Instability of the East Antartic Ice Sheet during the Pliocene warmth?

气候系统的变暖是明确的，从观测到的全球平均空气和海洋温度的上升是显而易见的。根据政府间气候变化专门委员会2007年诺贝尔和平奖获奖报告中发表的预测，到本世纪末，地球表面的温度预计将上升1.8至4.0摄氏度。现在，我们已经观察到高山冰川的退缩，北冰洋海冰的有限范围，以及格陵兰岛和南极洲部分地区极地冰盖边缘的融化。预计到2100年海平面将上升0.2到0.6米。然而，这一范围不包括冰盖的潜在贡献，如今冰盖所束缚的水团相当于60-70米的海平面变化。从过去对气候的研究中，我们知道极地冰盖会随着气候条件的变化而变化。上一次地球气候比今天明显温暖，而且持续时间较长，是在450万到300万年前的上新世时期。在温暖的上新世，全球气温比现在高出3摄氏度。这一时期的海平面估计范围比今天高5到40米，最常用的值在25米左右。如此高的海平面不仅意味着格陵兰岛和南极西部冰盖的消失，还意味着巨大的南极东部冰盖部分地区的不稳定。然而，数据很少，关于融化是否只发生在更脆弱的南极西部冰盖，还是也发生在较大的南极东部冰盖的部分地区，模型给出了相互矛盾的结果。通过我们的项目，我们将试图解决这个难题。我们将分析来自东南极洲外的南大洋的浮冰沉积物的化学成分。这种物质是由冰山带到它的沉积地点的，它的地球化学指纹包含在矿物颗粒中，使我们能够追溯到冰山来自大陆的确切区域。这反过来告诉我们，过去哪一部分冰缘变得不稳定。这些来自地质记录的证据对于检验和完善现有的气候模型至关重要。我们将研究必须对气候模式进行哪些调整才能重现我们的观测数据。一旦我们成功地建立了一个更好的数据库来了解上新世变暖期间的冰范围，一旦我们有了一个与过去观测相匹配的气候模型，我们就应该有更高的信心使用相同类型的模型来预测未来可能发生的事情。

Warming of the climate system is unequivocal, and evident from observations of increases in global average air and ocean temperatures. Based on projections published in the Nobel Peace Prize winning report of the Intergovernmental Panel on Climate Change in 2007, the Earth's surface is estimated to warm between 1.8 to 4.0 degree Celsius by the end of the century. Already now, we are observing the retreat of mountain glaciers, limited extent of sea ice in the Arctic Ocean, and melting around the edges of the polar ice caps in Greenland and parts of Antarctica. Projected sea level rise by 2100 ranges between 0.2 and 0.6 m. This range however does not include potential contributions from the ice caps, which today tie up a water mass equivalent to about 60-70 m of sea level change. From studying the climate in the past, we know that the polar ice caps can wax and wane with changing climatic conditions. The last time Earth climate was significantly warmer than today, for an extended amount of time, was 4.5 to 3 million years ago, during the time period of the Pliocene. Global temperatures in the warm Pliocene were about 3 degree Celsius higher than today. Sea level estimates for this time range from 5 to 40 m higher than today, with a most commonly used value around 25 m. Such an elevated sea level would not only mean the disappearance of the Greenland and West Antarctic ice sheets, but also instability in parts of the massive East Antarctic ice sheet. Data are however sparse, and models give conflicting results on whether melting only acted on the more vulnerable West Antarctic ice sheet, or also on parts of the large East Antarctic ice sheet. With our project we will try to address exactly this dilemma. We are going to analyse the chemical composition of ice-rafted sediments from the Southern Ocean off East Antarctica. This material was carried to its place of deposition by icebergs, and its geochemical fingerprint contained in mineral grains, allows us to track back the exact area of the continent where the iceberg was coming from. This in turn tells us which part of the ice margin became instable in the past. It is such evidence from the geological record that is vital to test and refine existing climate models. We will investigate which adjustments have to be made to climate models to reproduce our observational data. Once we succeed to produce a better database for understanding ice extent during the Pliocene warmth, and once we have a climate model that matches the observations of the past, we should have higher confidence to use the same type of model to foresee what may happen in the future.