Obliquity-paced Pliocene West Antarctic ice sheet oscillations
Obliquity-paced Pliocene West Antarctic ice sheet oscillations
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DOI：
10.1038/nature07867
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发表时间：
2009-03-19
期刊：
影响因子：
64.8
通讯作者：
Williams, T.
中科院分区：
文献类型：
--
作者：
Naish, T.;Powell, R.;Williams, T.
在海洋沉积物中沉积的微化石的氧同位素记录证实了地球轨道几何形状的变化控制冰河时代的假设（1）30年后，南极冰盖对轨道周期的响应仍然存在根本问题（2）。此外，需要了解“比现在更温暖”的上新世早期（类似于500 - 300万年前）期间海洋西南极冰盖（WAIS）的行为，以更好地限制未来全球变暖背景下冰盖行为的可能范围（3）。在这里，我们提出了一个海洋冰川记录从上部600米的AND-1B沉积物芯从罗斯冰架的西北部下面的ANDRILL计划，并证明了良好的日期，类似于40-kyr的周期变化的冰盖范围链接到周期的日照影响地球的轴向倾斜（倾斜度）的变化在上新世。我们的数据为轨道引起的WAIS振荡提供了直接证据，WAIS周期性地崩溃，导致从地面冰或冰架转换到罗斯湾的开放沃茨，当时行星温度比今天高出3摄氏度（4），大气CO2浓度高达400 p. p. m。v.（参考文献5、6）。这些证据与一个新的冰盖/冰架模型（7）相一致，该模型模拟了与WAIS损失相关的相当于海平面的南极冰量波动高达+7 m，以及东南极冰盖相当于海平面的波动高达+3 m，以响应海洋引起的融化。在间冰期，冰质沉积物表明地表水的生产力很高，夏季海冰最少，气温高于冰点，这表明在CO2升高的条件下，地表融化的额外影响。
Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages(1), fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles(2). Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (similar to 5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming(3). Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, similar to 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to similar to 3 degrees C warmer than today(4) and atmospheric CO2 concentration was as high as similar to 400 p. p. m. v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model(7) that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt(8) under conditions of elevated CO2.