Understanding transport and mixing properties in turbulent flows is a challenging problem not only from the theoretical point of view but also for more applied issues, such as oil spill management, SAR operations, plankton distribution and ecological connectivity. Owing to its inherent turbulent nature, ocean dynamics is highly complex, which makes the assessment of water pathways and the study of oceanic transport phenomena an extraordinarily complicated task. This problem can be approached from a Lagrangian perspective that studies transport and mixing by following trajectories of fluid particles. While the Eulerian perspective describes the basic characteristics of a velocity field, the Lagrangian one addresses its effects on transported substances, which clearly is of utmost relevance for coastal management including marine safety and marine ecosystems protection and management. Lagrangian analysis of the ocean flow based on dynamical systems and complex network theory has been used to develop new approaches to characterize the oceanic flow. They have led to the identification of coherent transport flow structures (i.e. filaments, eddies, fronts, flow avenues, etc) and connectivity patterns, with large proven impacts on biogeochemical cycling and population dynamics. Lagrangian approaches allow indeed to effectively track coupled bio- physical processes occurring along the history of moving fluid parcels. This session invites contributions dealing with Lagrangian approaches aiming at assessment of ocean dynamics and studying the interplay between physical and biological processes (i.e. from biogeochemical tracers to higher trophic levels). Priority will be given to studies that encompass the theoretical point of view, multi-platform ocean observations (drifters, HF radar, satellite data, etc…), numerical modeling and laboratory experiments. The objective of this session is to discuss and stress the importance of properly characterizing Lagrangian transport and connectivity at different scales to best appraise their highly nonlinear impacts on marine organisms, in the context of global changes. The interdisciplinary character of biological, biogeochemical and physical interactions of this session encourages an exchange of ideas and contributions across different fields, such as physical and biological oceanography, complex systems, marine ecology, geophysical fluid dynamics and applied mathematics.
Lead Organizer: Alejandro Orfila, Spanish National research Council - CSIC (alejandro.orfila@csic.es)
Co-organizers:
Ismael Hernández-Carrasco, IMEDEA-UIB (ihernandez@imedea.uib-csic.es)
Vincent Rossi, MIO-CNRS (vincent.rossi@mio.osupytheas.fr)
Cristobal López, IFISC-UIB (clopez@ifisc.uib-csic.es)
Annalissa Bracco, Georgia Institute of Technology, School of Earth and Atmospheric Sciences (abracco@gatech.edu)
Presentations
10:30 AM
LAgrangian transport of MARIne litter from modeling, analysis, and observations in CoAstal waters of the Bay of Biscay (5628)
Primary Presenter: Anna Rubio, AZTI (arubio@azti.es)
Marine litter constitutes an environmental threat of growing concern around world oceans. Its spatial distribution is governed by different physical processes (including wind, waves and currents) characterized by a wide range of variability and complex interactions that result in aggregation and scatter of marine litter. In this context, LAgrangian transport of MARine litter and microplastics from modelling, analysis, and observations in CoAstal waters (LAMARCA) project aims to further understand the role of oceanic turbulence in marine litter (microplastics and meso/macrolitter) coastal aggregations, with special emphasis on scales from 1 m to 10 km, where the vertical motions play a relevant role. This project, which started in 2022, proposes an approach that combines ocean-current structures, oceanographic surveys, and new Lagrangian tools from complex systems to characterize marine connectivity and mixing properties in coastal waters. In April and October 2022, two 3-day multiplatform experiments were performed in the SE Bay of Biscay to study the aggregation of surface litter along frontal processes by means of the deployment of several clusters of surface drifters, high resolution transects with a towed ADCP, measurements of surface currents with an HF-radar, numerical simulations, and visual observations. We discuss preliminary results of dispersion properties and flow structure characterization obtained from different Lagrangian analysis diagnostics, including finite-size Lyapunov exponents and Lagrangian averaged divergence.
10:45 AM
Spatial coalescent connectivity through multi-generation dispersal modelling predicts gene flow across marine phyla (6337)
Primary Presenter: Vincent Rossi, CNRS (vincent.rossi.ocean@gmail.com)
Gene flow governs the contemporary spatial structure and dynamic of populations as well as their long-term evolution. For species dispersing through atmospheric or oceanic flows, biophysical models allow predicting the migratory component of gene flow, which facilitates the interpretation of broad-scale structure inferred from allele frequencies among populations. However, frequent mismatches between dispersal estimates and observed genetic diversity prevent an operational synthesis for eco-evolutionary projections. Here we use an extensive compilation of 58 population genetic studies of 47 phylogenetically divergent marine sedentary species over the Mediterranean basin to assess how genetic differentiation is predicted by Isolation-By-Distance, single-generation and multigenerational dispersal models. The latter estimate random-walk connectivity probabilities across any numbers of steps in a generic temporal, directed, and weighted network characterizing ocean transport. They unveil explicit parents-to-offspring links (filial or explicit connectivity, realized by causal paths) and links among siblings from a common ancestor (coalescent or implicit connectivity, related to pitchfork motifs). We find that almost 70 % of observed variance in genetic differentiation is explained by coalescent connectivity over multiple generations, significantly outperforming other models. Our results bring novel insights into how ocean currents drive seascape connectivity and allow untangling the forces that shape population structure as well as anticipating climate-driven redistributions.
