This study explores the impact of sub-mesoscale structures and vertical advection on the connectivity properties of the Baltic Sea using a Lagrangian approach. High-resolution flow fields from the General Estuarine Transport Model (GETM) were employed to compute Lagrangian trajectories, focusing on the influence of fine-scale structures on connectivity estimates. Six river mouths in the Baltic Sea served as initial positions for numerical particles, and trajectories were generated using flow fields with varying horizontal resolutions: 3D trajectories with 250m resolution as well as 2D trajectories with 250m and 1km resolutions. Several Lagrangian indices, such as mean transit time, arrival depths, and probability density functions of transit times, were analyzed to unravel the complex circulation of the Baltic Sea and highlight the substantial impact of sub-mesoscale structures on numerical trajectories. Results indicate that in 2D simulations, particles exhibit faster movement on the eastern side of the Gotland Basin in high-resolution compared to coarse-resolution simulations. This difference is attributed to the stronger coastal current in high-resolution compared to coarse-resolution simulations. Additionally, the study investigates the influence of vertical advection on numerical particle motion within the Baltic Sea, considering the difference between 3D and 2D trajectories. Findings reveal that denser water in the eastern and south-eastern areas significantly affects particle dispersion in 3D simulations, resulting in increased transit times. Conversely, regions in the North-western part of the basin accelerate particle movement in 3D compared to the 2D simulations. Finally, we calculated the average residence time of numerical particles exiting the Baltic Sea through the Danish strait. Results show an average surface layer residence time of approximately 790 days over an eight-year integration period, highlighting the relatively slow water circulation in the semi-enclosed Baltic Sea basin. This prolonged residence time emphasizes the potential for the accumulation of pollutants. Overall, the study underscores the pivotal role of fine-scale structures in shaping the connectivity of the Baltic Sea, with implications for understanding and managing environmental challenges in this unique marine ecosystem.

中文翻译：

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通过拉格朗日分析研究亚中尺度海流结构对波罗的海连通性的影响

本研究采用拉格朗日方法探讨了亚中尺度结构和垂直平流对波罗的海连通性的影响。采用通用河口输运模型 (GETM) 的高分辨率流场来计算拉格朗日轨迹，重点关注精细尺度结构对连通性估计的影响。波罗的海的六个河口作为数值粒子的初始位置，使用不同水平分辨率的流场生成轨迹：分辨率为 250m 的 3D 轨迹以及分辨率为 250m 和 1km 的 2D 轨迹。分析了平均渡越时间、到达深度和渡越时间概率密度函数等几个拉格朗日指数，以揭示波罗的海的复杂环流，并强调亚介尺度结构对数值轨迹的重大影响。结果表明，在二维模拟中，与粗分辨率模拟相比，在高分辨率下，颗粒在哥特兰盆地东侧表现出更快的运动。这种差异归因于与粗分辨率模拟相比，高分辨率的沿海流更强。此外，考虑到 3D 和 2D 轨迹之间的差异，该研究还研究了垂直平流对波罗的海内数值粒子运动的影响。研究结果表明，东部和东南部地区的水密度较大，会显着影响 3D 模拟中的颗粒分散，导致传输时间增加。相反，与 2D 模拟相比，盆地西北地区的 3D 颗粒运动加速。最后，我们计算了通过丹麦海峡离开波罗的海的数值粒子的平均停留时间。结果显示，在八年的整合期内，表层平均停留时间约为 790 天，凸显了半封闭的波罗的海盆地相对缓慢的水循环。这种延长的停留时间强调了污染物积累的可能性。总体而言，该研究强调了精细结构在塑造波罗的海连通性方面的关键作用，对于理解和管理这一独特海洋生态系统中的环境挑战具有重要意义。