P2C2: Geophysical Reconnaissance to Expand Ice Core Hydroclimate Reconstructions in the Northeast Pacific

总的来说，该奖项旨在探索过去一千年可能因厄尔尼诺-南方涛动（ENSO）平均状态变化而发生的水文气候变化。通过推动美国东北太平洋地区过去千年冰芯积累记录时空网络的发展，本研究将促进对ENSO耦合系统的区域水文响应的更好理解。研究人员提出了一个假设，即从中世纪气候异常（MCA）期间持续的类似拉尼娜的状态到小冰期（LIA）期间持续的类似厄尔尼诺的状态发生了变化。研究小组将通过重建和评估东北太平洋在MCA-LIA过渡期间的空间降水异常模式来验证这一假设。他们的假设是建立在现代观测的基础上的，这些观测表明，在拉尼娜（厄尔尼诺）现象期间，该地区的沿海-内陆降水梯度增强（减弱）。研究人员预测，东北太平洋降水异常模式将在MCA-LIA过渡期间减弱。该项目将支持一位早期职业科学家，为本科生和研究生提供支持，并通过PolarTREC项目（美国国家科学基金会资助的项目，旨在将K-12教师与极地研究人员联系起来，目标是将极地科学研究纳入K-12课程）向K-12教师和学生提供支持。就推进这一科学领域的知识水平而言，拟议科学的潜在投资回报很高，对早期职业科学家的支持和提案的推广方面对NSF的使命和授权非常重要。在过去的十年里，研究人员一直在美国东北太平洋开发一个冰芯阵列，目标是降水偶极子的两个节点（即圣埃利亚斯山脉和阿拉斯加中部）。最近一次获得冰芯是在2013年，从德纳里国家公园的亨特山（Mt. Hunter）回收了两个210米的地表到基岩的冰芯。为了确定过去一千年来亨特山地区的降水变化，研究人员将依靠一套支持性的地球物理数据，在三维有限元数值模型中约束冰川的几何形状、速度、边界条件和流变特性。综合观测和模型数据集将使该小组能够消除冰流（导致冰层变薄）和积雪率的空间变异性的影响，从而从两个冰芯估计积雪的时间变异性。与亨特山相比，人们对圣埃利亚斯山脉沿海冰芯地点（罗根山上的PR Col、NW Col、King Col和Eclipse冰原）的地球物理特征知之甚少，这些地点是在2002年钻探的，当时地球物理技术和数值模拟能力还没有取得最新进展。这种信息的缺乏将在圣埃利亚斯和亨特山积累记录的任何比较中引入错误，从而对MCA-LIA过渡假设进行评估。因此，研究小组特别提出，通过在圣埃利亚斯山脉现有的冰芯地点收集新的地球物理数据，改进基于冰芯的积累记录，从而重建东北太平洋过去一千年的水文气候。科学目标是：1)绘制Eclipse冰原、King Col和Mt Logan山顶高原地点的基岩地形图；2)确定所有站点的地表速度；3)绘制近地表空间累积速率格局；4)追踪各测点的内部等时线；5)估算冰变形对冰层减薄的影响；6)在所有站点生成更新的，到2016年的和校正的累积时间序列；7)比较Hunter山和St. Elias站点的修正累积记录，以评估过去一千年的空间降水模式。研究策略需要使用最先进的探地雷达（GPR）、地球化学、卫星遥感、数值模拟和数据合成技术。

Generally, this award aims to explore hydroclimate changes over the past Millennium that possibly occurred in response to changes in the mean state of the El Nino-Southern Oscillation (ENSO). By advancing the development of a spatial-temporal network of ice core accumulation records covering the past millennium in the NE Pacific region of the United States, this research will foster a greater understanding of regional hydrologic response to the coupled ENSO system.The researchers propose to investigate the hypothesis that a change occurred from a persistent La Nina-like state during the Medieval Climate Anomaly (MCA) to a persistent El Nino-like state during the Little Ice Age (LIA). The research team will test this hypothesis by reconstructing and evaluating the spatial precipitation anomaly pattern in the Northeast Pacific across the MCA-LIA transition. Their hypothesis is founded on modern observations that show an enhanced (weaker) coastal-inland precipitation gradient in the region during La Nina (El Nino) conditions. The researchers predict that the NE Pacific precipitation anomaly pattern will weaken across the MCA-LIA transition.The project will support an early career scientist, provide support for undergraduate and graduate students, and enable outreach to K-12 teachers and students through the PolarTREC program, an NSF funded program which seeks to link K-12 teachers with Polar researchers with a goal of integrating polar science research into K-12 curriculum. The potential return on investment of the proposed science is high in terms of advancing the state of knowledge in this area of science and the support of early career scientists and outreach aspects of the proposal are important to the NSF Mission and mandate.For the past decade, the researchers have been developing an ice core array in the NE Pacific of the United States that targets the two nodes of this precipitation dipole (i.e., St. Elias Range and Central Alaska). The most recent ice core acquisition was in 2013 with the recovery of two surface-to-bedrock 210-meter ice cores from Mt. Hunter in Denali National Park. To determine precipitation variability at the Mt. Hunter site over the past millennium, the researchers will rely on a suite of supporting geophysical data to constrain glacier geometry, velocity, boundary conditions, and rheological properties in a 3-dimensional finite element numerical model. The combined observational and model datasets will allow the team to remove influences of ice flow (which causes layer thinning) and spatial variability in snow accumulation rate to estimate temporal accumulation variability from the two ice cores.In contrast to Mt. Hunter, little is known about the geophysical characteristics of the coastal St. Elias Range ice core sites (PR Col, NW Col, King Col on Mt Logan and the Eclipse Icefield), which were drilled in 2002 prior to recent advances in geophysical techniques and numerical modeling capability. This lack of information would introduce error in any comparison of the St. Elias and Mt. Hunter accumulation records, and thus evaluation of the MCA-LIA transition hypothesis.Consequently, the research team specifically proposes to improve ice core-based accumulation records, and therefore hydroclimate reconstructions for the past millennium, in the NE Pacific through the collection of new geophysical data at existing ice core sites in the St. Elias Range. The science objectives are to: 1) develop bedrock topography maps of the Eclipse Icefield, King Col, and Mt. Logan summit plateau sites; 2) determine surface velocities at all sites; 3) map near-surface spatial accumulation rate patterns; 4) trace internal isochrones at all sites; 5) estimate ice deformation effects on layer thinning; 6) produce updated, to 2016, and corrected accumulation time series at all sites; and 7) compare corrected accumulation records from the Mt. Hunter and St. Elias sites to evaluate spatial precipitation patterns over the past millennium. The research strategy necessitates the use of state-of-the-art ground penetrating radar (GPR), geochemical, satellite remote sensing, numerical modeling, and data synthesis techniques.