Drivers of Oceanic Change in the Amundsen Sea (DeCAdeS)

海平面上升是全球变暖最具破坏性的后果之一，威胁着世界各地的沿海人口和基础设施。如果我们要制定策略来适应或减轻这种威胁，我们需要知道未来会发生什么。在对未来海平面的估计中，最大的不确定性是巨大的南极冰盖的影响。对冰盖某些部分变薄的观测表明，一种不可逆转的变化可能已经在进行中，可能在未来几个世纪使海平面上升1米以上。冰盖变薄在阿蒙森海部分最为突出，据观察，它从海岸向内陆蔓延，并以类似的方式影响到邻近的流出冰川。这些事实表明，海洋驱动的冰川末端融化的一些变化是变化的触发因素，导致人们普遍认为，最终由全球变暖驱动的海水变暖是罪魁祸首。然而，对阿蒙森海海洋温度的观测表明，这段历史更为复杂。这些记录始于1994年，仅包括2009年之前的少量观测，但表明了以十年为周期的冷暖循环。这促使人们重新思考海洋是如何与冰盖相互作用从而产生观测到的变薄现象的。在这个项目中，我们计划利用新技术来填补阿蒙森海海洋温度变化记录的空白。我们将改造一艘机器人潜艇，使其能够在浮冰下越冬，定期测量将温水带到冰层的洋流的性质和强度。这些测量将由固定仪器进行补充，这些仪器在选定的地点连续记录，海豹携带的传感器将记录温水的深度，无论何时何地海豹潜入水面以下觅食。我们将把这些关于海面以下正在发生的事情的详细观测结果与卫星可以探测到的海面高度变化联系起来。这将使我们能够利用30多年来收集的卫星记录来推断地表下海洋过去的变化。这些结果将使我们能够确认最近的暖周期和冷周期的时间和幅度，并将它们与冰盖变薄的记录直接联系起来。为了将我们对阿蒙森海温度的了解扩展到卫星时代之后，我们将使用该地区海洋环流的数值模型来确定造成我们所观察到的温度变化的大气强迫模式。然后，我们将研究过去大气环流的重建，以生成关键大气变化的历史。最后，我们将研究区域大气环流的这些变化与全球尺度大气变化的关系，为我们提供解决过去是什么条件引发了当前的变薄以及未来可能会发生什么的问题所需的长期视角。如果我们发现最近的十年是典型的，而之前几十年的特点是类似的海洋强迫周期，我们就会表明，预测冰盖的未来需要了解它对极端事件的反应。就像为气候变化的影响做规划的海岸工程师，他们必须建造海洋防御工事，以防止风暴潮与涨潮同时产生的极端温度一样，我们需要了解阿蒙森的极端温度需要持续多长时间和多严重，才能引发冰盖变薄的事件。我们还需要知道，是什么更大规模的大气变化模式的组合在阿蒙森产生了“完美风暴”，从而使冰盖失去平衡。我们的项目将提供解决这些关键问题所需的知识。

Sea level rise is one of the most disruptive consequences of global warming, threatening coastal populations and infrastructure worldwide. If we are to develop strategies to either adapt to, or mitigate against, that threat, we need to know what to expect in the future. The biggest uncertainty in estimates of future sea level is the contribution of the vast Antarctic Ice Sheet. Observations of thinning in some parts of the ice sheet have led to suggestions that an irreversible change may already be underway that could add over a metre to sea level over the coming centuries.Thinning is most prominent in the Amundsen Sea sector of the ice sheet, where it has been observed to spread inland from the coast, and to affect neighbouring outflow glaciers in a similar way. Those facts demonstrate that some change in ocean-driven melting of the glacier termini has been the trigger of change, leading to a widespread belief that warming of the ocean waters, driven ultimately by global warming, is responsible. However, observations of ocean temperature in the Amundsen Sea suggest a more complex history. The records start in 1994, and include only a few observations prior to 2009, but suggest cycles between warm and cool conditions occurring over decadal periods. That motivates a major rethink of how the ocean interacts with the ice sheet to produce the observed thinning.In this project we plan to exploit new techniques to fill the gaps in the record of ocean temperature change in the Amundsen Sea. We will modify a robotic submarine so that it can over-winter beneath the pack ice, periodically measuring the properties and strength of the currents carrying warm water towards the ice. Those measurements will be complemented by fixed instruments that record continuously at selected locations and seal-borne sensors that will record the depth of the warm water wherever and whenever the seals dive below the surface to feed. We will relate these detailed observations of what is happening below the sea surface to changes in the height of the sea surface that can be detected by satellites. That will enable us to exploit the satellite records collected over three decades to infer past changes in the sub-surface ocean. The results will allow us to confirm the timing and magnitude of recent warm and cool cycles and relate them directly to the records of ice sheet thinning.To extend our knowledge of Amundsen Sea temperatures beyond the satellite era we will use a numerical model of the ocean circulation in the region to identify the patterns of atmospheric forcing that were responsible for the changes in temperature that we have observed. We will then examine reconstructions of the past atmospheric circulation to generate a history of the key atmospheric changes. Finally, we will investigate how those changes in the regional atmospheric circulation relate to global scale atmospheric change, providing us with the longer-term perspective that is needed to address the questions of what past conditions initiated the current thinning and what the future might hold.Should we find that the most recent decade is typical, and that earlier decades have been characterised by similar cycles in ocean forcing, we will have shown that predicting the future of the ice sheet requires an understanding of its response to extremes. Much like the coastal engineer planning for the impacts of climate change, who must construct sea defences to protect against the extreme levels generated when storm surges coincide with high tides, we need to understand how long and severe the warm extremes in the Amundsen need to be in order to trigger episodes of ice sheet thinning. We also need to know what combination of larger-scale modes of atmospheric variability produces the "perfect storm" in the Amundsen that can push the ice sheet out of balance. Our project will deliver the knowledge needed to address those critical questions.