The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon is...The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller G. ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40―24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and north- ern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima cur- rent primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle.展开更多
Results from sediment trap experiments conducted in the southern South China Sea from May 2004 to March 2006 revealed significant monsoon-induced seasonal variations in flux and shell geochemistry of planktonic forami...Results from sediment trap experiments conducted in the southern South China Sea from May 2004 to March 2006 revealed significant monsoon-induced seasonal variations in flux and shell geochemistry of planktonic foraminifera. The total and species-specific fluxes showed bimodal pattern, such as those of Globigerinoides ruber, Globigerinoides sacculifer, Neoglobo-quadrina dutertrei, Globigerinita glutinata, and Globigerina bulloides. Their high values occurred in the prevailing periods of the northeast and southwest monsoons, and the low ones appeared between the monsoons. Pulleniatina obliquiloculata had high flux rates mainly during northeast monsoon, with exceptional appearance in August 2004. These fluxes changed largely in accord with those of total particle matter and organic carbon, following chlorophyll concentration and wind force. It is inferred that the biogenic particle fluxes are controlled essentially by primary productivity under the influence of East Asian monsoon in the southern SCS. Shell stable oxygen isotope and Mg/Ca data correspond with seasonal variation of sea surface temperature. Shell δ18O values are affected primarily by sea water temperature, and the δ18O changes of different-depth dwelling species indicate upper sea water temperature gradient. Besides, the low carbon isotope values occurred in the periods of East Asian monsoon in general, whereas the high ones between the monsoons. The pattern is in contrary to chlorophyll concentration change, which indicates that the variation of the carbon isotope could probably reflect the change of sea surface productivity.展开更多
As one of the mélanges in the southern side of the Yarlung-Zangbo suture zone, the Saiqu mélange in southern Tibet is important for understanding the evolution of the Neo-Tethys ocean. The age of the Saiqu m...As one of the mélanges in the southern side of the Yarlung-Zangbo suture zone, the Saiqu mélange in southern Tibet is important for understanding the evolution of the Neo-Tethys ocean. The age of the Saiqu mélange, however, has been debated due to the lack of reliable fossil evidence in matrix strata. Based on lithological similarities with platform strata in southern Tibet and limited fossils from exotic blocks, previous studies variously ascribed the Saiqu mélange to be Triassic in general, Late Triassic, or Late Cretaceous. Here we reported planktonic foraminiferal faunas from the matrix strata of the Saiqu mélange. The new fossils yield a Late Cretaceous age, which is so far the best age constraint for the mélange. Regional stratigraphic correlation indicates that the Cretaceous Oceanic Red Beds （CORBs） in Saiqu may be time equivalent to the CORBs of the Zongzhuo Formation in neighboring regions. Thus the Saiqu m^lange should be correlated to the Upper Cretaceous Zongzhuo Formation rather than the Triassic Xiukang Group, as previously suggested.展开更多
Two hteh resolution down-cores (92-255, 92-170) are used to study the Palaxeanographic events of the southern Okinawa Trough during the last 20 000 years. Planktonic foraminifera are quantitatively analyzed and three ...Two hteh resolution down-cores (92-255, 92-170) are used to study the Palaxeanographic events of the southern Okinawa Trough during the last 20 000 years. Planktonic foraminifera are quantitatively analyzed and three paleoceanographic events are recognized. Glacial/post-glacial variations in sea surface temperature (SST), water masses and upper water column structure are the most important environmental changes recorded by planktonic foraminifera. There is also an abrupt climatic event (about 10 710~ 9 170 a BP) during the Termination I, planktonic foraminifera (PF) δ18 O and SST have a same return pattern, but benthic foraminifera (BF) δ18 O doesn' t have.therepancy between PF δ18 O and BF δ18 O may reflect that the sea suriace water is more sensitive to abrupt, short term environmental change than the sea bottom water. High-resolution strata aIso suggest a middle- Holocene Pulleniatina obliquifoculata minimum event.展开更多
基金Supported by the CAS Pilot Project of the National Knowledge Innovation Program (Project No. KZCFX3-SW-233)the National Natural Science Foundation of China (Grant Nos. 90411014 and 40506015)+1 种基金International Cooperation Projects of Ministry of Science and Technology of China (Project No. 2002DFG00034)Sino-French Joint Research Project (Project No. 40421150011)
文摘The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller G. ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40―24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and north- ern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima cur- rent primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle.
