# Projects

### Frontogenesis and Subduction at the Alboran Fronts

Amala Mahadevan, Mara Freilich, Mathieu Dever
Woods Hole Oceanographic Institution

The goals of Calypso are to unravel the three-dimensional coherent pathways by which water carrying tracers and drifting objects is transported from the surface ocean to depths below the mixed layer. The vertical movement of water from the surface to depth across the base of the mixed layer has implications for the transport of properties, gases, biogeochemistry, and the fate of drifting particles and objects. But, vertical velocities are very weak (about a thousand times smaller than horizontal velocities) and difficult to detect. This proposal will use modeling and observationally motivated process studies to address the following questions:
• How are water and properties from the surface boundary layer exported to depth?
• What coherent pathways act as conduits for exchange?
• What dynamics shapes these pathways? What are the Lagrangian trajectories, what are the time and space scales of subduction and where does the water end up?

### Vertical velocity in submesoscale streamers from spatial surveys following a profiling float array

Shaun Johnston
Scripps Institution of Oceanography

Goals. This project will use a combination of rapid spatial surveys from a ship and a rapidly-profiling float array to assess w at an intense front across a range of scales: (a) at mesoscale from the spatial surveys using quasigeostrophic approximations, such as the omega equation, (b) in submesoscale streamers by tracking tracers (such as chlorophyll, salinity, spice, and potential vorticity) with finer spatial surveys and a float array, and (c) in submesoscale streamers by acoustically tracking isopycnal-following floats, and (d) due to internal waves from each float's displacement fluctuations.

Plan. Repeated meso- and submesoscale-resolving surveys in the upper 200 m with Underway CTD (UCTD) and/or SeaSoar will follow an array of up to 8 SOLO-II floats at a mesoscale front and submesoscale streamers on its flanks during 3 cruises. A feature will be identified in an initial mesoscale UCTD or SeaSoar survey, a forecast model, and near-realtime satellite products, e.g., sea surface temperature and chlorophyll. The float array will be deployed in a submesoscale streamer in a box pattern and recovered after several days. Each float profiles to 200 m every 100 minutes and obtains about 400 profiles over a 30-day cruise. The submesoscale UCTD survey will follow the float array at the front. Cross-front sections of about 20-km length will be completed every 6 hours. Along each section, temperature and salinity profiles will be obtained at a horizontal resolution of about 250 m every 4 minutes. The whole suite of observations (mesoscale survey, float array, and submesoscale survey) will be relocated and repeated.

### Identification and Real-Time Tracking of Fronts and Subduction Zones Through Deployments of Massive Arrays of Biodegradable Drifters

Tamay Ozgokmen
University of Miami

The proposer spent the past 5 years advancing drifter-based ocean sampling to a massive scale by releasing some 2500 drifters in the Gulf of Mexico under four major expeditions. One of the primary findings of these expeditions is that the ocean's surface is covered by convergence zones and fronts containing high vertical velocities [O(1 cm/s)]. Yet these convergence zones are very narrow [O(100 m)] and very rapidly evolving [O(1 hour)]. Drifters are the only instruments that can locate and track these features in real-time accurately. GPS-tracked drifters naturally provide circulation data without any interruptions and far longer than the ship time used in ocean expeditions. The massive data sets in the Gulf (close to 20 million velocity points) were made possible through the development of a new type of drifter, which is biodegradable, compact, cost-effective, and scalable to hundreds of deployments over a few hours (patent for \"Ozg\"okmen and co-inventors). More recent versions of the drifter include temperature, salinity and wave sensors, as well as drogues of different lengths. I propose to bring this new capability to the ONR-DRI experiments. When combined with other instruments, in particular the Lagrangian floats, it will present an essential tool to begin addressing the scientific questions posed in the white paper.

