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

利用新理论、精细尺度建模和观测计算南极底层水形成率

基本信息

批准号：
NE/I023708/2
负责人：
Daniel Feltham
金额：
$ 11.62万
依托单位：
University of Reading
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FI023708%2F2
关键词：
Calculating rate Antarctic Bottom Water

项目摘要

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.

地球的赤道地区比极地地区接收更多的太阳能。多余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。当这些表层水冷却时，它们会开始冻结形成海冰，并将浓盐水释放到海洋中。表面冷却和盐水释放的结合导致地表水变得足够稠密以下沉。这样形成的冷底层水随后流向赤道，平衡了流向极地的表面流。底水产生的位置和机制影响海洋环流的空间分布和强度，从而有助于决定天气。气候模型和观测的证据表明，南极洲周围底水的形成将受到全球变暖的影响，并影响气候和气候。南半球和北半球的天气。为了准确预测未来的气候变化，气候模型需要充分反映南极洲周围底层水的形成，而目前这方面是缺乏的。由于其有限的空间分辨率和简化的物理原理，气候模型无法充分代表导致底水形成的小规模过程。气候模型通常产生的底层水太少，而且这些水太温暖和新鲜，这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。该提案将使用海冰和海洋的高分辨率数值模型，并结合实地观测，以提高我们对控制南极洲周围底层水形成过程的理解。我们将重点关注龙纳冰以北大陆架上空的特定区域由于该区域据信形成了南极洲周围约三分之一的底水，因此它代表了南极洲周围其他底水形成区域，并且因为相对于南大洋的其他区域，我们有很多底水形成区域。用于测试的数据我们的模型。我们将探讨龙恩冰间湖（由南极洲吹来的风和碎冰形成而形成的海冰覆盖中的开放水域）在控制该地区底层水形成方面的作用。冰晶由毫米大小的冰晶组成，当海水低于冰点时就会形成并生长。我们将把碎冰形成的物理学纳入我们的模型中。我们将使用最近获得的海洋学和大气数据以及卫星观测数据来测试我们的模型。我们将使用我们的模型（迄今为止物理最复杂、校准度最高的模型）来计算龙讷大陆架底层水的形成速率。这些模型一旦针对龙讷大陆架进行校准，将用于计算整个南极洲周围的总底部形成。除了对底层水形成的新估计之外，我们还将开发新的物理模型并确定海洋混合的最佳表示。