Abstract
In coastal and estuarine regions, ocean surface tracers like sea-surface temperature, chlorophyll-a, and sediments, form two frequently occurring patterns which can be explained by the influence of Lagrangian Coherent Structures (LCSs) on horizontal transport and mixing. In this study, we examined the role of two fundamental types of Coastally-Attached LCS configurations. The first configuration, referred to as Type-I, forms when an attracting or a repelling LCS is attached to the coastline at a single point. This configuration was found to enhance advective ocean tracer exchange between the coastal regions and the open ocean along its path. Moreover, it increases diffusive mixing by enhancing the interfacial area of tracer plumes, particularly those transported by rivers. Type-I structures generally emerge as a result of strong flow divergence and near-coast eddies. The second configuration, called Type-II, develops when an LCS is attached to the coastline at two points, forming an enclosed region in a near-heteroclinic manner. Unlike the Type-I configuration, Type-II inhibits advective mixing between coastal and open-ocean waters. The Type-II configuration arises due to flow separation from the coastline at one point and its subsequent reattachment downstream, leading to recirculation in the enclosed region. Both configurations are capable of generating strong gradients in surface tracer fields, potentially leading to frontal systems if they persist for extended periods. These findings would potentially contribute to enhanced understanding of the complex dynamics of coastal tracer distribution and their implications on nearshore circulation, ecology, and pollutant transport.