### Theory, modeling and observations of 3D transport processes in flows with fronts

Larry Pratt and Irina Rypina
Woods Hole Oceanographic Institution

We propose a combination of filed measurements, theory and modeling, all aimed at contributing to CALYPSO through experimental design, Lagrangian observations, and interpretation of results. A large part of CALYPSO will focus on understanding subduction processes near a western Mediterranean front, and investigating how physical and biological properties are transported from the surface down below the mixed layer. Fronts are often established by a larger scale convergence, but the sinking process might be dominated by the smaller-scale ageostrophic secondary circulations that are established in the vicinity of the front. A number of different frontogenetic and instability processes may contribute to the 3d transport, and our observations and analysis should help to disentangle the relevant processes and to identify which are dominant. We specifically propose novel measurements with drifters drouged at a variety of depths in order to observe the horizontal component associated with subduction of fluid under the front, and to infer the vertical motions. We also plan to release environmentally friendly dye as part of a US trial experiment in order to directly observe the lateral and vertical transport. On the theoretical/modeling side, we want to examine vertical motion associated with spatially-growing meanders of the front, as spatial/convective instability seems important for the Almeria-Oran front. We also want to employ a model of the Alboran Sea (based on the MITgcm) that our graduate student has developed. This will allow us to test our idealized stability calculations in a more realistic setting. We will collaborate closely with Ruth Musgrave on analyzing her non-hydrostatic, ultra-high-resolution model output, focusing on investigation the role of small-scale motions in the resulting 3d processes near a front. Finally, since the transport of surface properties down to depth is an essentially Lagrangian problem, we will apply state-of-the-art analysis from a recent MURI project (OCEAN 3D+1) to both model output and data in order to identify the Lagrangian skeleton of the ageostrophic circulations that cause subduction. In this way, we hope to create a transition between OCEAN 3D+1 and CALYPSO.

### Observations of three-dimensional frontal circulation using underwater gliders

Dan Rudnick
Scripps Institution of Oceanography

The circulation across oceanic fronts has been a topic of study for decades. The strain that causes fronts necessarily results in a cascade from mesoscales of the size of oceanic eddies down to submesoscales of 1 kilometer size and smaller. In particular, the three-dimensional flow at these small scales may be intense. These flow are difficult to observe because of they are so small, intense, and intermittent. Here, we propose an observational plan using underwater gliders to address the following goals:

• to quantify mesoscale vertical velocity using survey data and diagnostic approaches
• to resolve submesoscale three-dimensional flow through direct measurement
• to observe internal wave vertical displacements around a front

We propose to use Spray underwater gliders to observe these processes. Gliders will be used first to survey in a coordinated fashion. We plan to contribute six underwater gliders to a collaborative fleet that may be as large as 15 gliders. In survey mode, the 15 gliders would cover the same track length per unit time as a ship surveying with a towed vehicle. Deployments will last 100 days profiling to 1000 m, and gliders will carry sensors to measure temperature, salinity, velocity and chlorophyll fluorescence. Second, we propose to take advantage of our ability to park a Spray on an isopycnal in the region of a front, and measure vertical velocity through changes in pressure. We propose to use 3 gliders in this way, to produce a maximum of about 50 three-day drifts. A proposed technical development is to equip the gliders with acoustic tracking equipment to realize complete 3-dimensional flow during the drifts.
A timeline is as follows. Year 1 will include a pilot experiment in the Alboran Sea using one glider and the development required to integrate acoustic navigation onto Spray gliders. Year 2 will include the remainder of acoustic integration, and intensive sampling using six gliders. A second intensive experiment will take place during year 3, again using six gliders. Years 4-5 will focus on analysis, and presentation and publication of results.

