Seas(BYS)in winter.The results show that the vertical structure of the Yellow Sea Warm Current(YSWC)is relatively uniform under condition of high winds,showing obvious barotropic features.However,this flow is not a stable mean flow,showing strong paroxysmal and reciprocating characteristics.A comparison of the changes in sea level suggests that the intensity of the northwards upwind flow is consistent with the abnormal fluctuations in the sea level.It indicates that the upwind flow is closely related to the water exchange between the BYS.The impact of high wind processes on the water exchange between the BYS is enormous.It can make the flux through the Bohai Strait,as well as that through the mouth of each constituent bay(i.e.,Liaodong Bay,Bohai Bay,and Laizhou Bay)far greater than usual,resulting in a significant increase in the water exchange rate.The exchange capacity,which is about 8%of the total volume of the Bohai Sea,can be completed in a few days.Therefore,the water exchange of the Bohai Sea may be completed by only a few occasional high wind processes in winter.

An N-shape thermal front in the western South Yellow Sea in winter

An N-shape thermal front in the western South Yellow Sea (YS) in winter was detected using Advanced Very High Resolution Radiation (AVHRR) Sea Surface Temperature data and in-situ observations with a merged front-detecting method.The front,which exists from late October through early March,consists of western and eastern wings extending roughly along the northeast-southwest isobaths with a southeastward middle segment across the 20-50 m isobaths.There are north and south inflexions connecting the middle segment with the western and eastern wings,respectively.The middle segment gradually moves southwestward from November through February with its length increasing from 62 km to 107 km and the southern inflexion moving from 36.2°N to 35.3°N.A cold tongue is found to coexist with the N-shape front,and is carried by the coastal jet penetrating southward from the tip of the Shandong Peninsula into the western South YS as revealed by a numerical simulation.After departing from the coast,the jet flows as an anti-cyclonic recirculation below 10 m depth,trapping warmer water originally carried by the compensating Yellow Sea Warm Current (YSWC).A northwestward flowing branch of the YSWC is also found on the lowest level south of the front.The N-shape front initially forms between the cold tongue and warm water involved in the subsurface anti-cyclonical recirculation and extends upwards to the surface through vertical advection and mixing.Correlation analyses reveal that northerly and easterly winds tend to be favorable to the formation and extension of the N-shape front probably through strengthening of the coastal jet and shifting the YSWC pathway eastward,respectively.

Seasonality and causes of the Yellow Sea Warm Current

To study the seasonality and causes of the Yellow Sea Warm Current (YSWC) in detail, rotated empirical orthogonal function (REOF) and extended associate pattern analysis are adopted with daily sea surface salinity (SSS), sea surface temperature (SST) and sea surface height (SSH) datasets covering 1126 days from American Navy Experimental Real-Time East Asian Seas Ocean Nowcast System in the present paper. Results show that in the Yellow and East China Seas, the YSWC is a mean barotropic flow as compensation of winter-monsoon-driven surface currents, which has been directly observed. When East Asia winter monsoon weakens, so do the meridional pressure gradient of the surface seawater and the YSWC, while the transversal pressure gradient changes rather slowly that results in the YSWC left turning. In addition, there is southward mean flow compensation of summer-monsoon-driven surface currents, which actually was also directly observed.

A NUMERICAL STUDY ON THE PATH AND ORIGIN OF THE YELLOW SEA WARM CURRENT (YSWC)

A three dimensional baroclinic model (POM) is employed to study the path, orgin and strength of the Yellow Sea Warm Current (YSWC). The model produced results are compared with the observed temperature and salinity fields, the trajectories of drifters and moored current meter data. The results show: (1) It is indicated for the first time that the YSWC in winter orignates from the middle sector (28°N, 126°E), the truning directional sector (30°N, 127°E) of the Kuroshio in the East China Sea (ECS) and the separated sector of the Tsushima Warm Current (TsWC) at (31°N, 128°E), while in summer mainly originates from the Taiwan Warm Current (TaWC) and partly from the separated sector of the TsWC. This path is consistent with the main distribution feature of the quasi synoptic observed temperature and salinity. The model produced anticyclonic gyre (28°N, 125.5°E) branched from the middle sector of the ECS Kuroshio agrees with the observed results of the satellite drifters. (2) The model produced YSWC is located between 50～60m isobath on the West Side of the Yellow Sea Trough (YST), which is consistent with the location of the Warm and Saline tongue. The model produced cyclonic gyre centering at (36°N, 124.5°E) coincides with the observed results in Feb. 1997. The traditional view indicates that the Northern Jiangsu Coastal Current (NJCC) turns eastward at (32.5°N, 122°E). However, we think that the NJCC goes southward and only the coastal water invades near (32.5°N, 122°E). The model produced path is consistent with the warm tongue in the range of 34° 35°N, 122.5° 123.5°E in 30m layer. (3) The model produced YSWC is strong in winter and weak in summer, which coincides with the observations. The northward volume transport along 35°N section in winter and summer are 0.72sv and 0.38sv, respectively, with an annual flux of about 1.54·10 13 m 3. The volume transport entering the Bohai Sea in winter and summer are 0.19sv and 0.09sv, respectively, with an annual flux of about 4.37·10 12 m 3.

