Isotopic constraints on past ozone layer in polar ice (ISOL-ICE)

臭氧层保护所有陆地生命形式免受有害的紫外线辐射;并间接影响地球表面的气候，包括温度和风，特别是在两极附近。自1970年代后期以来，用于冰箱和喷雾罐的人造卤化碳被释放到大气中，对臭氧层造成了严重破坏，特别是在春季期间在南极洲上空。由于1989年《蒙特利尔议定书》禁止使用许多卤化碳，预计臭氧层将在本世纪内恢复到1960年代和1970年代初的状况，然而，臭氧层的厚度也受到自然原因的影响，这些原因尚不清楚，因此对未来臭氧和气候的预测不太确定。自然原因包括太阳活动的变化、火山爆发、生物源卤烃的释放和大气环流。目前，关于臭氧层在历史时间尺度上的自然变化的信息很少，即在世纪初开始直接观测之前。然而，要评估气候和臭氧政策选择的有效性，就必须了解臭氧层的自然变异性及其根本原因。为了改进对地面紫外线辐射的预测也是必要的，因为紫外线辐射被认为是一种环境致癌物，是人类健康的一个主要问题，一种超越现代测量时代的方法是使用在极地冰芯中测量的替代物。除了最近提出的生物标志物，没有过去紫外线辐射的定量代理。在这里，我们建议测量极地冰中硝酸根离子中氮和氧的同位素，以重建过去的紫外线辐射，从而重建臭氧层。同位素是相同元素的原子，具有相同数量的质子，但不同数量的中子。在南极洲内部非常干燥的地区，雪在被降雪掩埋之前暴露在阳光下好几个月。在暴露期间，雪中的硝酸盐被太阳紫外线辐射分解;在此过程中，硝酸盐中较重的氮同位素被观察到优先留在雪中，而较轻的则逃逸到上面的大气中。这种分离取决于紫外线辐射的波长和持续时间。我们假设一旦雪中的硝酸盐被深埋，它会保留向下流动的紫外辐射的同位素指纹，从而保留臭氧层厚度的同位素指纹。我们建议从东南极高原采集一个浅冰芯，那里的积累率很低，以开发和应用一个新的冰芯替代物，在过去的一千年里，限制南极上空臭氧层的趋势。为了做到这一点，我们将校准的冰芯信号与自20世纪50年代以来的南极洲上空的臭氧层的观测，然后外推到更遥远的过去的关系，使用数值模型，我们将调查冰芯的基础上重建过去的臭氧层的变化的根本原因。我们将试图回答的具体问题包括：平流层臭氧在过去是否发生了变化;以及太阳的变化、卤烃的自然排放或火山爆发是如何促成重建趋势的？

The ozone layer shields all land-based life forms from harmful ultraviolet radiation; and indirectly influences the climate at the Earth's surface, including temperature and winds, particularly near the poles. Man-made halocarbons, used for example in refrigerators and spray cans, were released to the atmosphere and have caused significant destruction of the ozone layer since the late 1970s, especially above Antarctica during spring-time. Because the use of many halocarbons was banned by the 1989 Montreal Protocol, the ozone layer is expected to recover to the conditions of the 1960s and early 1970s within this century.However, the thickness of the ozone layer is also influenced by natural causes, which are less well understood and which make predictions of future ozone and climate less certain. Natural causes include variations in the sun's activity, volcanic eruptions, release of biogenic halocarbons and atmospheric circulation. Currently there is very little information on the natural variability of the ozone layer over historic time scales, i.e. before direct observations started in the early 20th century. However, understanding the natural variability of the ozone layer and the underlying causes is necessary to evaluate the effectiveness of climate and ozone policy options. It is also necessary in order to improve predictions of ground level UV radiation, which is recognized as an environmental carcinogen and a major concern for human health.One way to go back in time beyond the era of modern measurements is the use of proxies measured in polar ice cores. Apart from a recently proposed biomarker there are no quantitative proxies of past UV radiation. Here we propose to measure the isotopes of nitrogen and oxygen in the nitrate ion in polar ice to reconstruct past ultraviolet radiation and therefore the ozone layer. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. In the very dry regions of inner Antarctica snow is exposed to sunlight for many months before being buried by snowfall. During that exposure the nitrate in the snow is decomposed by solar UV radiation; during that process the heavier nitrogen isotopes in nitrate are observed to stay preferentially in the snow, whereas the lighter ones escape to the atmosphere above. That fractionation depends on the wavelength and duration of the UV radiation. We hypothesize that once the nitrate in snow is buried at depth, it preserves an isotopic fingerprint of down-welling UV radiation and therefore of the thickness of the ozone layer.We propose to collect a shallow ice core from East Antarctic Plateau, where low accumulation rates prevail, to develop and apply a new ice core proxy based on the stable isotopes of nitrate, to constrain trends in the ozone layer above Antarctica over the last 1kyr. To do this, we will calibrate the ice core signal with observations of the ozone layer above Antarctica since the 1950s, and then extrapolate that relationship to the more distant past.Using numerical models we will investigate the underlying causes of the ice core based reconstruction of past variability in the ozone layer. Particular questions we will attempt to answer include: has stratospheric ozone changed in the past; and how did solar variability, natural emissions of halocarbons, or volcanic eruptions contribute to the reconstructed trends?