### AUV Observations of Small-scale Frontal Convergence

Andrey Shcherbina and Craig McNeil
University of Washington

Objectives: To map the sub-kilometer structure of temperature, salinity, 3D velocity, and natural passive tracer distributions associated with the convergence at the Alboran Sea salinity front using a pair of REMUS Autonomous Underwater Vehicles (AUVs) actively following Lagrangian pathways of frontal subduction.
Proposed study directly addresses some of the main CALYPSO DRI objectives by:
1. Characterizing 3D coherent structures responsible for frontal subduction and exchange between the surface and the interior,
2. Directly measuring spatial and temporal variability of small-scale horizontal and vertical velocities associated with these structures,
3. Quantifying surface convergence and relating it to the vertical structure of interior transports,
4. Developing new techniques for adaptive autonomous multi-vehicle ocean exploration.
The study builds upon the new scientific understanding, experience, and techniques we developed during our ongoing work in the ONR Undersea Remote Sensing (USRS) DRI, as well as the recent work funded by the Gulf of Mexico Research Initiative (LASER and SPLASH experiments).

### The role of high Rossby number processes on vertical pathways in the upper ocean

Ruth Musgrave
Woods Hole Oceanographic Institution

A study of vertical pathways in the upper ocean at scales from $\mathcal{O}$10 m - 1 km is proposed, where the high relative vorticities of surface flows lead to high Rossby numbers processes such as filaments and vortices. These processes are not quasigeostrophic and their vertical velocities cannot be determined using established quasigeostrophic methods (i.e. the omega-equation). They arise in the forward cascade of energy from low Rossby number features, and vertical velocities associated with them are expected to have larger magnitudes but shorter timescales than those governed by quasigeostrophic dynamics. This work will address outstanding questions relating to the role of high Rossby number processes and their associated vertical velocities on advective pathways in the upper ocean, using both observations and numerical models. ///// The observational component of the proposed work will employ ship-based bow chain surveys in the western Alboran Sea to make measurements of temperature, salinity, fluorescence and oxygen at extremely high horizontal resolution ($\sim$ 1 m) in the upper ocean at relatively high ship speeds (10 kn), reducing issues of space-time alias that have challenged prior studies using this technology. Concurrent work will examine high Rossby number processes in a series of nonhydrostatic idealized numerical models of a baroclinically unstable front, with parameters close to those observed in the western Alboran Sea. The simulations will both aid interpretation of the bow chain measurements and also quantify the influence of model resolution and nonhydrostatic processes on vertical pathways in frontal regions. Through collaboration with other DRI members, particle trajectories, Lagrangian pathways and barriers, and particle clustering and dispersion will be assessed in these simulations. The comparison of Lagrangian metrics at different resolution will enable an assessment of the accuracy of vertical pathways determined in lower resolution, regional numerical models.

### Multiscale modeling of vertical and horizontal dispersion of material by submesoscale motions in frontal regions

Sutanu Sarkar
UC San Diego

Vertical transport from surface to depth in the upper ocean presents a challenge to both measurement and and prediction because of its small magnitude, its spatiotemporal intermittency and its uncertain links to environmental forcing. Recent and ongoing work points to the importance of coherent eddy-driven flow convergences in mediating vertical transport. The vorticity and strain increase as the length scale of the eddying motion decreases towards the submesoscale but the time scale over which the flow field remains coherent also changes with decreasing length scale in a manner that is poorly understood. We propose numerical simulations of frontal regions that are seeded with an ensemble of floats to study the space-time behavior of submesoscale eddies. High spatial resolution of O(m) will be employed in all directions to capture the multiscale nature of submesoscale vortices (the hotspots of coherent vertical transport) as well as filaments with high turbulent dissipation rate. The associated horizontal and vertical dispersion of floats will be obtained in idealized simulations of baroclinic instability as a function of frontal strength, stratification and wind forcing. Supplementary simulations steered by observations of fronts in the proposed DRI site (western Mediterranean) will be conducted. Lagrangian particles will be compared with floats that deviate from truly Lagrangian tracking owing to inertia and buoyancy. The simulation results will be analyzed using Lagrangian statistics, multiscale diagnostics and, in collaboration with other DRI investigators, also tools of Lagrangian chaos theory.

