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Biomarker Distributions And Compound Specific Carbon Isotopic Compositions From Loess Sequence In Arid Central Asia And Thei R Responses To Paleoclimate Since MIS3

Posted on:2014-01-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q L YangFull Text:PDF
GTID:1220330398469621Subject:Environmental Science
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Arid Central Asia is one of the most sensitive area response to climate change because it is a converge area of three main climatic systems (westerlies, East Asia monsoon and polar airmass). Therefor, it should be helpful for understanding dynamic and process of global change via researching paleoclimate change in arid Central Asia. Whereas, studies based on paleoclimate records is still incomplete, most of which are in Holocene and few of which could reach MIS3although in a low resolution. The detail of climate change in arid Central Aisa is still unknown since MIS3.This dissertation focuses on three loess-paleosoil sequences (VA, TR and RM) in Kazakhstan, which locate in the core area of arid Central Asia. Based on analysis of biomarker, compound specific carbon isotopic compositions, multi-proxies (including pollen, particle size, TOC, carbonate, magnetic susceptibility, strata) and reliable AMS14C dating results, a reconstruction of climate change history is built since MIS3. Meanwhile, features of biomarker and compound specific carbon isotopic compositions from loess-paleosoil sequences and their responses to climate change are discussed and verified. The main conclusions are as follows:(1) Climate restruction of VA section (western):32-20ka BP, humid.20-11ka BP, humidity decreased.11-7ka BP, arid.7-4ka BP, humidity increased. After4ka BP, climate tended to arid.(2) Climate restruction of TR and RM (easten):50-43ka BP, arid.43-37ka BP, mild humid.37-34ka BP, arid again.34-30ka BP, humidity increased.30-25ka BP, humid.25-11ka BP, arid.11-6ka BP, mild wet. After6ka BP, climate tended to arid.(3) Comparing lots of records from arid Central Asia suggests the climatic condition was mainly controlled by westerlies system, which brought most moisture to research area since MIS3. In that case, humidity increased in early and middle Holocene followed stronger westerlies resulting from energy enrich (possible NAO positive phase).(4) Local evaporation capability could affect effective humidity dramatically in arid Central Asia. During the cold Last Glacial Maximum (LGM), humid condition appeared in research area is caused of evaporation capability decreasing and precipitation increasing.(5) Distribution characteristics of n-alkane, as one kind of common biomarker, could indicate sources of organic matters very well. The compound specific carbon isotopic compositions have a close relation with humidity, which is more negative when humidity increase. On contrast, it become more positive when humidity decrease. Besides, compound specific carbon isotopic compositions is more reliable as climatic indicator than δ13Corganic, which could biased in multi-source organic matter’s mixture.
Keywords/Search Tags:Biomarker, Specific carbon isotopic composition, Arid Central Asia, Loess-paleosoil sequence
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