Nam Co is the largest (1920 km2 in area) and highest (4718 m above sea level) lake in Tibet. According to the discovery of lake terraces and highstand lacustrine deposits at several places in Nam Co and its adjacent a...Nam Co is the largest (1920 km2 in area) and highest (4718 m above sea level) lake in Tibet. According to the discovery of lake terraces and highstand lacustrine deposits at several places in Nam Co and its adjacent areas, the authors confirm the existence of an ancient large lake in the southeastern part of the northern Tibetan Plateau. On the basis of the U-series, 14C and ESR dating, coupled with the levelling survey of lake deposits and geomorphology, the evolutionary process of the ancient large lake in the southeastern part of the northern Tibetan Plateau may fall into three stages: (1) the ancient large lake stage at 115-40 ka BP, when the ancient lake level was 140-26 m above the level of present Nam Co; (2) the outflow lake stage at 40-30 ka BP, when the ancient level was 26-19 m above the present lake level; and (3) the Nam Co stage since 30 ka BP, when the ancient lake level was < 19 m above the present lake level. During the ancient large lake stage, a large number of modern large, medium-sized and small lakes, including Nam Co, Siling Co and Zhari Namco, in the southeastern part of the northern Tibetan Plateau, were connected into a single large ancient lake, rather than several separate lakes connected by river channels. Its areal extent may have gone beyond the watersheds of the modern endorheic and exorheic drainage systems; so it may be called the 'ancient east lake', 'ancient south lake' and 'ancient west lake'. It might also be connected with other ancient lakes in the southern and western parts of the northern Tibetan Plateau to form a unified 'ancient large lake' on the northern Tibetan Plateau.展开更多
Mangroves,widely distributed along the coasts of tropical China,are influenced by Asia monsoon,relative sea level change and enhanced human activity.To predict the impacts of future climate change on mangrove ecosyste...Mangroves,widely distributed along the coasts of tropical China,are influenced by Asia monsoon,relative sea level change and enhanced human activity.To predict the impacts of future climate change on mangrove ecosystems,it can be understood by reconstructing past mangrove dynamics using proxies preserved in coastal sediments.In this study,we quantitatively partitioned buried organic matter(OM)sources,collected from a vulnerable mangrove swamp in the Qinzhou Bay of northwestern South China Sea,using a ternary end-member mixing model of δ^13C and C:N values.Mangrove-derived OM(MOM)contribution was used as a tracer for mangrove development since 2.34 cal ka BP.This information,together with paleoclimate records(i.e.,speleothem δ^18O values,sea level change,grain size parameters)and human activity,was used to divide mangrove development into three stages during the late Holocene:relative flourish(2.34-1.13 cal ka BP),relative degradation(1.13-0.15 cal ka BP)and further degradation(0.15-0 cal ka BP).Before 1.13 cal ka BP,mangroves flourished with a high MOM contribution((88.9±10.6)%),corresponding to stable and high sea level under a warm and humid climate.After 1.13 cal ka BP,rapid fall in relative sea level coupled with the strengthening of the Asian winter monsoon,resulted in mangrove degradation and MOM reduction((62.4±18.9)%).Compared with air temperature and precipitation,the relative sea level fall was the main controlling factor in mangrove development before entering the Anthropocene(the time of the Industrial Revolution).After^150 cal a BP,reclamation of mangrove swamps to shrimp ponds is the main factor causing mangrove degradation and MOM reduction.展开更多
文摘Nam Co is the largest (1920 km2 in area) and highest (4718 m above sea level) lake in Tibet. According to the discovery of lake terraces and highstand lacustrine deposits at several places in Nam Co and its adjacent areas, the authors confirm the existence of an ancient large lake in the southeastern part of the northern Tibetan Plateau. On the basis of the U-series, 14C and ESR dating, coupled with the levelling survey of lake deposits and geomorphology, the evolutionary process of the ancient large lake in the southeastern part of the northern Tibetan Plateau may fall into three stages: (1) the ancient large lake stage at 115-40 ka BP, when the ancient lake level was 140-26 m above the level of present Nam Co; (2) the outflow lake stage at 40-30 ka BP, when the ancient level was 26-19 m above the present lake level; and (3) the Nam Co stage since 30 ka BP, when the ancient lake level was < 19 m above the present lake level. During the ancient large lake stage, a large number of modern large, medium-sized and small lakes, including Nam Co, Siling Co and Zhari Namco, in the southeastern part of the northern Tibetan Plateau, were connected into a single large ancient lake, rather than several separate lakes connected by river channels. Its areal extent may have gone beyond the watersheds of the modern endorheic and exorheic drainage systems; so it may be called the 'ancient east lake', 'ancient south lake' and 'ancient west lake'. It might also be connected with other ancient lakes in the southern and western parts of the northern Tibetan Plateau to form a unified 'ancient large lake' on the northern Tibetan Plateau.
基金The National Natural Science Foundation of China under contract Nos 41576067 and 41576061the Basic Scientific Fund for National Public Research Institutes of China under contract No.2017Q03the National Basic Research Program(973Program)of China under contract No.2010CB951203
文摘Mangroves,widely distributed along the coasts of tropical China,are influenced by Asia monsoon,relative sea level change and enhanced human activity.To predict the impacts of future climate change on mangrove ecosystems,it can be understood by reconstructing past mangrove dynamics using proxies preserved in coastal sediments.In this study,we quantitatively partitioned buried organic matter(OM)sources,collected from a vulnerable mangrove swamp in the Qinzhou Bay of northwestern South China Sea,using a ternary end-member mixing model of δ^13C and C:N values.Mangrove-derived OM(MOM)contribution was used as a tracer for mangrove development since 2.34 cal ka BP.This information,together with paleoclimate records(i.e.,speleothem δ^18O values,sea level change,grain size parameters)and human activity,was used to divide mangrove development into three stages during the late Holocene:relative flourish(2.34-1.13 cal ka BP),relative degradation(1.13-0.15 cal ka BP)and further degradation(0.15-0 cal ka BP).Before 1.13 cal ka BP,mangroves flourished with a high MOM contribution((88.9±10.6)%),corresponding to stable and high sea level under a warm and humid climate.After 1.13 cal ka BP,rapid fall in relative sea level coupled with the strengthening of the Asian winter monsoon,resulted in mangrove degradation and MOM reduction((62.4±18.9)%).Compared with air temperature and precipitation,the relative sea level fall was the main controlling factor in mangrove development before entering the Anthropocene(the time of the Industrial Revolution).After^150 cal a BP,reclamation of mangrove swamps to shrimp ponds is the main factor causing mangrove degradation and MOM reduction.
