海洋地质与环境重点实验室知识库

The scarcity of modern observational data hampers the understanding of inter-annual to centennial climate variability in historical period and the accurate prediction of future climate change. Besides, the sufficiently long and high temporal resolution proxies over the past two millennia are very deficient, and results of temperature and precipitation reconstructions over the past two millennia are still controversial. Northeastern Taiwan and its adjacent sea area is intersection of the circulation in northern high latitudes and the circulation in tropical Pacific. Thus, the variability of  hydroclimate in this area is very sensitive to the high- low latitudes’ climate change. In this thesis, modern observation data and TOC%, TOC/TN, δ¹³C_org, grain-size, carbonate content of the MD05-2907, which was collected from the sea area offshore northeastern Taiwan, were used to analyze the multiple-time-scales climate variability in the northeastern Taiwan and its adjacent sea area, and reveal the seasonal and inter-annual anomalies of sea surface temperature(SST) offshore northeastern Taiwan and its influence factors in recent warm period, and discuss the process of inter-annual to centennial precipitation changes in the northeastern Taiwan over the past two millennia and its potential control mechanisms. Main conclusions of this thesis are outlined as follows:
(1) Seasonal and inter-annual anomalies of SST offshore northeastern Taiwan and its link to East Asian Winter Monsoon(EAWM) and El Niño-Southern Oscillation (ENSO). Based on NOAA's monthly sea surface temperature data, monthly SST data from Hadley Center and monthly Multivariate ENSO Index (MEI), the seasonal and inter-annual anomalies of SST and their influencing factors offshore northeastern Taiwan under the background of modern global warming are analyzed in order to further understand modern global warming and historical climate changes. On seasonal timescales, winter SST always display greater variation range than summer SST, and its influence on the annual mean SST and SST seasonality is more serious, which could be contributed to the effects of EAWM. Modern instrumental data and paleoclimate records show that greater variabilities of winter SST than summer SST possibly also exist on the inter-annual to centennial scale. On inter-annual timescales, the SST anomalies offshore northeastern Taiwan exhibit a significant link to ENSO. It is crucial to distinguish the different multi-scales of climate change and seasonal explanations of temperature proxies when reconstructing the past temperature variation. And, insight to the responses of historical climate to ENSO and EAWM would be helpful to further understand the cause of modern global warming.
(2) The suess effect in the δ¹³C_org record of marine sediments offshore northeastern Taiwan. The δ¹³C_org record of MD05-2907 offshore northeastern Taiwan shows that the δ¹³C_org values of marine sediments had a rapid negative shift since the end of 19 century, and the rate of this negative shift never happened over the past two millennia. This phenomenon had a close relationship with human activities- induced suess effect. The atmospheric CO₂ concentration sharply raised and the δ¹³C in atmospheric CO₂ significantly changed since the industrial revolution as a result of combustion of fossil fuels. The suess effect in the δ¹³C_org record of MD05-2907 offshore northeastern Taiwan substantiates a strong influence of human activities on the organic carbon isotopic composition in marine sediments.
(3) Characteristics of precipitation changes in the northeastern Taiwan over the past two millennia. This study reconstructed precipitation changes in the northeastern Taiwan over the past two millennia using multiple proxies(TOC%, TOC/TN, δ¹³C_org, grain-size, carbonate content and their PC1) as precipitation indicators. Our results show that this region received more precipitation during the Dark Ages Cold Period(DACP, AD 500-800) and Current Warm Period(CWP, AD 1850-2005), and less precipitation during the Roman Warm Period(RWP, AD 0-300), Medieval Climate Anomaly(MCA, AD1000-1300) and Little Ice Age(LIA, AD 1400-1700). On the inter-annual to centennial scale, the precipitation in this region was significantly influenced by solar irradiance, ENSO/PDO and NAO. In the DACP, this region received more precipitation owing to the stronger decadal tropical Pacific variability(ENSO/PDO) and stronger Walker circulation. In the LIA, this region received significantly lessprecipitation due to the weaker solar irradiance and stronger North Atlantic circulation anomalies(NAO).