Primary study on the environmental significances of grain-size changes of the Lake Bosten sediments

Abstract

æ¹–æ³Šæ²‰ç§¯ç‰©çš„ç²’åº¦åˆ†æž æ˜¯ä¸€ç§ ç ”ç©¶å ¤çŽ¯å¢ƒå ˜åŒ–å¸¸ç”¨çš„æ‰‹æ®µ,ä½†æ˜¯å…¶çŽ¯å¢ƒæ„ ä¹‰å…·æœ‰å¤šè§£æ€§,尤其是沙(è ’)æ¼ å¹²æ—±åŒºçš„æ¹–æ³Šæ²‰ç§¯ç‰©ç²’åº¦å ˜åŒ–,代表的是沙尘天气的多寡 å¼ºå¼±è¿˜æ˜¯å…¶å®ƒçŽ¯å¢ƒå› ç´ çš„å ˜åŒ–å€¼å¾—ç»†è‡´ç ”ç©¶.在对我国最大的内陆淡水湖--æ–°ç–†å šæ–¯è…¾æ¹–çš„æ²‰ç§¯ç‰©çŸå²©èŠ¯è¿›è¡Œäº†~(210)Pbex,~(137)Cs定年的 基础上.对近50å¤šå¹´æ²‰ç§¯ç‰©çš„ç²’åº¦è¿›è¡Œåˆ†æž ,ç»“æžœè¡¨æ˜Žå¹³å ‡ç²’å¾„ä¸Žç²—é¢—ç²’å «é‡ ä¸ŽåŒºåŸŸæœ€å¤§æ²³æµ --å¼€éƒ½æ²³å¤§å±±å £ç«™çš„æœ€å¤§ä¸€å¤©æ´ªé‡ ã€ æ´ªå³°æµ é‡ .å¤©å±±å·´éŸ³å¸ƒé² å…‹ç«™ å¹´é™ æ°´é‡ ã€ æ¹–æ³Šæ°´ä½ å ˜åŒ–ä»¥å Šæ¹–æ³Šé™„è¿‘ç„‰è€†ç«™3-6æœˆé£ŽåŠ›å¼ºåº¦å ˜åŒ–è®°å½•ç‰çŽ¯å¢ƒå› ç´ å¯¹æ¯”å ‘çŽ°,湖泊ä¸éƒ¨æ²‰ç§¯ç‰©ä¸ç²—é¢—ç²’å «é‡ å ˜åŒ–ä¸»è¦ å æ˜ çš„æ˜¯å…¥æ¹–æ²³æµ å¾„æµ é‡ ã€ åŒº åŸŸæ´ªæ°´å¼ºåº¦å Šé¢‘çŽ‡ã€ å±±åœ°é™ æ°´,è€Œå¹¶ä¸ å æ˜ å¤§é£Žå¤©æ°”æˆ–è€…æ¹–æ³Šæ°´ä½ çš„å ˜åŒ–.å¯¹å…¶è¿‘å ƒå¹´æ²‰ç§¯å²©èŠ¯çš„å¤šæŒ‡æ ‡åˆ†æž ç»“æžœè¡¨æ˜Ž,å ³ä½¿åœ¨æ•°ç™¾å¹´æ—¶é—´å°ºåº¦ä¸Š,å šæ–¯è…¾æ¹–æ²‰ç§¯ç‰© ç²’åº¦çš„çŽ¯å¢ƒæ„ ä¹‰ä¾ ç„¶ä¸Žå 年时间尺度上一致. Grain size analysis is a conventional method to explore paleo-environmental changes, but its environment significance has various explanations. Especially for the lake sediments preserved in dry-land area close to Gobi and desert, it is still unclear if the grain size represents the intensity and frequency of the dust weather or the other environmental indicators. Based on the ~(137)Cs and ~(210)Pbex activities from a short-length Glew core drilling from the center of Lake Bosten, the largest inland freshwater lake in China, grain size analysis of the past 50 years of lake sediments suggests that the average grain size and coarse grains content coincide with the maximum one-day runoff and the flood peak runoff at Dashakou station of Kaidu River, and with the annual precipitation of Bayinbuluke Station in the Tianshan Mts. However, the peaks of grain size curves were not consistent with lake level variations or wind speed changes （from March to June） of the Yanqi Station near to Lake Bosten. Therefore, the coarse grains content and average grain size can generally represent intensity and frequency of flood events of the Kaidu River and strong precipitation in the surrounding Tianshan mountainous area, but do not indicate lake level variations nor wind speed changes. A millennial multi-proxy record of Lake Bosten also suggests that the environmental significance from grain size at centennial or multi-centennial timescales is the same as that at annual to decadal timescales.