Drivers of Oceanic Change in the Amundsen Sea (DeCAdeS)

阿蒙森海海洋变化的驱动因素 (DeCAdeS)

• 批准号: NE/T012625/1
• 负责人: Julie Jones
• 金额: $ 39.4万
• 依托单位: University of Sheffield
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FT012625%2F1
• 关键词: Drivers; Oceanic; Change; Amundsen; Sea

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.

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。如果我们要制定战略来适应或减轻这种威胁，我们需要知道未来会发生什么。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贡献。对冰盖某些部分变薄的观察表明，可能已经发生了不可逆转的变化，可能会在接下来的几个世纪里使海平面增加一米以上。冰盖的阿蒙森海部分最明显的是变薄，人们观察到它从海岸向内陆扩散，并以类似的方式影响到邻近的外流冰川。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，最终由全球变暖推动的海水变暖是罪魁祸首。然而，对阿蒙森海海洋温度的观察表明，这是一段更复杂的历史。这些记录始于1994年，只包括2009年之前的几次观测，但表明温暖和凉爽的条件之间发生了十年一遇的周期。这激发了对海洋与冰盖如何相互作用以产生观测到的厚度的重大反思。在这个项目中，我们计划开发新技术来填补阿蒙森海海洋温度变化记录中的空白。我们将改装一艘机器人潜艇，使其能够在厚厚的冰层下越冬，定期测量向冰层输送温暖水的洋流的性质和强度。这些测量将得到在选定地点连续记录的固定仪器和海豹携带的传感器的补充，这些传感器将记录无论何时何地海豹潜入海面以下觅食的温水深度。我们将把这些对海面下正在发生的事情的详细观测与卫星可以探测到的海面高度的变化联系起来。这将使我们能够利用三十年来收集的卫星记录来推断地下海洋过去的变化。这些结果将使我们能够确认最近冷暖循环的时间和大小，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洋温度的了解扩展到卫星时代以外，我们将使用该地区海洋环流的数值模型来确定导致我们观察到的温度变化的大气强迫模式。然后，我们将检查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中的这些变化如何与全球尺度的大气变化相关，为我们提供解决当前变薄的过去条件和未来可能保持的问题所需的更长期的视角。如果我们发现最近的十年是典型的，而前几十年的海洋强迫具有类似的周期，我们将表明，预测冰盖的未来需要了解其对极端情况的反应。就像计划应对气候变化影响的沿海工程师一样，他们必须建造海防，以防止风暴潮与涨潮同时产生的极端水平，我们需要了解阿蒙森地区的极端温暖需要多长时间和多严重才能引发冰盖变薄。我们还需要知道大气变化的更大尺度模式的什么组合在阿蒙森产生了可以将冰盖推向平衡的“完美风暴”。我们的项目将提供解决这些关键问题所需的知识。