Understanding the Arctic continental shelf mixing regimes and their impact on shelf sea-circulation and upper ocean stratification

了解北极大陆架混合机制及其对陆架海洋环流和上层海洋分层的影响

• 批准号: NE/H016007/1
• 负责人: Yueng-Djern Lenn
• 金额: $ 29.06万
• 依托单位: Bangor University
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH016007%2F1
• 关键词: Understanding; Arctic; continental; shelf; mixing

Rapid climate change is indisputable in the Arctic, where the record minimum sea-ice extent of September 2007 has been followed by the fastest recorded rate of sea-ice loss in August 2008 leading to near-minimum record levels again this year. A serious concern is that global climate models consistently underpredict the observed rate of Arctic climate change. A key environment in the Arctic are the continental shelf seas that account for 53% of the area covered by the Arctic Ocean and are the critical link between terrestrial and oceanic components of the earth system. There is much we still do not understand about how the energy from tides, wind, winter cooling and summertime heating can interact to mix fresh light river water with saltier sea water on the Arctic continental shelves. This gap in understanding has led to poorly parameterised shelf-sea physics in the global numerical computer models used to predict future climate. What happens in the Arctic shelf seas is tremendously important to the Arctic Ocean environment as lighter fresher shelf waters spread out into the layers of the interior basins, while denser shelf waters cascade down the continental slopes, penetrating to deeper levels where they encounter dense, warm, salty water from the Atlantic that has come from Fram Strait. The lighter cold, fresh shelf waters are thought to replenish the Arctic halocline layer that acts as critical barrier to heat fluxes from the deep warm Atlantic waters that may undermine Arctic sea-ice cover. The denser shelf waters mix with the Atlantic water at depth as it circumnavigates the Arctic Ocean, before exiting as a denser cooler fresher overflow current through the Nordic Seas. This dense Nordic Sea overflow is critical component of the global oceanic 'conveyor belt' of heat and freshwater know as the global overturning circulation that helps regulate global climate. Therefore, the Arctic shelf water production mechanisms are not just important for regional climate but also global climate. In the research proposed here, I aim to characterize mixing processes on Arctic continental shelfs, taking the important first step towards a comprehensive understanding of the Arctic earth-ocean system and improving predictions of future change and the consequences for global climate. I am interested in specific questions about how tidal energy can be used to mix water masses either by generating turbulence or by straining a vertically well-mixed but laterally differentiated water column and causing convection. Another key question I will address is how energy from the wind can be used to generate inertial oscillations that may also interact with the tide and cause mixing. These processes have been shown to be important in temperate shelf seas, but have yet to be investigated in an environment subjected to the extreme seasonal fluctuations, large riverine freshwater discharges and ice-formation-melt-cycle experienced on the Arctic continental shelves. My strategy is to use all the available data to gain an understanding of the shelf sea state and its seasonal heating and cooling cycles and then map out the different mixing regimes on the shelves, so that we can determine how, where and what kind of shelf water is being produced. These ideas will then be incorporated into a shelf-sea numerical computer model to test the sensitivity of the shelf seas system to scenarios of increasing river discharge and sea-ice loss which are resulting from climate change. This will enable us to diagnose feedbacks in the continental shelf -ocean circulation and climate system and help us improve the representation of the important shelf processes in global climate models, and ultimately, the predictions of our future climate.

