(ESH) The Development of the Asian Monsoon: Seasonal Isotopic Variation in the Paleorivers of Nepal, 12 Ma to 1 Ma

(ESH) 亚洲季风的发展：尼泊尔古河流的季节性同位素变化，12 Ma 至 1 Ma

• 批准号: 9510033
• 负责人: David Dettman
• 金额: $ 6.42万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-08-01 至 1997-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9510033&HistoricalAwards=false
• 关键词: ESH; Development; Asian; Monsoon; Seasonal

9510033 Dettman The Asian Monsoon is one of the largest and most important weather systems on Earth. The development of a strong monsoon climate has been identified as a possible cause of the expansion of C4 grasslands and an oxygen isotope shift in soil carbonates in Pakistan and Nepal. This study will examine the development of the modern monsoon, one dominated by the high Tibetan Plateau which today virtually precludes any dry-season precipitation. The isotopic composition of aragonitic molluscs will be used to reconstruct the seasonal isotopic variation of rivers in the foothills of the Himalayas between 12 and 1 Ma (million years before present). By combining the 18O of micro-sampled weekly or monthly shell growth increments with temperature estimates based on fossil floral assemblages, the seasonal change in the 18O of river water can be calculated. The goal of these measurements is to examine the isotopic composition of river waters on a seasonal basis in order to estimate the aridity of the dry season and the seasonal variability of rainfall. Strong seasonal aridity is indicated by positive 18O values of surface water in the dry season. The seasonal amount of precipitation can be roughly estimated because the isotopic composition of rainfall is a function of the amount of rainfall at low latitudes. Shell carbonates 13C of carbon in the rivers. This allows changes in the 18O record to be directly related to changes in the plant biomass of the region (C3 versus C4). Nepal will be the primary focus of this study because of the useful stratigraphic distribution of well preserved molluscs, but some shell beds in Pakistan will also be studied to allow comparison of different regions under the influence of the Asian Monsoon.

9510033 Dettman亚洲季风是地球上最大，最重要的天气系统之一。 强烈的季风气候的发展已被确定为巴基斯坦和尼泊尔土壤碳酸盐中C4草原膨胀和氧同位素转移的可能原因。 这项研究将研究现代季风的发展，现代季风的发展是由高藏高原主导的，如今几乎无法排除任何干季降水。 后期软体动物的同位素组成将用于重建喜马拉雅山山麓河流的季节性同位素变化，在12到1 MA（在目前的百万年前）之间。通过将18O的微采样的每周或每月壳生长增量与化石花卉组合的温度估计相结合，可以计算出18O河水的季节性变化。 这些测量的目的是在季节性检查河水的同位素组成，以估计干旱季节的干旱和降雨的季节变化。 在干旱季节，地表水值的正值表明强烈的季节性干旱。 可以大致估算季节性降水量，因为降雨的同位素组成是低纬度降雨量的函数。 壳在河流中碳酸盐13C。 这允许18O记录的变化与该地区植物生物量的变化直接相关（C3对C4）。 尼泊尔将成为这项研究的主要重点，因为保存完好的软体动物的有用地层分布，但是还将研究巴基斯坦的一些贝壳床，以允许在亚洲季风的影响下比较不同地区。