Abstract Influence of frontal dynamics on phytoplankton distribution and composition was studied combining in situ observations and Lagrangian computations from altimetry satellite derived currents. Four transects during the SHEBEX cruise (May 2015) over the Western Mediterranean were examined identifying a region with high spatial variability in the dynamical and biogeochemical properties. The dynamical situation unraveled from the Lagrangian analysis is dominated by filaments originated by an anticyclonic–cyclonic eddy interaction that organize the transport, modifying the biogeochemical properties of the water column and shaping the satellite derived surface Chlorophyll a (chla) distribution. The properties of the water column have been analyzed in relation to the dynamical properties of the filaments showing that local variation of the mixed layer and nutricline depths are correlated with the spatial variability of finite size Lyapunov exponents. Furthermore, the composition of phytoplankton community was studied regarding the path-accumulated properties of the flow during the formation of the filaments. In this regard new metrics accounting the Lagrangian evolution of the turbulent and topological properties of the flow along fluid parcel trajectories have been developed. Here we provide observational evidence that fluid parcels associated with high Lagrangian turbulent kinetic energy and Lagrangian positive vorticity host higher presence of larger pennate diatoms (i.e. Pseudo-nitzschia spp). Our findings indicate that the combination of these diagnostics provides an improved description of the turbulent dynamics showing that the Lagrangian properties of the flow have important biological consequences for phytoplankton to high ecological levels.

中文翻译：

---

拉格朗日流对沿着丝状结构的浮游植物丰度和组成的影响

摘要 结合原位观测和测高卫星导出电流的拉格朗日计算，研究了锋面动力学对浮游植物分布和组成的影响。对 SHEBEX 巡航（2015 年 5 月）西地中海期间的四个横断面进行了检查，确定了一个在动力和生物地球化学特性方面具有高度空间变异性的区域。拉格朗日分析揭示的动力学情况主要由反气旋-气旋涡旋相互作用产生的细丝主导，这些细丝组织运输、改变水柱的生物地球化学特性并塑造卫星衍生的表面叶绿素 a (chla) 分布。已经分析了与细丝的动力学特性相关的水柱特性，表明混合层和营养线深度的局部变化与有限大小的 Lyapunov 指数的空间变化相关。此外，还研究了浮游植物群落的组成，涉及细丝形成过程中流动的路径累积特性。在这方面，已经开发了考虑沿流体包裹轨迹的流动的湍流和拓扑特性的拉格朗日演化的新度量。在这里，我们提供了观察证据，表明与高拉格朗日湍流动能和拉格朗日正涡度相关的流体包裹体中存在较大的羽状硅藻（即 Pseudo-nitzschia spp）。