WHIRLS: The impact of ocean fine-scale whirls of climate and ecosystems

PIs: S. Swart, A. Biastoch, S. Fawcett, S. Speich

WHIRLS is an ERC Synergy project about small-scale ocean processes having large-scale impacts. Heat and carbon are the currencies of regional and global climate, constantly exchanged between the ocean and the atmosphere. This exchange is strongly influenced by fine-scales ocean eddies—whirls—that flux heat and carbon towards, or away from, the air-sea interface.

Satellite view of the ocean ‘whirls’ (ocean eddies and jets) that are fundamental to understand in the project. In this view, phytoplankton blooms act as tracers of the ocean fine-scale circulations. Image: NASA/Ocean Biology Processing Group  

WHIRLS will use an interdisciplinary approach to study fine-scale processes across a continuum of scales (1–100 km) and assess their impacts on air-sea exchange and marine biogeochemistry and biodiversity. We focus on the Agulhas Current System because it is a global hotspot of eddy activity, ocean-atmosphere heat exchange, and marine productivity and diversity. It is also a region that plays a key role for the global ocean circulation and global climate and climate change. We will use multiple coordinated observing strategies, including research vessels and a large ensemble of autonomous platforms, to collect physical, chemical, and biological datasets across scales. These data will be supplemented by high-resolution models of the ocean and the atmosphere as well as the latest data science methodologies. 

This view of relative vorticity (fluid rotation) in the km-scale model INALT60 that will be used in WHIRLS. Credit: Arne Biastoch, GEOMAR

The point of the ERC Synergy Grant is to bring together researchers with different expertise to work on very complex problems that no person or institute can address on its own. We are 4 PIs that bring together our teams and collaborators to tackle this complex issue. Arne Biastoch – GEOMAR, Kiel, Germany, Sabrina Speich – Ecole Normale Supérieure, France, Sarah Fawcett – U. Cape Town, South Africa, Seb Swart – U. Gothenburg, Sweden

Funding: ERC Synergy, €12M – 2024-2030

QUICCHE: QUantifying Interocean fluxes in the Cape Cauldron Hotspot of Eddy kinetic energy

PIs: L. Beal, K. Donohue, Y. Lenn, S. Swart, C. Roman

The Cape Basin in the southeast Atlantic is a global hotspot of eddy kinetic energy, fed by a leakage of waters from the subtropical Indian Ocean via the Agulhas Current. A proportion of warm and salty Agulhas waters are vigorously stirred and mixed into the cooler and fresher Atlantic by co-interacting rings and eddies.  Recent studies suggest that most Agulhas leakage is found outside these rings. We hypothesize that a large proportion of the Indian Ocean waters that leak into the Atlantic are to be found in submesoscale features generated by the mesoscale strain field. Observations of these features are lacking, as are estimates of the fluxes they affect. To fill this gap we propose to:

(1) Observe and characterize submesoscale features generated by the mesoscale eddy strain field. (2) Make novel estimates of Agulhas leakage with new observations, using theoretical eddy diffusivity and eddy flux frameworks. (3) Relate diffusivity and fluxes to new (SWOT) and existing satellite altimeter observations to infer variability in Agulhas leakage.

Funding: National Science Foundation (NSF), Swart funded by Wallenberg Academy Fellowship

PI: S. Swart

The seas surrounding Antarctica are where vast amounts of heat and carbon exchange between the atmosphere and the deep ocean. The physical processes in the Southern Ocean that underpin these exchanges ultimately determine the rate of climate change and therefore mitigation measures. Despite outstanding progress in observational techniques, there are extremely few observations, which has led to arguably the largest knowledge ‘blind spot’ in global ocean-climate research and predictability.

Specifically, new evidence suggests we urgently require to understand highly energetic upper ocean flows and instabilities (called submesoscale eddies and fronts, which evolve at scales of 0.1-10 km and hours-days). Through enhanced vertical exchange of properties, these phenomena change upper ocean mixing and stratification, thereby amplifying heat and carbon exchange at the air-sea interface. The changes in stratification by submeoscale processes can directly alter the transport of these climate-acute properties to the ocean interior, where they are stored at centennial timescales. Critically, contemporary understanding of these processes occurring in the sea ice regions surrounding Antarctica are severely poor due to a dearth of field data. This, in turn, has led to global climate models experiencing the greatest biases of key processes in the Southern Ocean.

To undertake this scientific challenge, we will coordinate state-of-the-art field observations and fit-for-purpose modelling experiments, including deploying under-ice capable ocean robots from ice breaker expeditions. A new ocean topography satellite mission will provide unprecedented high-resolution ‘surface views’ of the submesoscale processes. These cornerstone observations will be combined with models, of varying complexity, to provide new knowledge on how sensitive ocean-ice processes are to our changing climate and thereby improve climate prediction.

Funding: Wallenberg Academy Fellowship Extention – Knut and Alice Wallenberg Foundation – 2021-2026

PI: M. du Plessis; Host: S. Swart; Collaborators: S. Speich, B. Ward

In SPICE, our aim is to enhance our knowledge of oceanic heat and carbon uptake in the Southern Ocean in order to reduce uncertainties in future global climate model projections. Using ocean observations from state-of-the-art autonomous platforms and high-resolution numerical simulations, we will 1) quantify the variability of heat and carbon air-sea fluxes in the Southern Ocean and 2) better understand how ocean submesoscale processes modulate heat and carbon exchange between the atmosphere and ocean interior. These findings will enhance our understanding of both contemporary and future climate and will provide a benchmark for future research to critically assess climate models – an exercise vital to improving forecasts and thus mitigating against the effects of our changing climate.