### Development and Innovation of Lagrangian Drifters in Support of ONR Activities

Luca Centurioni
Scripps Institution of Oceanography

The use of near-surface Lagrangian drifters to measure ocean currents is more than a century old and a global array of drifters, termed the Global Drifter Program, is maintained by the PI of this proposal. The array is rather sparse, with a nominal resolution of 5°X5° and in excess of 25,000 drifters have been deployed to date. Several ONR projects requires higher spatial resolution to address a variety of science questions. In its basic configuration, the Surface Velocity Program (SVP) drifter measures only SST and ocean currents at a depth of 15 m (i.e. the center-depth of the drogue). With a lifespan of two years, the SVP drifter design measures 15 m depth currents with unmatched accuracy and has the best cost effectiveness compared to other drifter designs. The SVP Barometer (SVPB) drifter has the same capability of the SVP drifter but it also carries a barometer to measure atmospheric sea level pressure. Innovating the Lagrangian drifter technology plays a crucial role in maintaining an efficient and modern global array for climate monitoring, numerical weather prediction and satellite SST Cal/Val. and for addressing specific science questions in regional experiments. With the proposed effort, we seek funds to develop new drifters by expanding the computing power of the instrument, the range of hosted sensors and their duty cycle. In support of the next generation Surface Velocity Program drifter, the LDL proposes to modernize the architecture of the embedded buoy controller with on-board Wi-Fi capabilities. We also propose the development of an in-house inductive communication system to replicate functionality of commercially available options. The new drifter board that will be developed with this effort will have a powerful enough processor and RAM to allow for onboard data reduction and the new developed inductive module will then be used to integrate chi-pods and drifting thermistor chains. SVP, SVPB, CODE and ADOS drifters will be fabricates in support of ONR science efforts.

### Three Dimensional Lagrangian Trajectories

Eric D'Asaro and Andrey Shcherbina
University of Washington

We propose experimental work that directly addresses the observational objectives of the DRI by 1) Measuring three-dimensional Lagrangian trajectories of water parcels originating in the mixed layer and subducting at submesoscale fronts using Lagrangian floats. 2) Measuring the evolving temperature, salinity and velocity along the trajectory from float-mounted sensors, including a new ADCP, and from these, infer mixing rates along the trajectories. 3) Collaborating with other CALYPSO investigators, both theoretical and observational, to optimize the location of these measurements and place them in a mesoscale, submesoscale and dynamical context.

### Modeling Coherenet Lagrangian Pathways from the Surface Ocean to the Interior

James McWilliams and Peter Sullivan
UCLA, UCAR

This project uses numerical simulations of messocale, submesoscale, and microscale turbulent flows to investigate the controlling process for material transport from the oceanic surface mixed layer into the stratified interior. The goals are phenomenological discovery, dynamical understanding, and guidance for field experimental design and measurement interpretation. The modeling tools are the Regional Oceanic Modeling System (ROMS) in either hydrostatic or nonhydrostatic mode and Large-Eddy Simulation (LES).

### Coherent Lagrangian Pathways in 3D+1 Submesoscale Transport in CALYPSO

Helga Huntley and Denny Kirwan
University of Delaware

The DRI CALYPSO aims to identify the connections between mesoscale signatures, submesoscale processes, and Lagrangian pathways in order to improve understanding and predictability of the exchange of water and properties from the surface to depths below the mixed layer. In this context, we seek to address two key questions during the first three years of CALYPSO: First, how strong are vertical velocities in a submesoscale-rich environment near a salinity front, how do they impact the dominant 3D submesoscale coherent Lagrangian pathways (CLP), and what specific dynamical processes produce them? Second, how can these ephemeral transport channels be identified? Specifically, what surface signatures are tell-tale signs of vertical exchange?

