Although the mid-late Holocene cold and dry event about 4000years ago （the 4ka event） has been observed almost globally, it was most prominent in terrestrial climate proxies from the lower latitudes. Here we evaluat...Although the mid-late Holocene cold and dry event about 4000years ago （the 4ka event） has been observed almost globally, it was most prominent in terrestrial climate proxies from the lower latitudes. Here we evaluate the oceanic response to this event in terms of a Holocene sea surface temperature （SST） record reconstructed using the U^7 index for Core B3 on the continen- tal shelf of the East China Sea. The record reveals a large temperature drop of about 5~C from the mid-Holocene （24.7~C at 5.6ka） to the 4ka event （19.2~C at 3.8ka）. This mid-late Holocene cooling period in Core B3 correlated with （i） decreases in the East Asia summer monsoon intensity and （ii） the transition period with increased E1 Nifio/Southern Oscillation activities in the Equatorial Pa- cific. Our SST record provides oceanic evidence for a more global nature of the mid-late Holocene climate change, which was most likely caused by a southward migration of the Intertropical Converge Zone in response to the decreasing summer solar insolation in the Northern Hemisphere. However, the large SST drop around Core B3 indicates that the mid-late Holocene cooling was regionally amplified by the initiation/strengthening of eddy circulation/cold front which caused upwelling and resulted in additional SST de- crease. Upwelling during the mid-late Holocene also enhanced with surface productivity in the East China Sea as reflected by higher alkenone content around Core B3.展开更多
As an important marginal sea under the influences of both the Changjiang River and the Kuroshio, the East China Sea （ECS） environment is sensitive to both continental and oceanic forcing. Paleoenvironmental records ...As an important marginal sea under the influences of both the Changjiang River and the Kuroshio, the East China Sea （ECS） environment is sensitive to both continental and oceanic forcing. Paleoenvironmental records are essential for understanding the long-term environmental evolution of the ECS and adjacent areas. However, paleo-temperature records from the ECS shelf are currently very limited. In this study, the U^K_37 and TEX86 paleothermometers were used to reconstruct surface and subsurface temperature changes of the mud area southwest of the Cheju Island （Site F10B） in the ECS during the Holocene. The results indicate that temperature changes of F 10B during the early Holocene （11.6-6.2 kyr） are associated with global climate change. During the period of 6.2-2.5 kyr, the similar variability trends of smoothing average of AT （the difference between surface and subsurface temperature） of Site F10B and the strength of the Kuroshio suggest that the Kuroshio influence on the site started around 6.2kyr when the Kuroshio entered the Yellow Sea and continued to 2.5 kyr. During the late Holocene （2.5-1.45 kyr）, apparent decreases of U^K_37 sea surface temperature （SST） and AT imply that the direct influence of the Kuroshio was reduced while cold eddy induced by the Kuroshio gradually controlled hydrological conditions of this region around 2.5 kyr.展开更多
基金supported by the National Basic Research Program of China (973 Program 2010CB428901)the Natural Science Foundation of China (Grant Nos. 41221004 and 41020164005)
文摘Although the mid-late Holocene cold and dry event about 4000years ago （the 4ka event） has been observed almost globally, it was most prominent in terrestrial climate proxies from the lower latitudes. Here we evaluate the oceanic response to this event in terms of a Holocene sea surface temperature （SST） record reconstructed using the U^7 index for Core B3 on the continen- tal shelf of the East China Sea. The record reveals a large temperature drop of about 5~C from the mid-Holocene （24.7~C at 5.6ka） to the 4ka event （19.2~C at 3.8ka）. This mid-late Holocene cooling period in Core B3 correlated with （i） decreases in the East Asia summer monsoon intensity and （ii） the transition period with increased E1 Nifio/Southern Oscillation activities in the Equatorial Pa- cific. Our SST record provides oceanic evidence for a more global nature of the mid-late Holocene climate change, which was most likely caused by a southward migration of the Intertropical Converge Zone in response to the decreasing summer solar insolation in the Northern Hemisphere. However, the large SST drop around Core B3 indicates that the mid-late Holocene cooling was regionally amplified by the initiation/strengthening of eddy circulation/cold front which caused upwelling and resulted in additional SST de- crease. Upwelling during the mid-late Holocene also enhanced with surface productivity in the East China Sea as reflected by higher alkenone content around Core B3.
基金supported by the National Basic Research Program of China(973 Program 2010CB428901)the National Natural Science Foundation of China(Grant Nos.41221004,41276068)the ‘111’ Project
文摘As an important marginal sea under the influences of both the Changjiang River and the Kuroshio, the East China Sea （ECS） environment is sensitive to both continental and oceanic forcing. Paleoenvironmental records are essential for understanding the long-term environmental evolution of the ECS and adjacent areas. However, paleo-temperature records from the ECS shelf are currently very limited. In this study, the U^K_37 and TEX86 paleothermometers were used to reconstruct surface and subsurface temperature changes of the mud area southwest of the Cheju Island （Site F10B） in the ECS during the Holocene. The results indicate that temperature changes of F 10B during the early Holocene （11.6-6.2 kyr） are associated with global climate change. During the period of 6.2-2.5 kyr, the similar variability trends of smoothing average of AT （the difference between surface and subsurface temperature） of Site F10B and the strength of the Kuroshio suggest that the Kuroshio influence on the site started around 6.2kyr when the Kuroshio entered the Yellow Sea and continued to 2.5 kyr. During the late Holocene （2.5-1.45 kyr）, apparent decreases of U^K_37 sea surface temperature （SST） and AT imply that the direct influence of the Kuroshio was reduced while cold eddy induced by the Kuroshio gradually controlled hydrological conditions of this region around 2.5 kyr.
