A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications
A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications
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DOI：
10.1002/2016jc012634
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发表时间：
2017-08-01
影响因子：
3.6
通讯作者：
Raimbault, Patrick
中科院分区：
文献类型：
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作者：
Bosse, Anthony;Testor, Pierre;Raimbault, Patrick
2013年6月，一架装有氧气和荧光传感器的滑翔机在利古里亚海（地中海西北部）对一个反气旋亚中尺度相干涡（SCV）进行了广泛采样。这些测量由全深度CTD铸型（T、S和氧）和水样进行补充，记录SCV内外的营养物质和浮游植物色素。在4.5个月前的冬季深层对流事件中，在300 - 1200米之间形成了一个非常均匀的含氧水核心。它具有强烈的动力特征，在700 m深度处具有13.9 cm s（-1）的旋转地转平衡峰值速度。涡旋半径较小，为6.2 km，对应高罗斯比数-0.45。涡中心涡度达到-0.8f。由于与扩散系数约为0.2 m(2) s（-1）相关的SCV设置的动力障碍，发现示踪剂在涡旋核和周围环境之间的横流等流扩散非常有限。岩心深处的硝酸盐、磷酸盐和硅酸盐的浓度比周围丰富的水域低13-18%，营养物质匮乏。然而，营养线向海面移动了约20-50米，从而增加了浮游植物的营养可利用性。叶绿素最大值处的叶绿素-a浓度随后约为室外的两倍。色素进一步揭示了涡旋内纳米浮游植物的优势和初级生产力的增强。该研究揭示了对流后scv对营养物分布和浮游植物群落，以及随后的初级生产和碳固存的重要影响。由于冬季恶劣的气象条件，世界海洋的一些地方经历了地表水的强烈冷却，并在一个称为海洋深层对流的过程中开始下沉。它对海洋的功能至关重要，而且对海洋生物学也至关重要，因为它将氧气带到表层以下，将营养物质带到表层，从而刺激浮游植物的生长。在这项研究中，我们以前所未有的细节描述了2013年冬季在地中海西北部法国南部发生的对流事件后形成的涡流的物理学及其生物学意义。这个海洋涡旋的半径约为6公里，在750米左右的地方有一个地下特征，旋转速度约为15厘米/秒。对于海洋涡旋来说，它的大小相当小，这使得它的采样和探测特别具有挑战性。这种类型的漩涡能够在安静的深海中存活数年，这个标本是在它形成4.5个月后观察到的。一艘船在涡流内收集的水样使我们第一次能够进一步评估它对营养物质浓度的影响，以及对浮游植物大小群的影响。
In June 2013, a glider equipped with oxygen and fluorescence sensors has been used to extensively sample an anticyclonic Submesoscale Coherent Vortex (SCV) in the Ligurian Sea (NW Mediterranean Sea). Those measurements are complemented by full-depth CTD casts (T, S, and oxygen) and water samples documenting nutrients and phytoplankton pigments within the SCV and outside. The SCV has a very homogeneous core of oxygenated waters between 300 and 1200 m formed 4.5 months earlier during the winter deep convection event. It has a strong dynamical signature with peak velocities at 700 m depth of 13.9 cm s(-1) in cyclogeostrophic balance. The eddy has a small radius of 6.2 km corresponding to high Rossby number of -0.45. The vorticity at the eddy center reaches -0.8f. Cross-stream isopycnic diffusion of tracers between the eddy core and the surroundings is found to be very limited due to dynamical barriers set by the SCV associated with a diffusivity coefficient of about 0.2 m(2) s(-1). The deep core is nutrients-depleted with concentrations of nitrate, phosphate, and silicate, 13-18% lower than the rich surrounding waters. However, the nutriclines are shifted of about 20-50 m toward the surface thus increasing the nutrients availability for phytoplankton. Chlorophyll-a concentrations at the deep chlorophyll maximum are subsequently about twice bigger as compared to outside. Pigments further reveal the predominance of nanophytoplankton inside the eddy and an enhancement of the primary productivity. This study demonstrates the important impact of postconvective SCVs on nutrients distribution and phytoplankton community, as well as on the subsequent primary production and carbon sequestration.Plain Language Summary Due to harsh meteorological conditions in winter, a few places of the world's ocean experience an intense cooling of their surface waters that start to sink in a process called oceanic deep convection. It is crucial for the functioning of the ocean, but also the marine biology as it brings oxygen deep below the surface and nutrients up to the surface thereby stimulating phytoplankton growth. In this study, we describe with unprecedented details the physics and its biological implications of an eddy formed after a convective event occurring in winter 2013 south of France in the northwestern Mediterranean Sea. This oceanic eddy has a radius of about 6 km and a subsurface signature with intensified rotation of about 15 cm/s at around 750 m. Its size is rather small for an oceanic eddy and makes it particularly challenging to sample and detect. This type of eddies are able to live for years in the quiescent deep ocean and this specimen was observed 4.5 months after its formation. Water samples collected by a ship inside the eddy enable us to further evaluate for the first time its influence on the nutrients concentration, as well as on the phytoplankton size group.