冰芯与其它记录所揭示的中国全新世大暖期变化特征

Climatic Differences in China during the Holocene Indicated by the Various Climatic Proxy Data from Different Parts of China

冰芯、孢粉、黄土、湖泊和海平面变化记录揭示出 ,在全新世时 ,我国曾发生过多次气候冷暖波动事件 ,其中最重要的事件是全新世大暖期 .由于青藏高原的存在 ,造成了中亚地区大气环流的改变 ,形成了中国大陆复杂的气候条件和独特的季风气候 ,从而导致全国各地大暖期在起讫时间、变化幅度和持续时间上都存在着较大的差异 .中国西部高海拔地区大暖期起讫时间较早、持续时间较短、变化幅度较大 ;反之 ,在中国东部 ,大暖期起讫时间较晚、持续时间较长、变化幅度较小 ,反映出西部高海拔区域对气候变化的响应度和敏感度都比东部低海拔区域强 .此外 ,不同区域的冰芯记录也有差异 ,古里雅冰芯记录反映了全球气候变化的趋势 ,而敦德冰芯记录则与我国季风气候变化的趋势比较接近 .

For a better understanding of climatic variations in China during the Holocene, climatic records from two ice cores in Tibetan Plateau are compared each other and with other proxy data, such as loess, lake sediments, pollen, changes of sea and lake levels in different parts of China. After an abrupt cooling event of Younger Dryas between 12.2 ka and 10.5 ka BP, {δ 18O} values in the Guliya ice core (35°17′ N, 81°29′ E, {6 710} m a.s.l) in the early Holocene between 10^5 ka BP and 7^2 ka BP were high, indicating the continues warmer and wetter climatic conditions lasted for 3 000 a. Whereas in the mid-Holocene between 7^2 ka BP and 5^0 ka BP, another abrupt cooling occurred, reflected by a sudden decrease of isotopic composition from 7^2 ka BP. Then {δ 18O} values gradually increased from 5^0 ka BP to present, except for a relative lower isotopic stage between 3^5 ka and 2^5 ka. Differentially, in Dunde ice core (38°06′N, 96°24′E, 5 325 m a.s.l.), frequent variations of higher and lower {δ 18O} values have observed during the Holocene. The megathermal maximum started from 8^7 ka BP, characterized by a sharp increase of δ+{18}O values, continued until 3^0 ka BP, and followed by a gradually decreased trend of isotopic composition. However, many short-term colder stages appeared in the more than {5 000} a long Megathermal period of the Holocene, especially there was an unstable-temperature stage between 6^0 ka BP and 5^0 ka BP. Climatic changes indicated by isotopic records in the two cores are inconsistent, probably as a result of differences of altitudes and atmospheric circulations when ice was deposited. It is inferred that air masses with more precipitation at Guliya came from the continental sources due to its interior position and higher altitude in Tibetan Plateau but precipitation at Dunde was disturbed by maritime air masses of the summer monsoon because its site is located in the edge of the plateau and at a lower elevation. There are different climatic indications of {δ 18O} values between continental and maritime-origin vapor sources, which have been confirmed by some studies dealing with the isotopic distribution of precipitation in Tibetan plateau. = Paleoclimatic data from other mediums in different parts of China are used to compare with the climatic records from above two ice cores. In the most loess profiles studied, higher magnetic rates were measured between 10^0 ka BP and 5^0 ka BP, when a warmer and wetter period appeared, and then became progressive cooling in late {5 000} a, with overall decreased magnet rates, although there were some higher-rate stages during the period, corresponding to the higher sea levels in eastern China. However, higher levels of lakes in western China occurred longer, from 10^0 ka BP to 4^0～3^0 ka BP. Climatic warming in the Holocene indicated by pollen charts from lacustrine deposits seems starting earlier in western China than that in eastern China. Proxy data from most mediums displays obvious climatic fluctuations in the most recent 500 a, named as the Little Ice Age.= In summary, climatic records in the Holocene recovered from the Guliya and Dunde ice cores are inconsistent because of their different locations and elevations, which may be controlled by different atmospheric situations when ice formed. The climatic changes indicated by the Guliya ice core in the interior of the Tibetan Plateau correspond well to the climatic records from other polar and tropical ice core, such as those from Greenland and Huascaran, as well as those from deep-sea sediments, which probably reflects a global climatic trend during the Holocene. However, the climatic information in the Dunde ice core is more complex and associated with the proxy climatic data from other mediums, such as loess, lacustrine sediments, changes of sea and lake levels in eastern and middle parts of China, which was more influenced by the prevailing monsoon during the Megathermal in the Holocene. Referring to the most proxy data, it seems that the climate varied earlier and more sensitive in high