The influence of Gulf Stream eddies and meanders on near-surface chlorophyll
The influence of Gulf Stream eddies and meanders on near-surface chlorophyll
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DOI：
10.1016/j.dsr.2017.02.006
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发表时间：
2017-04-01
影响因子：
2.4
通讯作者：
McGillicuddy, Dennis J., Jr.
中科院分区：
文献类型：
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作者：
Gaube, Peter;McGillicuddy, Dennis J., Jr.
墨西哥湾流区域包含强烈的中尺度变异性，这对那里的浮游生态系统产生了重大影响。在海平面异常图上，湾流的曲折可以被识别为向东传播的特征。这些曲流可能会变得不稳定，并被掐断，形成非线性的中尺度涡旋(环)，从而困住大片的水。在形成之后，被困在这些涡流中的生态系统在其一生中受到时间上变化的垂直速度的影响。由于水平平流和垂直通量，多种物理-生物机制可以同时影响被困在漩涡中的浮游植物群落。在这项研究中，我们通过比较卫星观测和涡旋分辨海洋模式来研究近地表叶绿素场(CHL)是如何在曲折和涡旋中演变的。在此之前的现场观测和卫星观测表明，在气旋性湾流曲折形成期间，CHL升高的水被向南输送。在反气旋蜿蜒中，CHL减少的水被向北输送。沿曲折前缘出现交替的亚中尺度上升流和下升流斑块；然而，在以曲折为中心的综合平均值中，没有观察到曲流诱导的垂直运动的生物反应的证据。在非线性墨西哥湾流涡的形成过程中，上升和抑制的环流分别在气旋和反气旋中被捕获并向西输送。在形成后，观察到CHL在反气旋的中心增加。在反气旋中观测到的CHL的正趋势与涡生Ekman抽吸(涡风相互作用)在反气旋中产生上升流和在气旋中产生下流的影响是一致的。为了证实涡致Ekman抽吸对墨西哥湾流涡中CHL的影响，我们比较了两个单独的涡旋分辨物理-生物模拟。第一个模拟是使用包含海洋表面流影响的真实表面应力强制进行的。第二个模拟忽略了这一过程。在这两个模拟中，涡旋内CHL的时间演化是非常不同的。包含涡流诱导的埃克曼泵浦的模型产生了与观测结果类似的CHL的时间趋势。
The Gulf Stream region contains strong mesoscale variability that significantly influences planktonic ecosystems residing therein. Meanders of the Gulf Stream can be identified as eastward propagating features in maps of sea level anomaly. These meanders can become unstable and pinch off to form nonlinear mesoscale eddies (rings) that trap large parcels of water. Following formation, ecosystems trapped within these eddies are subjected to temporally varying vertical velocities throughout their lifetime. As a result of both horizontal advection and vertical fluxes, multiple physical-biological mechanisms can simultaneously influence phytoplankton communities trapped in eddies. In this study we examine how the near-surface chlorophyll field (CHL) evolves in meanders and eddies by comparing satellite observations with an eddy-resolving ocean model.Prior in situ and satellite observations have revealed that during the formation of cyclonic Gulf Stream meanders, water with elevated CHL is transported southward. In anticyclonic meanders, water with reduced CHL is transported northward. Alternating submesoscale patches of upwelling and downwelling occur along the meandering front; however, evidence of a biological response to meander-induced vertical motion was not observed in meander-centric composite averages. During the formation of nonlinear Gulf Stream eddies, elevated and suppressed CHL is trapped and subsequently transported westward in cyclones and anticyclones, respectively. Following formation, CHL is observed to increase in the cores of anticyclones. The observed positive trend in CHL in anticyclones is consistent with the influence of eddy-induced Ekman pumping (eddy/wind interaction) that generates upwelling in anticyclones and downwelling in cyclones.To substantiate the influence of eddy-induced Ekman pumping on CHL in Gulf Stream eddies, two separate eddy-resolving physical-biological simulations are compared. The first simulation is forced with a realistic surface stress that includes the influence of ocean surface currents. The second simulation neglects this process. The time evolution of CHL within eddies is very different in these two simulations. The model that includes eddy-induced Ekman pumping generates temporal trends in CHL that are similar to the observations.