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首页> 外文学位 >Geochemical investigations of Quaternary paleoclimate and environmental change from Lake Titicaca, South America and Prydz Bay, Antarctica.
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Geochemical investigations of Quaternary paleoclimate and environmental change from Lake Titicaca, South America and Prydz Bay, Antarctica.

机译：南美洲的喀喀湖和南极普里兹湾的第四纪古气候和环境变化的地球化学研究。

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This dissertation is comprised of multi-proxy investigations of Quaternary paleoclimatic and environmental change from two regions of importance to the global climate system: the Central Andes of South America and East Antarctica.; A study of the stable isotopic, elemental, and sedimentary characteristics of a unique set of mid-Holocene age laminated sediments from Lake Titicaca provides a high-resolution record of climate variability for the northern Altiplano region of South America. The results of this study indicate that the mid-Holocene multi-millennial drought featured at least three multidecadal-century scale arid episodes in which lake level dropped by up to 30 meters. Each of these episodes would have required instantaneous reductions of 10–50% in precipitation or 2–8°C increases in temperature. A study of the distribution of three different classes of lipid molecular fossils gives clues to the ecological history of Lake Titicaca over the past 25,000 years. Sharp changes in lake ecology occurred during the mid-Holocene in response to the long-term drought. Mid-Holocene Lake Titicaca is distinguished from other periods by being dominated by a few opportunistic algal species, probably one or two dinoflagellate and chrysophyte species that are presently rare or absent in the lake. The presence of long-chain alkenones in mid-Holocene sediments gives a relative indicator of lake temperature and the possibility of an indicator of absolute lake temperature if the source organism can be identified.; Changes in the size of the Lambert Glacier-Amery Ice Shelf system serve as a proxy for the larger East Antarctic Ice Sheet. Stable isotopic measurements of Neogloboquadrina pachyderma (s.) planktonic foraminfers coupled with sedimentary data from Ocean Drilling Program Hole 1167A drilled in the Prydz Channel Trough Mouth Fan suggest long-term cooling and ice sheet growth since the early Pleistocene. A “warm” interglacial indicated by lowered δ18O values and sedimentary evidence occurred between 0.9–1.38 Ma. Stable isotopic results indicate only two glacial-interglacial cycles stratigraphically between the Brunhes-Matuyama paleomagnetic reversal (780 Ka) and a much younger date at the top of the core (36.9 Ka), raising the possibility that there have been few extreme advances of the ice sheet across Prydz Bay since mid-Pleistocene time.
机译：本论文包括对从两个重要的地区到全球气候系统的第四纪古气候和环境变化的多代理研究：南美中部安第斯山脉和南极东部。对来自喀喀湖的一套独特的中全新世年龄层状沉积物的稳定同位素，元素和沉积特征的研究，为南美北部高原地区的气候变化提供了高分辨率记录。这项研究的结果表明，全新世中期的千年干旱至少发生了三个十年以上的干旱，其中湖泊水位下降了30米。这些事件中的每一个都需要瞬时减少10–50％的降水或2–8°C的温度升高。对三种不同类别的脂质分子化石分布的研究为过去的25,000年的喀喀湖生态历史提供了线索。在全新世中期，由于长期干旱，湖泊生态发生了急剧变化。喀喀湖中全新世湖与其他时期的区别在于，它被一些机会性藻类所控制，这些藻类可能是目前湖中稀有或不存在的一种或两种藻鞭毛和金绿藻。全新世中期沉积物中长链烯酮的存在提供了湖泊温度的相对指标，并且如果能够确定源生物，则有可能提供湖泊绝对温度的指标。 Lambert Glacier-Amery冰架系统尺寸的变化可替代较大的南极东部冰原。浮游有孔虫的斜体同位素测量稳定，再加上在Prydz海槽低谷扇中钻进的海洋钻探计划洞1167A的沉积数据，表明自早更新世以来长期冷却和冰盖生长。 δ 18 O值降低表示“暖”间冰期，而沉积证据则出现在0.9-1.38 Ma之间。稳定的同位素结果表明，在Brunhes-Matuyama古地磁逆转（780 Ka）到岩心顶部年轻得多的日期（36.9 Ka）地层之间只有两个冰-冰间旋回，这增加了极少数极端进展的可能性。自更新世中期以来，整个普莱兹湾的冰盖都已形成。

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