We propose to undertake two tasks. The first is to characterize the vertical velocities from measurements and modeling. Vertical velocities will be measured directly during CALYPSO, but they can also be derived from horizontal divergence estimates from surface drifters. Moreover, since the drifters are expected to have different drogue depths, we will be able to assess the vertical gradients of divergence and the other kinematic properties. To compare model and observation estimates of vertical velocities and kinematic properties in the vicinity of fronts, we propose to collaborate with modelers. The model data will also permit a quantitative assessment of the role of the vertical velocity in determining CLP.
As a second task, we will construct coherent 3D+1 Lagrangian pathways from the surface through the mixed layer and identify surface signatures. This will also be performed in collaboration with modelers, whose 3D model velocity fields will be used to compute fully 3D time-varying finite-time Lyapunov exponents (FTLE) and to link surface phenomena to vertical pathways. Repeating this at multiple grid resolutions will allow us to evaluate how robust the CLP are. The contextual synoptic data in the model will also provide insight into the mechanisms by which water and associated properties are exported from the surface to depth and into the role that CLP play in this. Furthermore, we seek to stitch layer-wise analysis of drifter data together into an observed 3D time-varying picture of the CLP.

An additional two-year option would allow us to address a third basic question: How can the predictive skill of general circulation models (GCMs) for 3D coherent Lagrangian pathways be improved? The approach is to blend Lagrangian and other appropriate data with high-resolution forecast models to improve Lagrangian predictability. Surface phenomena identified as being characteristic of subduction pathways will be targeted. Initial experiments will be carried out with parallel model runs. When possible, appropriate observational data from the field campaigns will be blended with GCM forecasts.

### Measurements of Upper-ocean Velocity and Hydrography Structure During CALYPSO

Tom Farrar
Woods Hole Oceanographic Institution

We propose to study oceanic variability near a strong oceanic front in the Coherent Lagrangian Pathways from the Surface Ocean to Interior (CALYPSO) Departmental Research Initiative (DRI). Our focus will be on resolving the full range of “submseoscale” variability at horizontal scales of 1m-10km using a novel technique for obtaining high-resolution transects of temperature, salinity, and velocity measurements at relatively high ship speeds (up to 10kts, though initial efforts will start at slower speeds). The tow-body/instrument-chain effort will be in close collaboration with the CALYPSO project proposed by Ruth Musgrave (WHOI). We will also support the CALYPSO effort with Underway Conductivity-Temperature-Depth measurements (UCTD). The scientific interpretation will be in collaboration with other CALYPSO investigations.

### 4D-LANES: Four-Dimensional Lagrangian Analysis, Numerics, and Estimation Systems

Pierre Lermusiaux
MIT

Vertical transport from surface to depth in the upper ocean presents a challenge to both measurement and prediction because of its small magnitude, its spatiotemporal intermittency and its uncertain links to environmental forcing. Recent and ongoing work points to the importance of coherent eddy-driven flow convergences in mediating vertical transport. The vorticity and strain increase as the length scale of the eddying motion decreases towards the submesoscale, but the time scale over which the flow field remains coherent also changes with decreasing length scale in a manner that is poorly understood. We propose numerical simulations of frontal regions that are seeded with an ensemble of floats, to study the space-time behavior of submesoscale eddies. High spatial resolution of O(m) will be employed in all directions to capture the multiscale nature of submesoscale vortices (the hotspots of coherent vertical transport) as well as filaments with high turbulent dissipation rate. The associated horizontal and vertical dispersion of floats will be obtained in idealized simulations of baroclinic instability as a function of frontal strength, stratification and wind forcing. Supplementary simulations steered by observations of fronts in the proposed DRI site (western Mediterranean) will be conducted. Lagrangian particles will be compared with floats that deviate from truly Lagrangian, tracking owing to inertia and buoyancy. The simulation results will be analyzed using Lagrangian statistics, multiscale diagnostics and, in collaboration with other DRI investigators, also tools of Lagrangian chaos theory.