THE STUDY OF THE YELLOW SEA WARM CURRENT AND ITS SEASONAL VARIABILITY

The Yellow Sea Warm Current （YSWC） penetrates northward along the Yellow Sea Trough, and brings warm and saline water towards the Bohai Sea. The YSWC becomes much less intrusive in summer and is limited mostly in the southern trough, contrasting with a deep winter penetration well into the trough. The seasonal variability of the YSWC has prompted a debate regarding which controls the YSWC and its seasonal variability. In this article, the annual mean and seasonal variability of the YSWC was examined by using a 3-D ocean model together with several experiments. The results show that in the annual mean the YSWC is a compensating current firstly for the southward Korea Coastal Current （KCC）, which is mainly caused by the Kuroshio Current （KC）. The local wind-stress forcing plays an important but secondary role. However, the local monsoonal forcing plays a prominent role in modulating the seasonal variability. A deep northwestward intrusion of the YSWC in winter, for instance, is mainly due to a robustly developed China Coastal Current （CCC） which draws water along the Yellow Sea trough to feed a southward flow all the way from the Bohai Sea to the Taiwan Strait.

Existence, morphology and structure of the Yellow Sea Warm Current Branch approaching waters offshore Qingdao, China

In this study, we focused on full-region cruise survey data, near-bottom continuous mooring observations and sea surface wind products from the western South Yellow Sea in winter; after ensuring the data reliability and accuracy, we processed and analyzed the data. Image resolution experiments were carried out to determine the lowest recognition resolutions for all image types, which represent the resolution characteristics of the data. The existence of a warm water tongue originating from the Yellow Sea Warm Current(YSWC) that approached waters offshore Qingdao was confirmed. For the first time, a high salinity water tongue, corresponding to the warm water tongue, was described and found to be more representative of the YSWC branch path. This warm tongue is a sign of the branch originating from the YSWC, which we defined as the Yellow Sea Warm Current Branch approaching waters offshore Qingdao(YSWC-QDB). The pattern of the warm and salty water tongues showed remarkable rear, branching middle, shrinking neck and expanding top regions. These patterns showed a temporal feature of the tongues, and were the result of multi-temporal branches in front of the YSWC main section as well as the YSWC-QDB crossing the southwestward path of the extension of the North Shandong Coastal Current flowing along the southeast coast of the Shandong Peninsula(NSCC-SESE). Analysis using mooring data at a sensitive and representative station also showed the existence of the YSWC-QDB. It is a probabilistic event that manifests as a northwestward flow that decreases gradually from the bottom to the surface in the early cold air transit stage and consistent in the whole water column profile in the later stage. It varies quasi-periodically with weather processes. It also transports some of the YSWC water stored in the entrance area of the Bohai and Yellow seas under winter wind conditions to the western South Yellow Sea as a compensatory current. This current, caused by northerly winds, especially northwest winds and obstruction of the NSCC-SESE, was present, and strong water reduction and compensation caused significant residual sea level oscillations. The compensatory current, if caused by strong northwest wind,began to appear when its direction was opposite to the wind direction. In addition, confirmation of the YSWC-QDB provides an oceanographic basis for the short cooling time and rapid warming in the Qingdao area in winter. This research provides a basis for further studies of the YSWC-QDB at high spatial and temporal resolutions using large sea surface datasets. For monsoon basin dynamics, this study can also be extended to the whole Bohai and Yellow seas and closed or semi-closed basins on the continental margin.