在北极，快速的气候变化是无可争辩的，继2007年9月创纪录的最低海冰面积之后，2008年8月又出现了有记录以来最快的海冰消失速度，导致今年再次达到接近最低纪录的水平。一个严重的问题是，全球气候模型一直低估了北极气候变化的观测速度。北冰洋的一个关键环境是占北冰洋覆盖面积53%的大陆架海，它是连接地球系统陆地和海洋组成部分的关键纽带。关于潮汐、风、冬季降温和夏季供暖的能量如何相互作用，将北极大陆架上清淡的河水和较咸的海水混合在一起，我们仍然有许多不了解的地方。这种理解上的差距导致了用来预测未来气候的全球数值计算机模型中的陆架-海洋物理参数很差。北冰洋陆架海中发生的情况对北冰洋环境极其重要，因为更轻、更新鲜的陆架水向内陆盆地的层层扩散，而更密集的陆架水沿着大陆斜坡向下倾泻，渗透到更深的地方，在那里它们遇到来自弗拉姆海峡的来自大西洋的稠密、温暖、含盐的水。更轻、更冷、更新鲜的大陆架水域被认为补充了北极盐跃层，该层是阻止来自温暖的大西洋深层水域的热通量的关键屏障，这可能会破坏北冰洋的海冰覆盖。当大西洋环绕北冰洋航行时，密度较高的陆架水域与大西洋水在深处混合，然后以更密集、更凉爽、更新鲜的溢流形式流经北欧海洋。这种密集的北欧海溢流是全球海洋热量和淡水传送带的关键组成部分，被称为全球颠覆环流，有助于调节全球气候。因此，北极陆架水生产机制不仅对区域气候具有重要意义，而且对全球气候也具有重要意义。在这里提出的研究中，我的目标是描述北极大陆架上的混合过程，朝着全面了解北极地球-海洋系统迈出重要的第一步，并改进对未来变化及其对全球气候影响的预测。我感兴趣的具体问题是，如何利用潮汐能量来混合水团，无论是通过产生湍流，还是通过使垂直混合良好但横向不同的水柱变形并引起对流。我将讨论的另一个关键问题是，如何利用风能产生惯性振荡，这种振荡也可能与潮汐相互作用，导致混合。这些过程在温带陆架海已被证明是重要的，但尚未在北极大陆架经历的极端季节波动、大量河流淡水排放和结冰-融化-循环的环境中进行研究。我的策略是使用所有可用的数据来了解大陆架的海洋状态及其季节性的加热和冷却周期，然后绘制出大陆架上不同的混合制度，这样我们就可以确定如何、在哪里和何种类型的大陆架水被生产出来。然后，这些想法将被纳入陆架-海数字计算机模型，以测试陆架海系统对气候变化造成的河流流量和海冰损失增加的情景的敏感性。这将使我们能够诊断大陆架-海洋环流和气候系统的反馈，并帮助我们改进重要的大陆架过程在全球气候模型中的表现，并最终改善对我们未来气候的预测。

项目成果

Semidiurnal Tides on the Laptev Sea Shelf with Implications for Shear and Vertical Mixing

• DOI: 10.1175/jpo-d-12-0240.1
• 发表时间: 2014-01-01
• 期刊: JOURNAL OF PHYSICAL OCEANOGRAPHY
• 影响因子: 3.5
• 作者: Janout, Markus A.;Lenn, Yueng-Djern
• 通讯作者: Lenn, Yueng-Djern

Tide-induced vertical mixing in the Laptev Sea coastal polynya

• DOI: 10.1029/2011jc006966
• 发表时间: 2012-09
• 期刊: Journal of Geophysical Research
• 作者: I. Dmitrenko;S. Kirillov;E. Bloshkina;Y. Lenn

Shear at the Base of the Oceanic Mixed Layer Generated by Wind Shear Alignment

• DOI: 10.1175/jpo-d-12-0104.1
• 发表时间: 2013-08
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: L. Brannigan;Y. Lenn;T. Rippeth;E. McDonagh;T. Chereskin;J. Sprintall

Fate of Early 2000s Arctic Warm Water Pulse

• DOI: 10.1175/2010bams2921.1
• 发表时间: 2011-05
• 期刊: Bulletin of the American Meteorological Society
• 影响因子: 8
• 作者: I. Polyakov;Vladimir A Alexeev;I. Ashik;S. Bacon;A. Beszczynska-Möller;E. Carmack;I. Dmitrenko

Observed Atlantification of the Barents Sea Causes the Polar Front to Limit the Expansion of Winter Sea Ice

• DOI: 10.1175/jpo-d-18-0003.1
• 发表时间: 2018-08-01
• 期刊: JOURNAL OF PHYSICAL OCEANOGRAPHY
• 影响因子: 3.5
• 作者: Barton, Benjamin I.;Lenn, Yueng-Djern;Lique, Camille
• 通讯作者: Lique, Camille