Jonathan Rogerson , Jennifer Veitch , Samantha Siedlecki , Sarah Fawcett
{"title":"Frontal features and mixing regimes along the shelf region of the Southern Benguela upwelling system","authors":"Jonathan Rogerson , Jennifer Veitch , Samantha Siedlecki , Sarah Fawcett","doi":"10.1016/j.csr.2025.105560","DOIUrl":null,"url":null,"abstract":"<div><div>Mesoscale fronts are ubiquitous features in all Eastern Boundary Upwelling Systems and are the result of prominent sea surface temperature (SST) gradients and baroclinic jets. Their seasonal variability and presence can impact the horizontal mixing patterns of particles and nutrients. Here, we examine the role of alongshore fronts in shaping the seasonal patterns of cross-shore mixing, residence times, and surface particle transport along the shelf region of the Southern Benguela Upwelling System. Using a numerical ocean model together with a front-detection algorithm, Lagrangian particle tracking, and Finite Time Lyapunov Exponents, we investigate mesoscale frontal variability. In summer, fronts are typically long and continuous alongshore features that are defined by strong SST gradients and associated with prominent Lagrangian Coherent Structures (LCSs). These fronts can act as cohesive barriers that limit cross-shore mixing and offshore advection of particles. In winter, fronts are generally found further offshore and are more filamentous and numerous compared to summer. Furthermore, they are defined by weaker SST frontal gradients and shorter frontal lengths. Fronts in winter are not associated with any obvious LCSs, which implies that particles and material experience greater rates of dispersion and cross-shore mixing. Lagrangian float experiments confirm this and show surface particle trajectories in winter to be more variable and chaotic compared to the more uniform patterns observed in summer. Therefore, defined alongshore fronts in summer aid in the retention of particles on the shelf. The seasonal erosion of these defined frontal features allows for greater cross-shore mixing of particles, water masses and nutrients in the upper water column during winter.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105560"},"PeriodicalIF":2.2000,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Continental Shelf Research","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0278434325001608","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"OCEANOGRAPHY","Score":null,"Total":0}
引用次数: 0
Abstract
Mesoscale fronts are ubiquitous features in all Eastern Boundary Upwelling Systems and are the result of prominent sea surface temperature (SST) gradients and baroclinic jets. Their seasonal variability and presence can impact the horizontal mixing patterns of particles and nutrients. Here, we examine the role of alongshore fronts in shaping the seasonal patterns of cross-shore mixing, residence times, and surface particle transport along the shelf region of the Southern Benguela Upwelling System. Using a numerical ocean model together with a front-detection algorithm, Lagrangian particle tracking, and Finite Time Lyapunov Exponents, we investigate mesoscale frontal variability. In summer, fronts are typically long and continuous alongshore features that are defined by strong SST gradients and associated with prominent Lagrangian Coherent Structures (LCSs). These fronts can act as cohesive barriers that limit cross-shore mixing and offshore advection of particles. In winter, fronts are generally found further offshore and are more filamentous and numerous compared to summer. Furthermore, they are defined by weaker SST frontal gradients and shorter frontal lengths. Fronts in winter are not associated with any obvious LCSs, which implies that particles and material experience greater rates of dispersion and cross-shore mixing. Lagrangian float experiments confirm this and show surface particle trajectories in winter to be more variable and chaotic compared to the more uniform patterns observed in summer. Therefore, defined alongshore fronts in summer aid in the retention of particles on the shelf. The seasonal erosion of these defined frontal features allows for greater cross-shore mixing of particles, water masses and nutrients in the upper water column during winter.
期刊介绍:
Continental Shelf Research publishes articles dealing with the biological, chemical, geological and physical oceanography of the shallow marine environment, from coastal and estuarine waters out to the shelf break. The continental shelf is a critical environment within the land-ocean continuum, and many processes, functions and problems in the continental shelf are driven by terrestrial inputs transported through the rivers and estuaries to the coastal and continental shelf areas. Manuscripts that deal with these topics must make a clear link to the continental shelf. Examples of research areas include:
Physical sedimentology and geomorphology
Geochemistry of the coastal ocean (inorganic and organic)
Marine environment and anthropogenic effects
Interaction of physical dynamics with natural and manmade shoreline features
Benthic, phytoplankton and zooplankton ecology
Coastal water and sediment quality, and ecosystem health
Benthic-pelagic coupling (physical and biogeochemical)
Interactions between physical dynamics (waves, currents, mixing, etc.) and biogeochemical cycles
Estuarine, coastal and shelf sea modelling and process studies.