Calculating the rate of Antarctic Bottom Water formation using new theory, fine-scale modelling and observations

地球赤道地区比极地地区接收到更多的太阳能。额外的热量通过大气和海洋的环流以大约相等的比例向极地输送。温暖的地表水进入极地地区，在那里释放热量。当这些地表水冷却时，它们会开始冻结形成海冰，并将密集的盐水释放到海洋中。表面冷却和卤水释放的结合使地表水变得足够稠密而下沉。这样形成的冷底水随后向赤道流动，平衡了向极地流动的水面。底水产生的位置和机制影响海洋环流的空间分布和强度，从而决定天气。来自气候模式和观测的证据表明，南极洲周围的底水形成将受到全球变暖的影响，并将影响南半球和北半球的气候和天气。为了准确预测未来的气候变化，气候模式需要充分反映南极洲周围底部水的形成情况，而这是目前所缺乏的。由于其有限的空间分辨率和简化的物理性质，气候模式不能充分代表负责形成底水的小尺度过程。气候模型通常产生的底层水太少，而这些水又太温暖、太新鲜，这被归因于冬季海水结冰形成海冰的代表性不足，海冰将盐水释放到上层海洋。这项建议将使用海冰和海洋的高分辨率数值模拟，结合实地观测，以提高我们对控制南极洲周围底部水形成过程的理解。我们将把重点放在Ronne冰架以北的大陆架上的一个特定区域，因为这个区域被认为是南极洲周围形成的大约三分之一的底部水的来源，是南极洲周围形成底部水的其他区域的代表，因为，相对于南大洋的其他地区，我们有很多数据可以用来测试我们的模型。我们将探索Ronne polynya的作用，Ronne polynya是由南极洲吹来的风造成的海冰覆盖的开放水域，以及巴西冰的形成，在控制该地区底部水的形成方面。巴西的冰由毫米大小的冰晶组成，这些冰晶是海水低于冰点时形成和生长的。我们将把巴西冰形成的物理学纳入我们的模型。我们将用最近获得的海洋学和大气数据以及卫星观测来检验我们的模型。我们将使用我们的模型，这将是迄今为止物理上最复杂和高度校准的模型，来计算罗纳大陆架底部水形成的速度。这些模型一旦针对罗纳大陆架进行了校准，就将用于计算整个南极洲周围的海底形成总量。除了对底水形成的新估计外，我们将开发新的物理模型并确定海洋混合的最佳表示。

The equatorial regions of the Earth receive more solar energy than the polar regions. The extra heat is transported polewards in approximately equal parts by the circulations of the atmosphere and ocean. Warm surface waters enter the polar regions, where they release their heat. As these surface waters cool, they can begin to freeze to form sea ice and this releases dense brine into the ocean. The combination of surface cooling and brine release causes the surface waters to become sufficiently dense to sink. The cold bottom waters so formed then flow equatorward, balancing the poleward surface flow. The location and mechanism of bottom water production affects the spatial distribution and intensity of the ocean circulation, which helps determine the weather.Evidence from climate models and observations suggest that bottom water formation around Antarctica will be affected by global warming and will influence the climate and weather in both the Southern and Northern hemispheres. In order to accurately predict future climate change, climate models require an adequate representation of bottom water formation around Antarctica, which is presently lacking. As a result of their limited spatial resolution and simplified physics, climate models are unable to represent adequately the small-scale processes responsible for the formation of bottom water. Climate models typically produce too little bottom water and this water is too warm and fresh, which has been ascribed to inadequate representation of winter freezing of seawater to form sea ice, which releases brine into the upper ocean. This proposal will use high resolution numerical modelling of the sea ice and ocean, combined with field observations to improve our understanding of the processes controlling bottom water formation around Antarctica.We will focus on a particular region, over the continental shelf north of the Ronne Ice Shelf, since this region is believed to be responsible for about a third of the bottom water formed around Antarctica, is representative of other regions of bottom water formation around Antarctica, and because, relative to other areas in the Southern Ocean, we have a lot of data with which to test our model. We will explore the role of the Ronne polynya, an open water region in the sea-ice cover caused by winds blowing off Antarctica, and frazil ice formation, in controlling the bottom water formation in this region. Frazil ice consists of millimetre-sized ice crystals that form and grow when the seawater is below its freezing point. We will include the physics of frazil ice formation into our models. We will test our models with recently-acquired oceanographic and atmospheric data and satellite observations. We will use our models, which will be the most physically-sophisticated, and highly-calibrated, models to date, to calculate the rate of bottom water formation over the Ronne continental shelf. The models, once calibrated for the Ronne continental shelf, will be used to calculate total bottom formation around the whole of Antarctica. In addition to new estimates for bottom water formation, we will develop new model physics and identify the optimal representation of ocean mixing.