Walsh Amber, Ball Thomas, Schultz David M
School of Physics and Astronomy, University of Manchester, Manchester, UK.
Department of Meteorology, University of Reading, Reading, UK.
Sci Rep. 2019 Feb 20;9(1):2349. doi: 10.1038/s41598-019-38839-6.
During the PaleoProterozoic 2.45 to 2.2 billion years ago, several glaciations may have produced Snowball Earths. These glacial cycles occurred during large environmental change when atmospheric oxygen was increasing, a supercontinent was assembled from numerous landmasses, and collisions between these landmasses formed mountain ranges. Despite uncertainties in the composition of the atmosphere and reconstruction of the landmasses, paleoclimate model simulations can test the sensitivity of the climate to producing a Snowball Earth. Here we present a series of simulations that vary the atmospheric methane concentration and latitudes of west-east-oriented mountain ranges on an idealised supercontinent. For a given methane concentration, the latitudes of mountains control whether a Snowball Earth forms or not. Significantly, mountains in middle latitudes inhibited Snowball Earth formation, and mountains in low latitudes promoted Snowball Earth formation, with the supercontinent with mountains at ±30° being most conducive to forming a Snowball Earth because of reduced albedo at low latitudes. We propose that the extreme sensitivity of a Snowball Earth to reconstructions of the paleogeography and paleoatmospheric composition may explain the observed glaciations, demonstrating the importance of high-quality reconstructions to improved understanding of this early period in Earth's history.
在24.5亿至22亿年前的古元古代，几次冰川作用可能造就了雪球地球。这些冰川周期发生在大规模环境变化期间，当时大气中的氧气在增加，一个超级大陆由众多陆地聚合而成，这些陆地之间的碰撞形成了山脉。尽管大气成分和陆块重建存在不确定性，但古气候模型模拟可以测试气候对产生雪球地球的敏感性。在这里，我们展示了一系列模拟，这些模拟在一个理想化的超级大陆上改变大气甲烷浓度和东西走向山脉的纬度。对于给定的甲烷浓度，山脉的纬度控制着雪球地球是否形成。重要的是，中纬度地区的山脉抑制了雪球地球的形成，而低纬度地区的山脉促进了雪球地球的形成，由于低纬度地区反照率降低，位于±30°的有山脉的超级大陆最有利于形成雪球地球。我们认为，雪球地球对古地理和古大气成分重建的极端敏感性可能解释了观测到的冰川作用，这表明高质量的重建对于增进对地球历史这一早期阶段的理解至关重要。