基金supported by National Key Development Program for Fundamental Research (Grant No.2007CB815901)National Natural Science Foundation of China (Grant No.40621063)
文摘Results from sediment trap experiments conducted in the southern South China Sea from May 2004 to March 2006 revealed significant monsoon-induced seasonal variations in flux and shell geochemistry of planktonic foraminifera. The total and species-specific fluxes showed bimodal pattern, such as those of Globigerinoides ruber, Globigerinoides sacculifer, Neoglobo-quadrina dutertrei, Globigerinita glutinata, and Globigerina bulloides. Their high values occurred in the prevailing periods of the northeast and southwest monsoons, and the low ones appeared between the monsoons. Pulleniatina obliquiloculata had high flux rates mainly during northeast monsoon, with exceptional appearance in August 2004. These fluxes changed largely in accord with those of total particle matter and organic carbon, following chlorophyll concentration and wind force. It is inferred that the biogenic particle fluxes are controlled essentially by primary productivity under the influence of East Asian monsoon in the southern SCS. Shell stable oxygen isotope and Mg/Ca data correspond with seasonal variation of sea surface temperature. Shell δ18O values are affected primarily by sea water temperature, and the δ18O changes of different-depth dwelling species indicate upper sea water temperature gradient. Besides, the low carbon isotope values occurred in the periods of East Asian monsoon in general, whereas the high ones between the monsoons. The pattern is in contrary to chlorophyll concentration change, which indicates that the variation of the carbon isotope could probably reflect the change of sea surface productivity.
基金financially supported by the National Basic Research Program of China(973 Program,Grant No.2006CB701400)the Project of the Geological Survey of China(Grant Nos.H45C004004,G45C001004)the National Natural Science Foundation of China(Grant No.40472011).
文摘As one of the mélanges in the southern side of the Yarlung-Zangbo suture zone, the Saiqu mélange in southern Tibet is important for understanding the evolution of the Neo-Tethys ocean. The age of the Saiqu mélange, however, has been debated due to the lack of reliable fossil evidence in matrix strata. Based on lithological similarities with platform strata in southern Tibet and limited fossils from exotic blocks, previous studies variously ascribed the Saiqu mélange to be Triassic in general, Late Triassic, or Late Cretaceous. Here we reported planktonic foraminiferal faunas from the matrix strata of the Saiqu mélange. The new fossils yield a Late Cretaceous age, which is so far the best age constraint for the mélange. Regional stratigraphic correlation indicates that the Cretaceous Oceanic Red Beds （CORBs） in Saiqu may be time equivalent to the CORBs of the Zongzhuo Formation in neighboring regions. Thus the Saiqu m^lange should be correlated to the Upper Cretaceous Zongzhuo Formation rather than the Triassic Xiukang Group, as previously suggested.
文摘Two hteh resolution down-cores (92-255, 92-170) are used to study the Palaxeanographic events of the southern Okinawa Trough during the last 20 000 years. Planktonic foraminifera are quantitatively analyzed and three paleoceanographic events are recognized. Glacial/post-glacial variations in sea surface temperature (SST), water masses and upper water column structure are the most important environmental changes recorded by planktonic foraminifera. There is also an abrupt climatic event (about 10 710~ 9 170 a BP) during the Termination I, planktonic foraminifera (PF) δ18 O and SST have a same return pattern, but benthic foraminifera (BF) δ18 O doesn' t have.therepancy between PF δ18 O and BF δ18 O may reflect that the sea suriace water is more sensitive to abrupt, short term environmental change than the sea bottom water. High-resolution strata aIso suggest a middle- Holocene Pulleniatina obliquifoculata minimum event.