### Vertical velocities and 3D pathways

Annalisa Griffa
CNR, Italy

The goal of this proposal is to contribute to the understanding and prediction of processes of vertical transport from the surface to depth through the joint analysis of Lagrangian data at the surface and water column data from LADCP and microstructure glider.

The proposed research will contribute to the identification and characterisation of high vertical velocity regions and 3D pathways in the frontal area of interest in the South Western Mediterranean Sea. This will be achieved through the development of new methodologies and through the participation to the planning, implementation and analysis of the multiplatform experiments. The proposed work will be carried out along the following two main lines:

i) a targeted analysis of drifter data will be performed to identify surface convergence regions with high vertical velocities;
ii) thermohaline and microstructure properties in the corresponding interior regions will be characterised using a glider equipped with a Micro Rider, and estimates of vertical velocities

### Eulerian inflow observations for Lagrangian analyses of coherent structures using low-cost short-term real-time moorings

Uwe Send and Matthias Lankhorst
Scripps Institution of Oceanography

CALYPSO will study 3D LCSs in the front which usually forms in the eastern Alboran Sea, resulting from the confluence of the Algerian Current deflected into the East Alboran Gyre and the Northern Current which flows south along the French and Spanish coast. Our objective is to continuously observe these two inflow branches during the two targeted observing periods in 2019 and 2020. We will relate their confluence to frontal properties and provide upstream boundary conditions for assimilating models. The approach consists of using three “geostrophic” CTD moorings capturing both inflow branches, giving mass transports, shear/isopycnal slopes, and mean stratification (on hourly or faster time scales). For this we will test a new design of light-weight real-time low-cost moorings for short duration deployments in year 1, and in years 2 and 3 operate three geostrophic end-point moorings of this design during the targeted observing periods to capture the inflow and upstream boundary condition. We will provide data, in delayed-mode and in real-time, to CALYPSO modelers for hindcasts, nowcasts, and forecasts of the frontal region, and collaborate with partners to understand what constraints the inflow conditions can provide for 3D LCSs in this front. We will place the moorings based on previous-day altimeter maps, on real-time analyses of the flow field (from SOCIB and from the MIT MSEAS system), and based on planning for the frontal field work in the subsequent days. The moorings would remain deployed for the approximately 2-3 weeks of the intensive frontal surveys.

### Analyzing vertical ocean transport with Lagrangian coherent structures

Michael Allshouse
Northeastern University

Because the horizontal velocities are often an order of magnitude greater than vertical mixing, it can be difficult to quantify the vertical transport of material exclusively from Eulerian methods, so we propose the use of Lagrangian coherent structure analysis to provide a reduced order illustration of the pathways for transport from the surface to depth. The goal of this proposal is to develop a real-time method for identifying attracting coherent structures at the surface of the ocean that signal potential downwelling events occurring in the underlying water column. This requires the correlation of two-dimensional surface coherent structures to vertical transport below. We propose the use of classification of hyperbolic structures near the edges of materially coherent vortices as a signal of nearby vertical transport. Testing of this method on numerical ocean models will reveal the potential of these structures for predicting future vertical transport. A secondary objective of this proposal is to develop a drifter deployment optimization that best demonstrates both the horizontal and vertical transport near the density front.

### Uncovering Lagrangian transport features associated with oceanic fronts, meanders, eddies and filaments

Thomas Peacock
MIT

Employ and advance the latest Lagrangian transport data analysis tools to perform fundamental and applied studies of two- and three-dimensional transport in the vicinity of oceanic fronts, meanders, eddies and filaments. Inform and guide the planning and implementation of deployment strategies for the CALYPSO field programs and support interpretation of the field data.