11:00 AM
CONNECTIVITY BOTTLENECKS IN OCEAN FLOWS CHARACTERIZED BY THE LAGRANGIAN BETWEENNESS (6397)
Primary Presenter: Emilio Hernandez-Garcia, IFISC (CSIC-UIB) (emilio@ifisc.uib-csic.es)
Several quantities computed by Lagrangian methods are being used to qualify local properties of ocean flow at different locations: rotation, stretching, convergence or divergence, shear, presence of flow barriers, etc., providing useful tools to characterize transport. Going beyond local characterization, ocean connectivity properties have also been addressed with Lagrangian methods, for example by using Lagrangian flow networks. The presence of ‘bottlenecks’ or congestion areas (i.e. regions that should be crossed by water traveling between many distant origins and destinations) is conveniently identified by network-based measures such as the betweenness centrality. Here we combine the connectivity ideas with local transport properties to define a ‘Lagrangian betweenness’ [1], able to identify and to quantify the presence of bottlenecks in regions of the flow. We illustrate the use and meaning of the Lagrangian betweenness by identifying bottlenecks in ocean surface flows in the Adriatic Sea and in the Kerguelen region in the Southern Ocean. Also, by analyzing plankton abundance data from the Kuroshio region in the Pacific Ocean, we find significant spatial correlations between measures of biological diversity and betweenness, suggesting that ocean bottlenecks act as ecological hot spots. [1] E. Ser-Giacomi, A. Baudena, V. Rossi, M. Follows, S. Clayton, R. Vasile, C. Lopez, E. Hernandez-Garcia (2021), Lagrangian betweenness as a measure of bottlenecks in dynamical systems with oceanographic examples, Nature Communications 12, 4935.
11:15 AM
Convergence and vertical velocities at the sea surface from Lagrangian trajectories (6595)
Primary Presenter: Daniel Tarry, IMEDEA (CSIC-UIB) (drtarry@imedea.uib-csic.es)
Vertical velocities are difficult to measure directly and their prediction is challenging. Identifying the 3D pathways that connect the surface ocean to the interior is one of the goals of the DRI CALYPSO project. These pathways are pivotal for predicting the distribution of pollutants, oxygen, heat, carbon, and other biogeochemical tracers. Recent studies have shown that vertical transport is influenced by flows at many scales and demonstrate that vertical motions associated with horizontal scales smaller than 10 km play a significant role in vertical exchanges. Lagrangian instruments can cover large distances on their own, thereby reducing the need for (costly and slow) direct sampling. Due to the time-evolving nature of the flow, a Lagrangian approach is favored to study the transport and dispersion of water properties. Studying frontogenesis and subduction in the Lagrangian frame is more advantageous than in the Eulerian frame. Cluster experiments give information about the two-dimensional structure of the flow field, and the relative deformation of swarms of drifters by the velocity at multiple spatial scales. Here we use Lagrangian trajectories from drifter observations deployed during the CALYPSO 2022 cruise on a coherent submesoscale cyclonic eddy which was sampled for 14 days. During that time several episodes of surface convergence and downwelling were observed and analyzed. The results show convergences of order -1f and reveal downwelling velocities of -60 m/day.
11:30 AM
Mapping frontal systems with surface Lagrangian drifters in the North Sea (7092)
Primary Presenter: Thomas Badewien, University of Oldenburg (thomas.badewien@uni-oldenburg.de)
Lagrangian approaches enable to study circulation patterns in coastal oceans in great spatial and temporal detail. Here, we present a large data set on circulation patterns in the North Sea with a focus on the frontal systems in the Skagerrak – the transition area between the Baltic and North Sea. The data set encompasses measurements obtained from Lagrangian surface drifters which were deployed during several cruises between 2017 to 2021. Our research group at the ICBM (University of Oldenburg) designed the low-cost drifters for studying coastal dynamics and exchange processes in tidal systems. We also used clusters of drifters to analyze in detail fine sub-mesoscale fluid dynamics, such as divergence and eddy dynamics. Based on the large data set, we provide high-resolution surface current maps and show representations of tidal dynamics in the North Sea. Our data reveal significant differences between the mostly shallow areas of the North Sea and the deep Skagerrak. While tidal currents dominate the shallow coastal areas, deep areas are characterized by a high mean residual circulation driven by high density gradients. The data sets are well suited for model validation and further studies on sea surface dynamics in frontal zones including mixing processes. The detailed knowledge of surface currents obtained by the measurements also help study the impact of hydrodynamics on processes at the sea-air-interface.
11:45 AM
Lagrangian transport as potential transport routes of fish larvae off the National Park of Cabo Pulmo at the entrance of the Gulf of California, Mexico (October, 2022) (7382)
Primary Presenter: Leonardo Tenorio-Fernandez, CICIMAR (leonardo.tenof@gmail.com)
Lagrangian transport as potential transport routes of fish larvae off the National Park of Cabo Pulmo at the entrance of the Gulf of California were analyzed. CTD and zooplankton samples were collected in transects off Cabo Pulmo and oceanic adjacent areas during October, 2022. Preliminary results from satellite and in situ data showed an anticyclonic eddy in front of Cabo Pulmo. A Lagrangian particle tracking model applied at the sampling stations, where the fish larvae were collected, showed that the particles sown in the sampling stations affected by the eddy circulation were trapped by this structure, and the sampling stations closer to the coast were displaced to north trapped in a coast poleward current. It is possible that the mesoscale activity reported off Cabo Pulmo support the recruitment of most fish species close to the spawning areas.
SS095B Lagrangian Transport and Connectivity in Oceanic Flows: Applications to Ocean Dynamics and Marine Ecosystems.
Description
Time: 10:30 AM
Date: 5/6/2023
Room: Sala Ibiza B