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)
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
08:30 AM
Lagrangian features as predictors of marine predators’ distribution (4681)
Primary Presenter: Jerome Pinti, University of Delaware (pintijerome@gmail.com)
Most studies of pelagic predator distributions have focused on ocean conditions coincident in time and space with the animal (Eulerian, or state predictors), without consideration of the dynamic history of the water parcel selected by the predator (Lagrangian predictors). However, there is growing evidence that some marine organisms (including elephant seals, frigatebirds, penguins) may select for Lagrangian and not just Eulerian features. Lagrangian predictors can capture filaments, eddies, and fronts as well as along-trajectory processes such as accumulation of biomass that cannot easily be extracted from Eulerian fields. These features have the potential to reveal preferred habitats for marine species. This is important, as it will strengthen our capacity to predict where marine predators are, thus enabling to design more precise and dynamic conservation and fisheries management plans. Here, we present a method that tests for the selection for Lagrangian features in marine predators. We use HYCOM, a global data-constrained ocean circulation model to compute two different Lagrangian predictors, Finite-Time Lypanuov Exponent (FTLE) and dilation rate. We then couple these predictors with the TOPP (Tracking of Pacific Predators) dataset to assess the selection of Lagrangian features by 42 different species of marine predators, ranging from sea turtles to sharks, elephant seals, and whales.
08:45 AM
USING LAGRANGIAN COHERENT STRUCTURES TO QUANTIFY PREY CONCENTRATING FEATURES (4706)
Primary Presenter: Jacquelyn Veatch, Rutgers University (jveatch@marine.rutgers.edu)
Food resources in the ocean are relatively diffuse, and need to be concentrated for consumers. This is done, in part by mesoscale and sub mesoscale oceanographic features transporting and locally concentrating plankton, creating patchy regions of high prey availability. Lagrangian approaches applied to coastal ocean dynamics can identify the transport features responsible for plankton patchiness, linking highly nonlinear coastal flow to the spatial ecology of food webs. This study employs two Lagrangian coherent structure approaches, Finite Time Lyapunov Exponents (FTLE) and Relative Particle Density (RPD), to coastal surface currents observed by High Frequency Radars (HFR) around a known biological hotspot, Palmer Deep Antarctica. FTLE and RPD results were compared to the spatial ecology of phytoplankton, zooplankton, and foraging penguins, relating each level of the food web to lagrangian transport. Simultaneous measurements of the physics and food web were gathered through the integration of vessel and autonomous glider surveys within the HFR footprint. Results show FTLE better define borders of plankton patches while RPD better define centers of plankton patches that are then targeted by penguins. Transport features quantified by FTLE and RPD deliver and concentrate constant supplies of plankton, maintaining prey resources. Results will inform future work in the identification of biophysical interactions in more complex food webs, and expand the use of HFR data to track spatial ecology.
09:00 AM
REDUCED CONNECTIVITY BETWEEN KELP FORESTS UNDER ANTHROPOGENIC WARMING (5076)
Primary Presenter: Mirjam van der Mheen, University of Western Australia (mirjam.vandermheen@uwa.edu.au)
The Great Southern Reef is a system of interconnected kelp reefs that runs along the southern half of Australia. On the west coast, the reef runs from north to south, extending over 800 km in latitude. The northern range edge was highly fragmented and partially lost during the 2011 marine heatwave, with little to no recovery. The poleward flowing Leeuwin Current is the main driver for kelp dispersal and connectivity between the reef systems in this region and can typically transport drifting material over 200 km within 30 days. Kelp can disperse in two main ways: through dispersal of zoospores and detached fertile material. Detached fertile drift material can disperse over longer distances and provides the greatest potential connectivity between reef systems. However, detached kelp material decomposes over time, and laboratory experiments show that decomposition rates vary significantly with temperature, from the order of several days in warm conditions to hundreds of days in cool conditions. This potentially has considerable implications for the connectivity of kelp reef systems under anthropogenic warming conditions. Here we combine Lagrangian particle tracking simulations with known kelp decomposition rates to show how the connectivity between kelp reefs along the west coast of Australia will change under future climate change scenarios. We show that connectivity may decrease with warming, which has implications for the resilience of kelp forests, potentially limiting processes such as genetic rescue and the recovery of lost kelp forests following extreme events.