### LAgrangian Measurements in the Eastern Alboran Sea (LAMEAS)

Pierre-Marie Poulain
CMRE, Italy

Our general objective is to improve our understanding on the 3D dynamics in the upper ocean through which water and properties are transported from the surface to depths below the mixed layer, by exploring the dynamics of a frontal area in the southwest Mediterranean Sea at scales ranging between 1 and 100 km using Lagrangian drifter observations. In particular, we propose to study the near-surface circulation and the thermohaline structure in the vicinity of a front separating the relatively fresh Atlantic and salty Mediterranean waters in the area east of the Alboran Sea (sometimes called the Almeria-Oran front) during two campaigns in summers 2019 and 2020. Both drifter experiments will last only a few weeks and will be integrated with, and complementary to, measurements collected by other CALYPSO DRI participants using other platforms (drifters, gliders, floats, research vessels). The sampling strategy will be optimized using satellite observations and numerical model simulations/forecasts. The study will focus on the near-surface expression of 3D coherent Lagrangian pathways, at sub-mesoscale and mesoscale levels. Analyses of the collected data will be both descriptive and statistical.

### Frontogenesis and Subduction at the Alboran Fronts

Simón Ruiz and Ananda Pascual
IMEDEA, CSIC, Spain

This proposal aims at unraveling the three-dimensional coherent pathways by which water carrying tracers and drifting objects is transported from the surface ocean to depths below the mixed layer. The Alboran Sea, which lies in the Western Mediterranean, is home to a quasi-permanent front that separates fresher Atlantic water entering the Mediterranean through Gibraltar, from the more saline and dense water of the Mediterranean. As the front intensifies, it generates an along-isopycnal vertical motion that is estimated to be of the order of 100 m per day. The objective is to measure or infer the frontal vertical velocity, estimate the associated vertical mass flux, and understand the physical mechanisms that lead to the vertical motion. A retrospective analysis based on satellite altimetry, SST, ocean color and surface salinity in the Alboran Sea will be performed, specifically addressing the identification of the Almería Orán front and its variability. Fieldwork will be carried out in collaboration with colleagues from Woods Hole Oceanographic Institution, Scripps and U. of Washington, who have submitted a proposal to ONR (US) in the frame of CALYPSO (Coherent Lagrangian Pathways from the surface ocean to Interior) Departmental Research Initiative. During three field experiments conducted in 2018, 2019 and 2020, the front will be mapped in detail, using a multi-platform approach: the thermosalinograph at surface, CTDs, ADCP, underway CTD, water samples, gliders, drifters, and buoys with subsurface ADCP to infer vertical velocity in the context of the frontal physics. A submesoscale permitting ocean model simulation (NATL60) will be used together with a process oriented model (PSOM, WHOI) and an analytical QG model (Tang) to understand the mechanisms in a time-evolving frame.

### 3D Pathways, vertical velocity and biogeochemistry at Alboran Fronts

Joaquín Tintoré and John Allen
Baptiste Moure, Eva Alou, Nikolaos Zarakanellos, Cristian Munoz, Inma Ruiz
SOCIB, Spain

Fieldwork will be carried out in collaboration with colleagues from Woods Hole Oceanographic Institution, Scripps and U. of Washington, who have submitted proposals to ONR (US) in the frame of CALYPSO (Coherent Lagrangian Pathways from the surface ocean to Interior) Departmental Research Initiative. During three field experiments conducted in 2018, 2019 and 2020, the Almeria-Oran front will be mapped in detail, using a multi- platform approach: one or two research vessels, depending on availability, ocean gliders, drifters, and buoys. SOCIB will enhance the modeling efforts of the IMEDEA and US teams by focusing on its experience with biogeochemical coupling in the Western Mediterranean and prioritizing its high resolution data assimilation objectives within its extensive programm of operational modeling. One major technology objective for SOCIB is the development and testing of optimized glider operations for a fleet of vehicles in a strong current environment. Glider deployment strategies and sampling parameters will take account of model predicted current profiles, extending the current work on the family of optimized glider trajectories into a fully three-dimensional volume sampling context.