RESUMO
The normalized difference vegetation index (NDVI) is widely used in various fields of vegetation research. Due to the short observation time, however, it is difficult to meet the research needs at long time scale. Here, we established a tree-ring width chronology (STD) based on Picea schrenkiana in Bayinbuluke, and calculated the correlation coefficient of chronology and NDVI with meteorological data. The results showed that both tree-ring width index and NDVI were significantly correlated with meteorological data. Combined with the significant positive correlation between width chronology and NDVI in June-August (r=0.7, P<0.01, n=38), summer NDVI (from June to August) was reconstructed over the past 339 years using a regression model. During 1680-2018, the reconstruction series had four dense vegetation periods (1738-1765, 1786-1798, 1964-1973 and 2000-2018) and five sparse vegetation periods (1690-1714, 1825-1834, 1850-1880, 1895-1920 and 1945-1955). The reconstruction reflected the hydrological signals in the central Tianshan Mountains. The comparison with the surrounding reconstructions revealed that when the runoff of Kaidu River increased and the local environment was humid, the vegetation coverage was high; otherwise the vegetation coverage was low. The extreme value of the reconstruction series also captured a series of natural disasters recorded in historical documents. Results of HYSPLT (Hybrid Single-Particle Lagrangian Integrated Trajectory Model) backward trajectory model and wind field analysis showed that NDVI anomalies were affected by the precipitation from Westerlies.
Assuntos
Picea , Árvores , China , Mudança Climática , Estações do AnoRESUMO
Knowledge of spatial and temporal hydroclimatic differences is critical in understanding climatic mechanisms. Here we show striking hydroclimatic contrasts between northern and southern parts of the eastern margin of the Tibetan Plateau (ETP), and those between East Asian summer monsoon (EASM) and Indian summer monsoon (ISM) areas during the past ~2,000 years. During the Medieval Period, and the last 100 to 200 years, the southern ETP (S-ETP) area was generally dry (on average), while the northern ETP (N-ETP) area was wet. During the Little Ice Age (LIA), hydroclimate over S-ETP areas was wet, while that over N-ETP area was dry (on average). Such hydroclimatic contrasts can be broadly extended to ISM and EASM areas. We contend that changes in sea surface temperatures (SSTs) of the tropical Pacific Ocean could have played important roles in producing these hydroclimatic contrasts, by forcing the north-south movement of the Intertropical Convergence Zone (ITCZ) and intensification/slowdown of Walker circulation. The results of sensitivity experiments also support such a proposition.
RESUMO
Knowledge of peatland development over the tropical/subtropical zone during the last glaciation is critical for understanding the glacial global methane cycle. Here we present a well-dated 'peat deposit-lake sediment' alternate sequence at Tengchong, southwestern China, and discuss the peatland development and its linkage to the global glacial methane cycle. Peat layers were formed during the cold Marine Isotope Stage (MIS)-2 and -4, whereas lake sediments coincided with the relatively warm MIS-3, which is possibly related to the orbital/suborbital variations in both temperature and Asian summer monsoon intensity. The Tengchong peatland formation pattern is broadly synchronous with those over subtropical southern China and other tropical/subtropical areas, but it is clearly in contrast to those over the mid-high Northern Hemisphere. The results of this work suggest that the shifts of peatland development between the tropical/subtropical zone and mid-high Northern Hemisphere may have played important roles in the glacial/interglacial global atmospheric CH4 cycles.
