Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre from Sustained Glider Observations
Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre from Sustained Glider Observations
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DOI：
10.1029/2018jc014162
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发表时间：
2018-08
影响因子：
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通讯作者：
L. Houpert;M. Inall;E. Dumont;S. Gary;C. Johnson;M. Porter;W. Johns;S. Cunningham
中科院分区：
文献类型：
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作者：
L. Houpert;M. Inall;E. Dumont;S. Gary;C. Johnson;M. Porter;W. Johns;S. Cunningham
2014-2016年期间获得的重复滑翔机剖面，作为副极地北大西洋计划翻转的一部分，用于量化罗卡尔高原上空北大西洋洋流（NAC）分支的环流和运输。利用沿着58 ° N、21 ° W ~ 15 ° W收集的16个滑翔剖面，计算了绝对地转速度，进而描述了输送的水平和垂直结构。罗卡尔高原向北的年平均输送量（±标准差）为5.1 ± 3.2 Sv。夏季（5 ~ 10月）平均向北输送较强，达6.7 ± 2.6Sv。这占Sarafanov等人（2012年，https：//doi.org/10.1029/2011JC 007572）估计的沿沿着59.5 N、雷克雅内斯海脊和苏格兰之间的上层海洋沃茨（σO < 27.55 kg/m 3）NAC总输送量的43%。确定了NAC的两个准永久性向北流动分支：（i）位于冰岛海盆东侧（20.5 W至18.5 W）的哈顿浅滩急流（6.3 ± 2.1 Sv）和（ii）位于哈顿-罗科尔海盆东侧（16 W至15 W）的罗科尔浅滩急流（1.5 ± 0.7 Sv）。在夏季，与罗卡尔岸急流有关的输送大多与深度无关，而哈顿岸急流输送的30%是由于垂直地转切变。使用蒙特卡罗方法估计每个单独的滑翔机部分的不确定性，绝对运输的平均不确定性小于0.5 Sv。虽然与基于测高的估计比较表明类似的大尺度环流模式，测高数据不解决小的中尺度电流带在哈顿-罗科尔盆地，这是非常需要正确的运输估计。越来越多的证据表明，北大西洋洋流（墨西哥湾流的东延部分）输送的热量和淡水严重影响着欧洲和全球的气候。为了充分测量这股水流并了解其动力学，水下滑翔机航行在罗卡尔高原，这是北大西洋的一个偏远地区，距离苏格兰400多公里。这些机器人可以在海洋表面下一公里处收集数据，由于它们的低能耗，可以一次运行数千公里，持续数月。这项研究分析了2年来在北大西洋连续海洋滑翔机测量，揭示了两个分支的北大西洋电流在罗卡尔高原，我们命名为哈顿银行喷气机和罗卡尔银行喷气机。第一次，这些电流的每月变化的特点（速度和水平/垂直延伸）。这些分支携带了北大西洋海流输送的上层海洋沃茨的很大一部分（40%）。这项工作突出了使用自主水下航行器作为海洋观测站一部分的重要性。除了监测北大西洋的状况外，这些水下机器人还帮助我们了解其动态，这对欧洲和全球气候产生了影响。
Repeat glider sections obtained during 2014–2016, as part of the Overturning in the Subpolar North Atlantic Program, are used to quantify the circulation and transport of North Atlantic Current (NAC) branches over the Rockall Plateau. Using 16 glider sections collected along 58∘N and between 21∘W and 15∘W, absolute geostrophic velocities are calculated, and subsequently the horizontal and vertical structure of the transport are characterized. The annual mean northward transport (± standard deviation) is 5.1 ± 3.2 Sv over the Rockall Plateau. During summer (May to October), the mean northward transport is stronger and reaches 6.7 ± 2.6 Sv. This accounts for 43% of the total NAC transport of upper-ocean waters (σO < 27.55 kg/m 3) estimated by Sarafanov et al. (2012, https://doi.org/10.1029/2011JC007572) along 59.5∘N, between the Reykjanes Ridge and Scotland. Two quasi-permanent northward flowing branches of the NAC are identified: (i) the Hatton Bank Jet (6.3 ± 2.1 Sv) over the eastern flank of the Iceland Basin (20.5∘W to 18.5∘W) and (ii) the Rockall Bank Jet (1.5 ± 0.7 Sv) over the eastern flank of the Hatton-Rockall Basin (16∘W to 15∘W). Transport associated with the Rockall Bank Jet is mostly depth independent during summer, while 30% of the Hatton Bank Jet transport is due to vertical geostrophic shear. Uncertainties are estimated for each individual glider section using a Monte Carlo approach, and mean uncertainties of the absolute transport are less than 0.5 Sv. Although comparisons with altimetry-based estimates indicate similar large-scale circulation patterns, altimetry data do not resolve small mesoscale current bands in the Hatton-Rockall Basin which are strongly needed for the right transport estimates. Plain Language Summary There is mounting evidence that heat and freshwater transported by the North Atlantic Current (eastward extension of the Gulf Stream) heavily influences European and global climate. To adequately measure this current and understand its dynamics, underwater gliders navigate over the Rockall Plateau, a remote region of the North Atlantic located more than 400 km off Scotland. These robots collect data up to a kilometer beneath the ocean’s surface and, due to their low energy consumption, can operate over thousands of kilometers for months at a time. This study analyzes 2 years of continuous ocean glider measurements in the North Atlantic and reveals two branches of the North Atlantic Current over the Rockall Plateau that we named the Hatton Bank Jet and the Rockall Bank Jet. For the first time, the monthly variability of these currents was characterized (speed and horizontal/vertical extension). These branches carry a significant portion of the upper-ocean waters transported by the North Atlantic Current (40%). This work highlights the importance of using autonomous underwater vehicles as part of an ocean observatory. In addition to monitoring the state of the North Atlantic Ocean, these underwater robots help us understand its dynamics, which impacts the European and global climate.