Present and Future Stability of Larsen C Ice Shelf (SOLIS)

1995年和2002年被广泛报道的南极半岛拉森A和B冰架的迅速崩解是气候变化对这一地区产生巨大影响的非同寻常的例证。冰架破裂引起科学和公众的特别关注，主要原因有两个：[a]冰架主要由来自冰川和冰流(将冰从冰盖内部输送到边缘的密闭、快速流动的‘传送带’)的冰流入来维持。随着冰架坍塌导致的支撑力被移除，这些冰川和冰流可能会加速，从而增加从冰盖内部向海洋的流量。这可能会导致这些冰盖的快速和持续收缩，以及海平面的同样戏剧性上升。[b]除了由于[a]而加速了冷融水的输入，冰架的解体还可能导致区域海洋环流格局的改变和南极底水的形成。AABW是全球海洋环流的重要贡献者，而全球海洋环流反过来又调节着世界范围的气候。如果AABW形成的改变可以触发这种环流的变化，那么冰架坍塌可能间接地导致全球气候模式的改变。如果南极半岛的气候变暖速度继续异常高(目前约为每世纪4摄氏度)，该地区剩余冰架的稳定性就会受到质疑。拉森C冰架是南极半岛上最大的冰架，也是2002年坍塌的拉森B冰架的南部邻居，在过去的15年里，拉森C冰架逐渐变薄。这可能表明拉森C冰架已经进入了退缩或可能崩塌的过程。如果冰架解体(甚至部分解体)，在这一次事件中损失的冰架很可能比南极半岛之前所有事件加起来的冰架损失的总和还要多。因此，关键问题是：拉森C冰架未来有可能坍塌吗？拟议的项目旨在回答这个问题。冰架的稳定性受一系列冰内部控制因素的控制，包括：[a]冰的成分和结构；[b)应力强度(作为去稳定力)和冰的断裂韧性(冰抵抗应力从而起到稳定力的能力)之间的平衡；以及[c]裂谷的模式和过程。气候变化不仅可以直接迫使内部控制，也可以通过一系列外部控制(物质平衡和冰架总厚度；冰架几何形状；海洋和海冰过程；气象学)间接地迫使内部控制。在确定内部控制的特点以及模拟气候条件的直接和间接强迫(通过外部控制)方面，我们提议采用一个三级战略：(A)使用标准地球物理方法进行实地调查，作为提供所需地面控制的项目的核心活动；(B)利用已有的遥感技术将实地数据扩大到整个冰架；以及(C)利用扩大的数据强迫调整后的计算机模型(以前成功地应用于Filchner-Ronne和Larsen B冰架)。模型输出将允许[a]确定拉森C冰架目前有多稳定；[b]模拟一系列未来情景，包括冰架迅速后退或解体；以及[c]确定最现实的未来情景。这将使我们能够得出拉森C冰架未来是否可能坍塌的结论。

The widely publicised rapid disintegrations of the Larsen A and B ice shelves on the Antarctic Peninsula in 1995 and 2002 were extraordinary demonstrations of the dramatic impact that climatic changes can have on this region. Ice shelf break-up is of particular scientific and public concern for two main reasons: [a] Ice shelves are sustained principally by inflow of ice from glaciers and ice streams (confined, fast-flowing 'conveyor belts' that transport ice from the interior of ice sheets to their margins). As the buttressing force is removed as a result of ice shelf collapse, these glaciers and ice streams can speed up and thus increase discharge from the ice sheet interior to the ocean. This could potentially lead to rapid and sustained shrinkage of these ice sheets and an equally dramatic increase in sea level. [b] In addition to accelerated input of cold melt water as a result of [a], ice shelf disintegration may also lead to modification of regional patterns of ocean circulation and the formation of Antarctic Bottom Water (AABW). AABW is an important contributor to the global ocean circulation which in turn regulates world-wide climate. If modification of AABW formation can trigger changes in this circulation, ice shelf collapse could indirectly contribute to alterations of world-wide climate patterns. If rates of climatic warming on the Antarctic Peninsula continue to be anomalously high (presently ~ 4 degrees C per century), the stability of the remaining ice shelves in this region comes into question. Larsen C, as the largest ice shelf on the Antarctic Peninsula and the southern neighbour of Larsen B which collapsed in 2002, has thinned progressively over the past 15 years. This could indicate that the Larsen C ice shelf has already entered a process of retreat or possibly collapse. If the ice shelf were to disintegrate (even partially), it is likely that more shelf ice would be lost in this single incident than has been lost by all previous incidents on the Antarctic Peninsula taken together. The key question is therefore: Is the Larsen C ice shelf likely to collapse in the future? The proposed project aims to answer that question. The stability of an ice shelf is controlled by a range of ice-internal controls, including [a] ice composition and structure; [b] the balance between stress intensity (acting as a de-stabilising force) and ice fracture toughness (the ability of ice to resist stress, thus acting as a stabilising force); and [c] patterns and processes of rifting. Climatic changes can force the internal controls not only directly but also indirectly via a range of external controls (mass balance and thus total ice shelf thickness; ice shelf geometry; oceanographic and sea ice processes; meteorology). In characterising the internal controls and modelling direct and indirect (via the external controls) forcing by climatic conditions, we propose to adopt a three-tier strategy: [a] field-based investigations using standard geophysical methods as the core activity of the project providing the required ground control; [b] upscaling of the field data to the whole ice shelf using established remote sensing techniques; and [c] forcing of an adapted computer model (previously applied successfully to the Filchner-Ronne and Larsen B ice shelves) using the upscaled data. The model outputs will allow [a] identification of how stable the Larsen C ice shelf is at present; [b] simulation of a range of future scenarios including rapid ice shelf retreat or disintegration; and [c] identification of the most realistic future scenario. This will enable us to conclude whether the Larsen C ice shelf is likely to collapse in the future.