Investigating Hydrologic Loading in Southeast Alaska Using GRACE and GPS Data

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。阿拉斯加东南部沿海和加拿大邻近地区的冰川和冰原是地球上最具活力的冰川和冰原之一，由于气候变暖和潮水冰川消退的动态，它们正在以惊人的速度融化。这一地区的冰川消融始于小冰期的结束，并持续到今天，海平面上升，产生了戏剧性的隆起和重力变化。今天？S壮观的冰川湾是从1800年左右开始的冰川潮水快速退缩形成的；一些地方原本超过1公里厚的冰川在几十年内消失了，它们的冰流入了海洋。当冰的重量被移除时，陆地会上升，这很容易通过全球定位系统(GPS)的精确测量来测量，并导致地球重力场的变化，这些重力场可以在地表或从太空测量。然而，冰期后的隆升并不是以稳定的速度发生的；整个冬季，地面略有下沉，然后从春季融化开始迅速隆起，直到下一个冬季再次开始下沉。这些变化是由水文负荷主导的，主要是由于冰雪的季节性积累和融化。这里的季节变化比大型水文模型预测的要大，后者没有很好地解释冰雪。这项研究的调查人员将观察陆地表面高度和重力的变化，并利用这些测量结果建立该区域水、雪和冰质量变化的区域模型，并与日本东北大学的科学家和美国宇航局戈达德航天飞行中心的Scott Luthcke合作进行这些测量和建模。包括日本同事的绝对重力测量，他们将测试和改进地区性GIA模型，并测试隆升速度是否随着最近冰质量损失率的增加而加快。他们将继续与我们的日本同事一起运行6个GPS站点，对GPS(包括PBO)和GRACE数据进行分析和建模，并将开发GRACE数据时间跨度的水文负荷变化的区域模型，并使用更长的GPS时间序列将该模型向后扩展。与美国宇航局的全球陆地数据同化系统等大型水文模型相比，水文负荷模型可能代表着一大进步，后者在阿拉斯加等数据匮乏的地区很难限制。这个项目将提高我们对阿拉斯加东南部水文学的理解。向阿拉斯加湾排放淡水会影响海洋生物栖息地，并可能改变阿拉斯加沿岸洋流的模式。该模型将提供有关径流分布和时间的新信息，这对海洋学和生物学研究很重要，并将作为海洋盐度模型和栖息地分布模型的补充投入。GRACE、GPS数据和水文模型的组合方法将为这些方法在其他地区的应用提供一个模板。最终，这些方法将为冰川对海平面上升的贡献提供更准确的估计。他们将继续向公众和国家公园管理局工作人员通报研究结果，这项工作将为他们提供有关该地区积雪和融化的规模和分布的新信息。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The glaciers and icefields of coastal southeast Alaska and the adjacent areas of Canada are among the most dynamic on the planet, and they are shedding mass at a dramatic rate due to climate warming and the dynamics of tidewater glacier retreat. Deglaciation of this region began with the end of the Little Ice Age, and continues today, raising sea level and producing dramatic uplift and gravity change. Today?s spectacular Glacier Bay was created by the rapid tidewater retreat of glaciers beginning around 1800; glaciers originally well over 1 km thick in places disappeared in a few decades, with their ice discharged into the ocean. The land rises up as the weight of the ice is removed, causing uplift easily measured by precise surveying using the Global Positioning System (GPS), and causing changes in Earth's gravity field that can be measured at the surface or from space. However, post-glacial uplift does not occur at a steady rate; the ground subsides slightly throughout the winter before uplifting rapidly from the onset of the spring melt until subsidence begins again the next winter. These variations are dominated by hydrological loading, mainly due to the seasonal accumulation and melting of snow and ice. The seasonal variations here are larger than predicted by large-scale hydrologic models, which do not account for snow and ice well. The investigators of this study will look at variations in height of the land surface and of gravity, and use these measurements to develop regional models of the changes in mass of water, snow and ice in the region and carry out these measurements and modeling in collaboration with scientists at Tohoku University (Japan), and Scott Luthcke at NASA Goddard Space Flight Center. Including absolute gravity measurements, made by the Japanese colleagues, they will test and refine regional GIA models, and test whether the uplift rates are accelerating with the recent increase in ice mass loss rate. They will continue operation of 6 GPS sites installed with our Japanese colleagues, analysis and modeling of the GPS (including PBO) and GRACE data, and will develop a regional model of hydrological load variations for the time span of GRACE data, and extend the model back in time using the longer GPS time series. The hydrological load model will likely represent a large improvement over large-scale hydrologic models such as NASA's Global Land Data Assimilation System, which are difficult to constrain in data-poor regions such as Alaska.This project will improve our understanding of the hydrology of southeast Alaska. Freshwater discharge into the Gulf of Alaska affects marine habitat and may alter the patterns of the Alaska coastal current. The model will provide new information on the distribution and timing of runoff, which are important for oceanographic and biological studies, and will be of value as additional input into ocean salinity models and habitat distribution models. The methods for combining GRACE, GPS data and hydrological models will provide a template for application of these approaches to other regions. Ultimately these methods will provide more accurate estimates of the glacier contribution to rising sea level. They will continue to inform the public and National Park Service personnel of research results, and this work will provide new information to them about the magnitude and distribution of snow accumulation and melt in the region.