| GUO Guijun,SHI Jiuxin,JIAO Yutian. 2016. Turbulent mixing in the upper ocean of the northwestern Weddell Sea, Antarctica. Acta Oceanologica Sinica, 35(3):1－9 |
| Turbulent mixing in the upper ocean of the northwestern Weddell Sea, Antarctica |
| 南极西北威德尔海上层海洋湍流混合研究 |
| Received:September 10, 2015 Revised:November 09, 2015 |
| DOI：10.1007/s13131-016-0816-y |
| Key words:mixing dissipation rate turbulent diffusivity upper ocean Weddell Sea |
| 中文关键词: 混合 湍动能耗散率 湍扩散率 上层海洋 威德尔海 |
| 基金项目: |
| Author Name | Affiliation | E-mail | | GUO Guijun | Key Laboratory of Physical Oceanography, Ocean University of China, Qingdao 266003, China
College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China | | | SHI Jiuxin | Key Laboratory of Physical Oceanography, Ocean University of China, Qingdao 266003, China
College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China | shijiuxin@ouc.edu.cn | | JIAO Yutian | Key Laboratory of Physical Oceanography, Ocean University of China, Qingdao 266003, China | |
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| Abstract: |
| Turbulent mixing in the upper ocean (30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature, salinity and microstructure data obtained during February 2014. Vertical thermohaline structures are distinct due to geographic features and sea ice distribution, resulting in that turbulent dissipation rates (ε) and turbulent diffusivity (K) are vertically and spatially non-uniform. On the shelf north of Antarctic Peninsula and Philip Ridge, with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m, both ε and K show significantly enhanced values in the order of O(10-7)-O(10-6) W/kg and O(10-3)-O(10-2) m2/s respectively, about two or three orders of magnitude higher than those in the open ocean. Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau, where ε decreases with depth from O(10-8) to O(10-9) W/kg, while K changes vertically in an inverse direction relative to ε from O(10-6) to O(10-5) m2/s. In the marginal ice zone, K is vertically stable with the order of 10-4 m2/s although both intense dissipation and strong stratification occur at depth of 50-100 m below a cold freshened mixed layer. Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions, our results indicate weak relationship between K and wind stress or tidal kinetic energy. Instead, intensified mixing occurs with large bottom roughness, demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing. In addition, geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing. |
| 中文摘要: |
| 利用中国第30次南极考察期间于2014年2月在西北威德尔海获得的温度、盐度剖面数据和湍流数据,本文对该海域上层海洋(30-200 m)混合过程进行了研究。受地形特征和海冰分布影响,观测海域垂向热盐结构存在着明显的不同,使得湍动能耗散率(ε)和湍扩散率(K)在垂向和空间上都存在着显著的差异。在南极半岛北侧陆架和菲利普海岭处,上层200 m温度和盐度剖面垂向上相对均匀,ε和K在此显著高于其他区域,分别达到O(10-7)-O(10-6) W·kg-1和O(10-3)-O(10-2) m2·s-1量级,比开阔大洋要高两到三个量级。在鲍威尔海盆和南奥克尼海台,受上层海洋强层化遏制,该区域上层海洋混合水平与开阔大洋水平相当。在此,ε随着深度加深从O(10-8)降到O(10-9) W·kg-1,而K受密度跃层内强层化制约呈现出与ε相反的垂向变化趋势,随深度从O(10-6)增长到O(10-5) m2·s-1。在海冰外缘区,虽然耗散水平在50-100 m出现了较高水平,但是密度跃层内层化的加强弱于无冰区威德尔海海域,因此K在垂向上保持相对稳定,维持在10-4 m2·s-1量级。目前的研究将风和潮汐作为近岸海域海洋混合的主要能量来源,但我们的结果显示湍扩散率K与风应力和潮汐动能关系并不显著。混合强烈的海域一般都伴有海底粗糙度高值的出现,表明风和潮汐产生的内波只有在撞击到陡峭地形时才能耗散到湍流尺度激发混合的发生。另外威德尔海水通过菲利普通道西侧的缺口流出威德尔海,这也是造成此处产生强混合的一个能量来源。 |
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