Calypso Coherent Lagrangian Pathways from the Surface Ocean to Interior

Scientific Discipline: Physical Oceanography

Research Area: Balearic Sea

Research Vessel/Equipment: RV Pelagia

PI Name and Affiliation: Dr Shaun Johnson, University of California, San Diego

Date: 20 Feb - 12 March 2022

Citation from PI: To adaptively sample the area of downwelling (with 1-10 km extent) at evolving (typically over about 1-2 days) ocean fronts requires both high spatial and high temporal resolution, which is hard to do from one ship. Therefore, we have assembled a two-ship operation aided by arrays of autonomous platforms (gliders, floats, drifters, and AUVs). Eurofleets+ support was critical in providing time on RV Pelagia from NIOZ.

Calypso Cruise Area

Abstract & Main objectives: The Coherent Lagrangian Pathways from the Surface Ocean to Interior (Calypso) project addresses the challenge of observing, understanding and predicting the 3D pathways by which water from the surface ocean makes its way deeper. Discovering the routes by which physical and biogeochemical tracers are transported vertically, as currents carry them horizontally, is our goal. Physical processes redistribute heat, salt, and biogeochemical properties with considerable impact on primary productivity. Comprehensive observations are combined with process study models and predictive models to identify coherent 3D pathways and to diagnose and predict the underlying physical processes of subduction.

Schematic showing downward-going filaments enriched in phytoplankton and oxygen at the edge of a gyre. Calypso aims to measure and characterize such subducting structures.

Atlantic water flowing out of the Strait of Gibraltar forms a set of gyres (black current vectors) with strong density fronts on their cyclonic/dense side. Flow converges at these fronts (divergence scaled by f from a WMOP forecast is the coloured background), which makes them likely sites for downward transport of surface water and thus the focus of Calypso. WMOP is a 1.5 km resolution real time regional operational model developed at SOCIB / IMEDEA. The schematic shows the scale of the observations (shown at different locations only for clarity). Experimental components include a fleet of 8 gliders (pink lines) spanning the Almer´ıa-Or´an front for 2–3 months and focused ship surveys (pink lines) with large arrays of surface drifters (coloured arrows) that guide biological tracer measurements, Lagrangian float deployments, and a profiling float array. Similar forecasts and satellite data will guide the deployments in real time.

Calypso expects to address specific questions about (a) dynamics, (b) Lagrangian trajectories, and (c) parameterizations: (a) What are the dynamical mechanisms by which water parcels are irreversibly subducted? What is the character of 3D fluid transport structures? What are the length and time scales, and coherence of the subducted features? Where do the subducted parcels end up?

(b) How does the predictability of particle trajectories vary in space and time? How does the presence of submesoscale features affect Lagrangian predictability based on models that only resolve larger scales? How can the 3D Lagrangian transport structures and trajectories be related to surface features that can be discerned from altimetry and general circulation models?

(c) How does knowledge of trajectories in 3D help us to better grasp and parameterize scalar transport and mixing processes where strong vertical motion exists?

Further Information available here: https://calypsodri.whoi.edu/