Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma
Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma
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DOI：
10.5194/cp-13-959-2017
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发表时间：
2017-07-27
影响因子：
4.3
通讯作者：
Fogwill, Christopher J.
中科院分区：
文献类型：
--
作者：
Golledge, Nicholas R.;Thomas, Zoe A.;Fogwill, Christopher J.
南极冰盖在过去温暖时期的几何形状很难从地质证据中确定，但很重要，因为这样的重建可以更完整地了解冰盖系统如何应对气候变化。在这里，我们调查南极洲的轨道和温室气体的条件下，代表了间冰期在上新世早期在4.23马，当南半球的日照达到最大值。使用离线耦合的气候和冰盖模型，以及一个新的合成高纬度古环境代理数据来定义一个可能的气候包络线，我们模拟了一系列冰盖的几何形状，并计算它们可能对海平面的贡献。此外，我们使用这些模拟调查的过程中，西部和东部南极冰盖的环境强迫和时间尺度，这些行为表现。我们的结论是，南极冰盖贡献了8.6 +/- 2.8米的全球海平面在这个时候，在大气中的二氧化碳浓度相同的目前（400 ppm）。几个世纪以来，比现在更温暖的海洋温度导致了西南极洲的崩溃，而更高的空气温度引发了东南极洲部分地区的表面融化，在一到两千年的时间里，导致冰盖表面降低，一些地区的接地边缘漂浮，冰盖退缩到威尔克斯冰下盆地。结果表明，气候、冰盖几何形状和地形的区域变化产生了长期的海平面贡献，这些海平面贡献相对于所施加的强迫是非线性的，并且在某些条件下表现出与行为临界点相关的阈值行为。
The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offline-coupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of ice-sheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 +/- 2.8 m to global sea level at this time, under an atmospheric CO2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography pro-duce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.