The role of atmospheric forcing on the dynamic stability of Greenland's outlet glaciers

该项目将量化地面产生的融水波动对格陵兰冰盖(GRIS)边缘冰运动的影响。更具体地说，它将提供数据，使冰盖模型师能够改进他们对未来全球变暖导致海平面上升的影响的预测。为了实现这一目标，需要对GRIS开展专门的实地活动，以研究潮水冰川和陆地冰川沿从冰盖边缘延伸到平衡线高度(ELA)的流动平行横断面的季节性冰流动力学和径流过程。北半球最大的淡水储存量--相当于海平面上升7米--被储存在格陵兰冰盖内，然而它现在和未来对海平面的贡献受到很大限制(IPCC，2007)。最近的观测表明，由于表面熔化增加(例如Steffen等人，2004年)和动态变薄(例如Rignot和Kanagaratnam，2006)，地球表面边缘附近的质量损失正在加速。然而，控制动态变薄的关键过程尚未确定(Alley等人，2005年)，因此，作为IPCC海平面预测基础的冰盖模型没有纳入其中。这在一定程度上反映了这样一个事实，即揭示冰川普遍加速的卫星数据不能以解决原因机制所需的时间分辨率获得。我们目前对GRIS质量平衡的理解尤其复杂，因为冰缘动力学对冰川上融水渗透到冰床所引起的融水润滑变化的敏感度存在不确定性(Zwally等人，2002年)。最近对GRIS Shepherd等人的观察显示，在7月份的5天时间里，地表水文和动力学之间存在强烈而直接的耦合，其中&gt；100%的日速度发生日波动，最大日速度随温度变化。这类观测证实，需要以全年高时间(分小时)和空间分辨率获取水文和动态数据，以确定冰融化和流动之间的耦合参数。该项目将以必要的分辨率收集数据，以量化融化水生产和冰盖动态之间的关系，从而使冰盖建模人员能够改进对全球观测系统对气候变化的反应的预测。我们将沿着GRIS西缘的两个平行流动的横断面进行地面实验，以解决以下目标：1.与冰上排水系统(包括冰上湖泊)的季节性演变有关的水文-动力联系是否存在时间和空间模式？2.地表产生的融水渗透到冰盖底部的区域？3.冰川表面输入的融水数量与动态响应的大小之间是否存在关系？4.在融化季节期间，潮水和陆地终止冰川的行为是否不同？将在2009年和2010年开展实地活动，以确定：1)融化的速度、范围和持续时间。2)冰上湖泊中储存和释放的水量以及输送到自由排水小丘的水量的时间和空间变化。3)冰动力的季节变化、日变化和小时变化。4)冰川流量和水化学变化(拉塞尔冰川)。作为我们工作的结果，将有可能确定GRIS边缘的冰动力学是否受到地表融水排出后冰床润滑的显著影响。我们的结果将被提供给冰盖模型师，以帮助他们限制对GRIS未来的预测

This project will quantify the effect of surface generated melt-water fluctuations on ice motion at the margin of the Greenland Ice Sheet (GrIS). More specifically, it will provide data that will enable ice-sheet modellers to improve their predictions of the future contribution of the GrIS to sea level rise in response to a warming world. To achieve this aim requires a dedicated field campaign to the GrIS to investigate seasonal ice flow dynamics and runoff processes along flow parallel transects extending from the ice sheet margin to the equilibrium line altitude (ELA) at both tidewater and land-terminating glaciers. The greatest store of fresh water in the northern hemisphere - equivalent to 7m of eustatic sea level rise - is held within the Greenland Ice Sheet (GrIS), and yet its present and future contribution to sea level is poorly constrained (IPCC, 2007). Recent observations suggest that mass loss near the margin of the GrIS is accelerating through a combination of increased surface melting (e.g. Steffen et al, 2004) and dynamic thinning (e.g. Rignot and Kanagaratnam, 2006). However, the key processes controlling dynamic thinning have yet to be identified (Alley et al, 2005), and in consequence, are not incorporated in the ice-sheet models which form the basis of the IPCC sea level projections. This in part reflects the fact that the satellite data that has revealed the widespread speed-up of glaciers cannot be acquired at the temporal resolution needed to resolve the causal mechanisms. Our present understanding of GrIS mass balance is especially complicated by uncertainties in the sensitivity of ice-marginal dynamics to changes in melt-water induced lubrication resulting from penetration of supraglacial melt-waters to the glacier bed (Zwally et al, 2002). Recent observations on the GrIS Shepherd et al, in review) reveal, over a five day period in July, a strong and direct coupling between surface hydrology and dynamics where diurnal fluctuations in velocity of >100% occur and where maximum daily velocities scale with temperature. Such observations confirm the need to acquire hydrological and dynamic data at high temporal (sub-hourly) and spatial resolution throughout the year to parameterise the coupling between ice melting and flow. This project will collect data at the necessary resolution to quantify the relationship between melt-water production and ice sheet dynamics thereby enabling ice-sheet modellers to improve predictions of the GrIS's response to climate change. We will conduct ground based experiments along two flow-parallel transects at the western margin of the GrIS in adjacent land and marine terminating drainage basins to address the following objectives: 1. Is there a temporal and spatial pattern to any hydrology-dynamic link associated with the seasonal evolution of the supraglacial drainage system (including supraglacial lakes)? 2. Over what area does surface generated meltwater penetrate to the base of the ice sheet? 3. Is there a relationship between the volume of meltwater input at the glacier surface and the magnitude of the dynamic response? 4. Do tidewater and land-terminating glaciers behave differently during the course of a melt-season? Field campaigns will be undertaken during 2009 and 2010 to determine: 1) The rate, extent and duration of melt. 2) The temporal and spatial variations in water volumes stored in and released from supraglacial lakes and delivered to freely draining moulins. 3) The seasonal, diurnal and hourly variations in ice dynamics. 4) The variations in proglacial discharge and water chemistry (at Russell Glacier). As a result of our work, it will be possible to determine whether ice dynamics at the margin of the GrIS is significantly affected by lubrication of the glacier bed following the drainage of surface derived meltwaters. Our results will be delivered to ice sheet modellers to help them constrain predictions for the future of the GrIS