(ESH) Paleoenvironmental Change in the Atacama Desert During the Late Quaternary: Evidence from Middens and Paleosprings

智利北部/秘鲁南部1500公里样带沿线的关键地点的啮齿类昆虫化石和古河流沉积物将用于重建阿塔卡马沙漠晚第四纪的植被和气候历史。在阿塔卡马沙漠研究这些沉积物有几个优点：1)与湖泊记录不同，泥炭和春季沉积物含有丰富的维管植物，在14C测年中不受“硬水”影响；2)降雨季节性可以从与夏季或冬季降水有关的植物种类的中间出现推断出来；3)大多数阿塔卡马植物的海拔下限反映了当地降水(而不是生长季的温度)，而泉水的水位反映了安第斯山脉高地的区域积雪；4)中亚和春季沉积物普遍存在，并保存了绝对沙漠上部边缘的植被和水位的区域历史。还将分析土壤碳酸盐中的碳同位素，并将绘制绝对沙漠部分地区可能经历了持续降雨和植被扩张时期的残留水系网络。将对受不同天气气候影响的三个关键地区进行采样，预计将出现不同步的气候历史。秘鲁阿雷基帕(16.5 S)附近的蚊虫和春季沉积物将使支持者能够追踪喀喀湖以西仅200公里处夏季降水的变化。智利科皮亚波(S 27)附近的地点，圣地亚哥以北600公里，应该会隔离出温带冬季降水强度的变化。智利加莱纳附近的中心地点横跨摩羯座北回归线(23·5 S)，将揭示热带和温带雨带之间的相互作用。拟议的研究将有助于完善目前对南美洲亚热带地区第四纪晚期气候变化的性质和时间及其水文和生态影响的理解。

Fossil rodent middens and paleospring deposits at key sites along a 1500-km transect in northem Chile/southern Peru will be used to reconstruct late Quaternary vegetation and climate histories in the Atacama Desert. There are several advantages to studying these deposits in the Atacama Desert: 1) unlike lake records, middens and spring deposits contain abundant vascular plants that suffer no "hard water" effects in 14 C dating; 2) rainfall seasonality can be inferred from midden occurrences of plant taxa tethered to either summer or winter precipitation; 3) the lower elevational limits of most Atacama plants reflect local precipitation (and not growing-season temperature), whereas water levels in springs reflect regional snowpack in the high Andes; 4) both middens and spring deposits are ubiquitous and preserve a regional history of vegetation and water levels along the upper margins of the Absolute Desert. Carbon isotopes in soil carbonates also will be analyzed and relict drainage networks in parts of the Absolute Desert that might have experienced periods of sustained rainfall and vegetation expansion will be mapped.Three key areas affected by different synoptic climatologies will be sampled, and asynchronous climate histories are expected. Middens and spring deposits near Arequipa, Peru (16.5 S) will allow the proponents to track changes in summer precipitation just 200 km west of Lake Titicaca. Sites near Copiapo, Chile (27 S), 600 km north of Santiago, should isolate variations in the strength of extratropical winter precipitation. The central sites near Calaina, Chile, straddle the Tropic of Capricorn (23.5 S) and will reveal the interplay between tropical and extratropical rainfall belts. The proposed research will help refine current understanding of the nature and timing of late Quaternary climate change, and its hydrological and ecological effects, in subtropical South America.