09:15 AM
The pathways of plastic in the Mediterranean Sea and its potential impact on marine biota (5465)
Primary Presenter: Alberto Baudena, Laboratory of Oceanography of Villefranche (alberto.baudena@gmail.com)
Plastic debris is a ubiquitous pollutant found from the sea surface to the seafloor. Understanding the mechanisms driving its pollution is a difficult task mostly due to the complex oceanic circulation, which affects plastic debris in manifold ways. The Lagrangian approach is hence a natural framework to study this problem. Here, I will show the results of TrackMPD, a Lagrangian model simulating the pathways of plastic debris in the Mediterranean Sea, and validated with the most extensive dataset of plastic measurements in this region to date. The Mediterranean Sea lacks in zones of plastic accumulation despite being one of the most polluted basins worldwide. Here, we adopt a different paradigm, by identifying crossroad regions through which large amounts of plastic debris flow. We find that around 20% of Mediterranean plastic debris passed through 1% of the basin surface. The most important crossroads intercepted plastic debris from multiple sources, which had often traveled long distances. During its travel, plastic debris can be colonised by marine organisms, and eventually sink. We found that the locations where debris leaves the surface are significantly different from those where it reaches the seafloor: debris travels hundreds of kilometers during its sinking. In the water column, plastic debris can potentially be mistaken for zooplankton and be ingested, thus impacting marine biota. To quantify this risk, we estimated the plastic debris to zooplankton ratio over the entire Mediterranean Sea, showing a high risk of contamination for both pelagic fish and whales.
09:30 AM
Lagrangian transport of cold stunned Kemp’s ridley turtles stranding on the Dutch coast (5282)
Primary Presenter: Darshika Manral, Utrecht University (d.manral@uu.nl)
Kemp’s ridley turtles (Lepidochelys kempii) are the smallest and the most endangered of all the sea turtle species. Although their native habitat is restricted to the Gulf of Mexico and east U.S. coast, occurrences of juvenile Kemp’s ridley turtles in the north-western European coasts have also been documented in the past, particularly in winter months. Since turtles are ectotherms, hypothermic conditions during winter induces sluggish behaviour in them and they lose their ability to actively swim, a condition termed as ‘cold stunning’. For Kemp’s ridley turtles, cold stunning is known to occur below ocean temperatures of 10-12°C, causing them to float at the surface ocean. Knowledge on the dispersion of these cold stunned turtles can help improve their rehabilitation success rate in the Netherlands. In this study, we perform Lagrangian modelling of surface ocean transport of juvenile turtles that were found stranded alive on the Dutch coast in cold stunned state over the last 15 years. We find that these turtles enter through the English Channel and only first encounter cold conditions from a few days to a months’ time before stranding.
09:45 AM
ENHANCED BIOLOGICAL ACTIVITY IN LAGRANGIAN COHERENT EDDIES OF THE NORTH PACIFIC SUBTROPICAL GYRE (5530)
Primary Presenter: Alexandra Jones, MIT-WHOI Joint Program in Oceangraphy (jonesae@mit.edu)
Mesoscale eddies modify the vertical structure of the resource environment for phytoplankton and also affect the horizontal dispersal and mixing of populations. Lateral trapping can intensify the signature of eddy-scale phytoplankton blooms and modify community structure by limiting mixing with surrounding populations. We address the hypothesis that coherent eddies, which trap material, will exhibit more intense chlorophyll blooms than leaky eddies due to reduced lateral dilution. We employ a Lagrangian approach, which provides metrics of the material coherence, to identify and track coherent vortices over two decades of remote sensing observations in the North Pacific Subtropical Gyre. We co-locate satellite ocean color data in eddies and find enhanced chlorophyll in both cyclonic and anticyclonic coherent eddies relative to the background and dispersive eddies. Enhancement via eddy trapping is greatest to the south of 23N in fall and winter. Our results highlight that Lagrangian coherency enhances the chlorophyll signature of North Pacific Subtropical Gyre eddies and that there are bio-physical differences seasonally and latitudinally.
SS095A Lagrangian Transport and Connectivity in Oceanic Flows: Applications to Ocean Dynamics and Marine Ecosystems.
Description
Time: 8:30 AM
Date: 5/6/2023
Room: Sala Ibiza B