發(fā)布時(shí)間：2018-04-24 23:38

  本文選題：班公錯(cuò) + 介形蟲(chóng)組合　； 參考：《蘭州大學(xué)》2016年碩士論文

【摘要】：亞洲季風(fēng)是全球大氣環(huán)流的重要組成部分,深入研究季風(fēng)區(qū)氣候變化歷史及其驅(qū)動(dòng)機(jī)制具有重要意義。本文選擇季風(fēng)邊緣區(qū)西藏西北部的高山湖泊班公錯(cuò)作為研究對(duì)象。利用巖芯沉積物中的全有機(jī)質(zhì)和植物殘?bào)w進(jìn)行AMS14C測(cè)年,評(píng)估碳庫(kù)效應(yīng)后建立了BGC-2011孔的年代序列。分析了沉積物巖芯中介形蟲(chóng)種屬、碳酸鹽含量、粒度和細(xì)粒碳酸鹽同位素等指標(biāo)。通過(guò)調(diào)查湖泊現(xiàn)代沉積物、水樣和植被,明確了各個(gè)代用指標(biāo)的指示意義。結(jié)果顯示粒度與介形蟲(chóng)種屬可以有效指示水位變化。碳酸鹽氧同位素(δ18Ocarb)主要反映了湖水同位素(δ18Ow)變化,δ18Ow主要受大氣降水同位素(δ18Op)及湖泊水文環(huán)境影響,進(jìn)而可以指示印度夏季風(fēng)強(qiáng)度。利用各代用指標(biāo)變化重建了班公錯(cuò)湖區(qū)過(guò)去14.3 cal ka BP以來(lái)的環(huán)境演化歷史。BGC-2011孔代用指標(biāo)揭示的末次冰消期以來(lái)該地區(qū)氣候環(huán)境變化大致可以分為三個(gè)階段:1)晚冰消期14.3~11.5 cal ka BP:介形蟲(chóng)組合、碳酸鹽含量、粗顆粒組分及δ18Ocarb指示湖泊水位較低,湖泊水體鹽度較高且不穩(wěn)定,沉積物受近岸碎屑影響;2)全新世11.5~3.4 cal ka BP:早全新世(11.5~7.8 cal ka BP)各指標(biāo)表明湖面擴(kuò)張,湖水變暖淡化,湖泊開(kāi)放,鉆孔位置處于靜水深水環(huán)境;其中7.8~6.4 cal ka BP溫度較高使湖泊蒸發(fā)增強(qiáng),湖泊生產(chǎn)力較高;中全新世(6.4~3.4 cal ka BP)入湖水量減少,湖水變冷,氣候轉(zhuǎn)型。3)晚全新世3.4 cal ka BP至今:湖泊水位下降,脫離深水靜水環(huán)境,氣候環(huán)境向干旱化方向發(fā)展。約0.8 cal ka BP淡水種介形蟲(chóng)消失,δ18Ocarb劇烈偏正,表明干旱化加劇,湖泊處于封閉狀態(tài)。與青藏高原湖泊沉積δ18Ocarb及季風(fēng)區(qū)、非季風(fēng)區(qū)記錄對(duì)比,發(fā)現(xiàn)14.3 cal ka BP以來(lái)班公錯(cuò)湖泊沉積記錄的氣候變化同印度季風(fēng)演變具有較好的一致性,區(qū)域氣候環(huán)境變化主要受太陽(yáng)輻射量變化控制。晚冰消期氣候波動(dòng)較大,記錄了B/A暖期和YD事件;早全新世印度季風(fēng)增強(qiáng),氣候溫暖濕潤(rùn),出現(xiàn)全新世適宜期;中全新世太陽(yáng)輻射量降低導(dǎo)致印度季風(fēng)衰退,氣候向干冷方向轉(zhuǎn)型;晚全新世印度季風(fēng)進(jìn)一步減弱,區(qū)域環(huán)境干旱化顯著。
[Abstract]:The Asian monsoon is an important part of the global atmospheric circulation. It is of great significance to study the history of climate change and its driving mechanism in the monsoon region. In this paper, the alpine lakes of northwestern Tibet are selected as the research object. The AMS14C dating of total organic matter and plant residues in core sediments was used to evaluate the carbon pool effect and the chronological sequence of the BGC-2011 pore was established. The species, carbonate content, granularity and fine carbonate isotope of sediment core were analyzed. By investigating the modern sediments, water samples and vegetation of lakes, the indicative significance of each substitute index is clarified. The results showed that granularity and ostracoda species could effectively indicate water level change. The 未 18 oxygen isotope (未 18 O carbonic) mainly reflects the variation of 未 18 Owns in lake water, and 未 18Ow is mainly influenced by the atmospheric precipitation isotope (未 18 Op.) and the hydrological environment of the lake, thus indicating the intensity of Indian summer monsoon. The environmental evolution history since 14.3 cal ka BP in the past 14.3 cal ka BP in Bangongcao Lake region has been reconstructed by using the variation of various proxy indexes. The climatic and environmental changes in the region since the last ice elimination period revealed by the BGC-2011 hole replacement index can be roughly divided into three stages: 1) late ice. 14.3 cal cal BP: ostracoda combination. The carbonate content, coarse particle composition and 未 18Ocarb indicate that the water level of the lake is low, the salinity of lake water is high and unstable, and the sediment is affected by nearshore clastic. The sediment is affected by 11. 5 ~ 3. 4 cal ka BPin Holocene and 11. 5 ~ 7. 8 cal cal BP in early Holocene. The lake water becomes warm and desalination, the lake is open and the borehole is located in the deep water environment, the evaporation of the lake increases with the temperature of 7.86.4 cal ka BP, the productivity of the lake is higher, and the water inflow of the lake decreases and the water of the lake becomes colder in the middle Holocene. Climate transition. 3) from late Holocene 3.4 cal ka BP up to now: the lake water level drops away from the deep-water still water environment and the climate environment develops towards the direction of drought. The ostracod of freshwater species of about 0.8 cal ka BP disappeared and 未 18Ocarb was skewed sharply, indicating that the drought was aggravated and the lake was in a closed state. Compared with 未 18Ocarb in lake sediments and monsoon and non-monsoon regions in the Qinghai-Xizang Plateau, it is found that the climate changes recorded in the lake sediments of Bangongco since 14.3 cal ka BP are in good agreement with the Indian monsoon evolution. The change of regional climate and environment is mainly controlled by the amount of solar radiation. During the late ice extinction period, the climate fluctuated greatly, recording the B / A warm period and the YD event; the early Holocene Indian monsoon strengthened, the climate was warm and humid, and the suitable period of the Holocene appeared. The decrease of solar radiation in the Middle Holocene resulted in the Indian monsoon recession. The late Holocene Indian monsoon weakened further and the regional environment became dry.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：P532

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