Collaborative Research: RUI: Tropical Holocene climatic insights from Andean paleoglacier dynamics

该基金支持对秘鲁全新世（~12 ka至今）山区冰川作用的连续、百年至千年尺度的记录进行研究，以检验有关热带地区气候突变原因的假设。冰川粉通量的放射性碳和210Pb定年提供了全新世冰川前进/后退的精确年龄和气候突变的记录，使用了来自秘鲁安第斯山脉中部陡峭的东西湿度梯度的多个湖泊的前冰期湖泊沉积物岩心。冰川粉的通量是根据多种代用品确定的，其分辨率足以与该地区现有的古气候变率的稳定同位素记录进行比较。先前在热带安第斯山脉的工作表明，冰川粉方法可以提供与辐射定年冰碛记录一致且远比其更连续的冰川作用记录。这种方法有可能解决几个冰川地质上的不确定性，例如全新世早期冰川推进的时间，以及新冰川期间冰缘波动的可能的时间海侵性质。冰川-湖泊方法结合详细的冰碛测绘和宇宙成因放射性核素定年的定向应用，从取心位置选择位于山谷上游的全新世冰碛。冰期面粉记录与年代冰碛的策略性配对提供了冰缘变化的时间和幅度。不同降水条件下多个流域的冰川质量平衡-冰流逆模拟为全球尺度环流和古气候模式的动态降尺度提供了验证。知识价值和更广泛的影响：将热带冰川质量的变化与气候动力学联系起来，是全球气候模拟工作的一个重点，以便在准确模拟不同温室情景下过去的变化的基础上预测未来的变化。温度和降水变化对热带冰川质量和能量平衡的长期影响仍然知之甚少，这主要是因为缺乏来自热带安第斯山脉湿润和干旱地区的详细和连续的冰川记录。这项工作大大提高了我们对高山冰川变化、水资源以及地球热带“热机”中质量和能量通量之间联系的理解。这些记录有助于更好地了解全新世高海拔（5000 - 6000 masl）热带大气变化的时间、幅度和空间范围，从而评估低纬度水文循环在全球气候突变中的作用。反过来，将能够验证以下假设：(1)全新世热带安第斯山脉冰川边缘的波动是由南美夏季风强度的变化驱动的(2)全新世冰川变化的广泛区域模式被每~1000 ~ 1500年的快速冰推进期所打断(3)南部热带地区全新世冰川的突变（百年至千年尺度）几乎与北半球的冰川变化同步(即小冰期)

This grant supports research generating continuous, centennial to millennial-scale records of mountain glaciation in Peru spanning the Holocene (~12 ka to present) that tests hypotheses concerning the causes of abrupt climate change in the tropics. Radiocarbon and 210Pb dating of glacial flour flux provides precise ages of Holocene ice advances/retreats and records of abrupt climatic transitions, using proglacial lake sediment cores from multiple lakes along the steep East-West moisture gradient across the central Peruvian Andes. The flux of glacial flour is determined based on multiple proxies at a resolution sufficient to enable comparison with existing stable isotope records of paleoclimate variability from the region. Previous work in the tropical Andes demonstrates that the glacial-flour approach can provide a record of glaciation that is both consistent with and far more continuous than radiometrically-dated moraine records. This approach has the potential to resolve several glacial geologic uncertainties, such as the timing of early Holocene glacial advances, and the possible time-transgressive nature of ice margin fluctuations during the neoglacial. The glacial-lacustrine approach is coupled with detailed moraine mapping and the targeted application of cosmogenic radionuclide dating to select Holocene moraines located up-valley from coring localities. The strategic pairing of glacial flour records with dated moraines provides both the timing and magnitude of ice margin changes. Inverse glacier mass balance-ice flow simulations from multiple watersheds in different precipitation regimes provide validation for the dynamical down-scaling of global-scale circulation and paleoclimate models.Intellectual Merits and Broader Impacts: Relating the changes in tropical glacier mass to climate dynamics is a priority for global climate modeling efforts to predict future changes based on accurately simulating past changes under different greenhouse scenarios. The long-term perspective of temperature and precipitation changes on tropical glacier mass and energy balance is still poorly understood, primarily because of a lack of detailed and continuous glacial records from both the humid and more arid parts of the tropical Andes. This work substantially improves our understanding of the link between alpine glacial variability, water resources and mass and energy fluxes in the tropical "heat engine" of the planet.These records are needed to better understand the timing, magnitude, and spatial extent of high elevation (5000 - 6000 masl) tropical atmospheric change during the Holocene to evaluate the role of the low latitude hydrologic cycle in abrupt global climatic shifts. This, in turn, will enable testing of the following hypotheses:(1) Glacier margin fluctuations in the tropical Andes during the Holocene were driven by changes in the strength of the South American Summer Monsoon(2) A broad regional pattern of Holocene glacial variability was punctuated by periods of rapid ice advances every ~1000 to 1500 years(3) Abrupt (centennial to millennial-scale) Holocene glacier variations in the southern tropics were nearly synchronous with those in the Northern Hemisphere (i.e. The Little Ice Age)