WHIRLS : a new campaign at sea to measure small ocean eddies and their impact on climate and marine life

Satellite view of small ocean eddies off Cape Town, South Africa.

For decades, it has been assumed that motions smaller than the mesoscale would decay into turbulence, draining energy from the mean ocean circulation. From limited-area observations and new numerical modelling studies, it is now evident that energy can also transfer to larger scales — the inverse energy cascade —strengthening the circulation and enhancing vertical fluxes, as well as driving mixing.

WHIRLS will improve the understanding of fine-scale processes and its representation in future earth system models for better predictions and projections of the future climate. A team of four experts and their groups in physical oceanography, meteorology, biogeochemistry, and biology will form a multidisciplinary synergistic working team to study fine-scale processes across a continuum of scales (1-100 km) and assess their impacts on air-sea exchange, marine biogeochemistry and biodiversity. The Agulhas Current System around South Africa is a global hotspot of eddy activity, ocean-atmosphere heat exchange, and marine productivity and diversity and will thus be the focus of the WHIRLS studies.

WHIRLS focuses on the most energetic region of the world ocean, the Agulhas Current System. This system around South Africa is not only unique with respect to its vigorous circulation, intense air-sea heat and carbon uptake and the particularly high-productivity and diversity of the embedded marine ecosystem. It is also an important key region of the global overturning circulation by providing warm and saline Indian Ocean water that passes through the Cape Basin (southwest of Africa) into the Atlantic Meridional Overturning Circulation (AMOC), and thus has an important impact on regional and global climate change.

It is vital to resolve small-scale processes in climate models, thereby improving their accuracy in order to better predict climate change and develop appropriate mitigation and adaptation solutions.

Sabrina Speich, professor and project leader at ENS-PSL/LMD-IPSL Paris.

Scientists will address this holistically, via an original and interdisciplinary approach, the continuum of scales, from the submeso- (1–10 km) to the mesoscale (10–100 km), of ocean dynamics and air-sea interactions, as well as their implications for marine biogeochemistry, including the ocean carbon sink, and biodiversity. WHIRLS will unlock new knowledge, improve the modelling accounting of these phenomena, and thus augment their predictive skills to:

• Observe and model the physical and biogeochemical structure, evolution, and phenomenology of the ocean fine-scale in the upper 1000 m of the water column.

• Determine to which degree fine-scale ocean dynamics interact with the atmosphere to drive air-sea exchange of climate-relevant variables, and how they shape ocean productivity and marine ecosystems.

• Quantify the role of fine-scale dynamics in the large-scale ocean circulation and the climate-critical cycles of heat, water, and carbon.

• Improve future Earth system models by resolving or parameterizing submesoscale dynamics.

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