Collaborative Research: GreenTrACS: a Greenland Traverse for Accumulation and Climate Studies

在未来海平面上升的背景下，格陵兰冰盖的稳定性对科学家和整个社会至关重要。格陵兰冰盖将在多大程度上失去质量并导致海平面上升
在未来几十年里，冰川融化的速度取决于冰川边缘的流量和表面物质平衡，即积雪和表面融化之间的平衡。对格陵兰地表物质平衡的估计越来越多地利用气候再分析和高分辨率区域气候模型来确定积雪、地表融化和径流/再冻结。这些模型显示出显着的，依赖于模型，沿着格陵兰冰盖的陡峭边缘的偏差（从观察的差异），最高和最可变的（在空间和时间）积累和表面融化率观察。因此，格陵兰冰盖的边缘迫切需要更新的积累和融化数据，以验证模型和改进质量平衡估计。研究人员建议在格陵兰西部渗滤区进行两个野外季节的穿越，使用地面雷达和浅层积雪芯来记录连续的原位积雪和积雪密度。研究目标包括：（1）确定过去20-40年西格陵兰积雪的时间和空间模式;（2）评估过去20-40年西格陵兰渗透带的表面融化再冻结和冰内融水储存&;以及（3）量化最新气候再分析模式及其区域气候模式的累积和地表融化偏差。该项目将通过对西格陵兰表面物质平衡的质量增加（积雪）和质量损失（表面融化）组成部分进行现场验证观测，推进知识和理解。自2005年以来，格陵兰冰盖的西部边缘一直在加速失去质量，这主要是由于表面质量平衡下降。然而，从区域气候模式得出的地表物质平衡趋势在该区域相差约2.5倍。西格陵兰雪芯积累的记录，需要模型验证，一般在1996-1998年结束之前，最近一段时间的加速质量损失。研究人员将利用探地雷达，通过频繁的雪坑和#8232;积雪芯（25-30米）的化学分析，对过去20-40年格陵兰西部的积雪进行连续记录。他们还建议使用多偏移雷达方法来计算连续的积雪密度#8232;数据，提供一种方法来评估过去的表面融化，再冻结和当前的融水储存在冰川含水层中。融水再冻结显示最大的变化，在区域气候#8232;模式之间的表面质量平衡组件，因此验证观测是迫切需要的。穿越路线将穿过渗透区，几乎平行于最陡的堆积和表面融化梯度，这将增加用于模型验证的数据集的价值。这次穿越将与以前的穿越路线重叠，并重新占用以前取样的地点，以更新18-20年的雪芯积累记录。此外，该项目将从低海拔数据匮乏地区的新地点收集岩芯，这些地区的堆积和表面融化都在增加，最需要区域气候模型验证。几个气候再分析模型的表面质量平衡验证将导致对当前和未来格陵兰冰盖质量平衡趋势的更准确评估，这对于准确预测未来海平面上升至关重要。该项目将整合研究与学生#8232;学习在多个层次，重点是学生的参与，从代表性不足的群体。该项目将资助四名研究生，并将通过达特茅斯女性科学项目和本科生地球科学联盟多样性等成功项目招募的众多本科生研究人员纳入其中。K-12学生将通过调查为基础的，网络托管的气候课程，结合缅因州气候再分析器和环境变化模型的大学，并通过在博伊西山区侧重于雪科学的实地项目参与这一项目。除了通过各自的公共事务办公室进行频繁的公开演讲和媒体采访之外，PI还将通过既定且成功的项目继续积极开展公众宣传活动，例如每月一次的上谷科学酒吧和一年两次的爱达荷州探索中心雪日活动。

The stability of the Greenland Ice Sheet is of critical interest to scientists and society
at large in the context of future sea-level rise. The extent to which the Greenland Ice Sheet will lose mass and contribute to rising sea level
in the coming decades depends on the discharge from glaciers at its edges and on the surface mass balance, which is the balance between snow accumulation and surface melt. Estimates of Greenland surface mass balance increasingly utilize climate reanalyses and high-resolution regional climate models to determine snow accumulation, surface melt and runoff/refreeze. These models show significant, and model-dependent, biases (differences from observations) along the steep edges of the Greenland Ice Sheet where the highest and most variable (in space and time) rates of accumulation and surface melt are observed. Thus, the edges of the Greenland Ice Sheet are in critical need of updated accumulation
and melt data to validate models and improve mass balance estimates. The investigators propose a traverse in the Western Greenland percolation zone over two field seasons to develop continuous in-situ snow accumulation and firn density records using ground-based radar and shallow firn cores. The research objectives include: (1) determining the patterns, in time and space, of snow accumulation in Western Greenland over the past 20-40 years; (2) evaluating surface melt refreeze and englacial meltwater storage in the Western Greenland percolation
zone over the past 20-40 years; and (3) quantifying the accumulation and surface melt biases of the most recent climate reanalysis models and their regional climate model counterparts.This project will advance knowledge and understanding by providing in-situ validation observations for both the mass gain (snow accumulation) and mass loss (surface melt) components of Western Greenland surface mass balance. The western edge of the Greenland Ice Sheet has been losing mass at an accelerating rate since 2005, due mostly to decreasing surface mass balance. However, surface mass balance trends derived from regional climate models differ by a factor of ~2.5 in this region. Western Greenland firn core accumulation records, required for model validation, generally end in 1996-1998, before the most recent period of accelerated mass loss. The investigators will develop continuous records of Western Greenland snow accumulation over the last 20-40 years using ground-penetrating radar validated by frequent snow pits and
firn cores (25-30 m) analyzed for chemistry. They also propose to use a multi-offset radar method to calculate continuous firn density
data, providing a means to assess past surface melt, refreeze and current meltwater storage
in glacier aquifers. Meltwater refreeze shows the largest variability in regional climate
models among surface mass balance components, and thus validation observations are critically needed. The traverse route will crisscross the percolation zone, near-parallel to the steepest accumulation and surface melt gradients, which will increase the value of the dataset for model validation. The traverse will overlap previous traverse routes and reoccupy previously sampled sites to update firn core accumulation records by 18-20 years. In addition, the project will collect cores from new sites in data-poor regions at lower elevations, where both accumulation and surface melt increase and regional climate model validation is most needed. Surface mass balance validation of several climate reanalysis models will lead to more accurate assessments
of current and future Greenland Ice Sheet mass balance trends, which is critical for accurately predicting
future sea-level rise. The project will integrate research with student
learning at multiple levels, with an emphasis on the participation of students from underrepresented groups. The project will fund four graduate students, and incorporate numerous undergraduate researchers recruited through successful programs like the Dartmouth Women in Science Project and the Diversity in Undergraduate Geoscience Alliance. K-12 students will be engaged in this project through inquiry-based, web-hosted climate lessons incorporating the University of Maine Climate Reanalyzer and Environmental Change Model, and through field-based programs in the Boise Mountains focused on snow science. The PIs will continue their active public outreach through established and successful programs like the monthly Upper Valley Science Pub and the biannual Snow Day at the Discovery Center of Idaho, in addition to their frequent public presentations and media interviews through their respective Public Affairs offices.