ship-based
(proposed)
infrastructure
(proposed)
ship-based
(confirmed)
infrastructure
(confirmed)

BIOSWOT – Cape Cauldron

Understanding the ocean fine-scale processes and how they affect the atmosphere, the marine biodiversity, and the global climate in a highly energetic region.

The Cape Basin is a key hotspot for ocean, atmosphere, climate and biodiversity. The region is influenced by the largest levels of turbulence observed in the world ocean, which play a key role in the transport and mixing of the upper 1500 m layer of water masses entering the area from the Indian and Southern oceans making them especially relevant for the uptake and transfer of heat and salt and carbon. Cape Caudron, South Eastern Cape Basin, is characterized by very large and persistent eddies (rings) of ~100 km size, and it is also a hotspot for air-sea exchanges at the ocean fine scales. The region is also a very important hot-spot of marine biodiversity centered on the Benguela Large Marine Ecosystem, one of the most intense eastern boundary upwelling systems of the world ocean. 

Several aspects of the ocean dynamics at in the region are still unresolved. For example, what are the roles of the ocean fine-scale and air-sea exchanges in the uptake of heat, momentum, and carbon? What is the exact role of vertical transfers versus lateral steering and advection in setting the properties of water masses and how they penetrate in the ocean interior? What is the role of the ocean fine-scales in prescribing the plankton diversity and connectivity? 

Surface currents (left panel) and relative vorticity ( ζ=vxuy) normalized by Coriolis frequency (f) (right panel) for the Cape Basin study site with SWOT grid overlaid (black lines). Images were generated using output from a high-resolution MITgcm simulation and are instantaneous snapshots from 1 July 2012.

The BIOSWOT – Cape Cauldron campaign will take place during the SWOT fast-sampling phase. A large in situ internationally coordinated experiment will bring three ships instrumented with classical oceanographic sensors, but also fast sampling sensors, atmosphere sampling capacity, and a large number of autonomous ocean and atmosphere platforms. The experiment will also benefit from plankton observations by different means. Genetics analyses will be undertaken in collaboration with other international research projects and will allow characterizing biodiversity versus environmental conditions. This kind of analysis will also enable us to improve our understanding not only of the physical carbon pump but also of the biological carbon pump. Numerical studies with a hierarchy of physical, biogeochemical and throphic models will be either set up or, when already existing, analyzed for complementary studies in link with various national and international projects. The sampling philosophy of the BIOSWOT – Cape Cauldron experiment will be based on and expands the successful EUREC4A-OA approach to enable the observation of different scales, including the upper-ocean submesoscales, and this simultaneously in the ocean and the atmosphere. The daily planning will be guided by satellite imagery and weather forecasts and all this automatically retrieved and analyzed on board. 

Results from the BIOSWOT – Cape Cauldron campaign and from the BIOSWOT – Med campaign, carried out in a highly energetic and low energetic region respectively, will complement each other and will advance our understanding of the ocean fine-scale processes and how they affect the atmosphere, the marine biodiversity and the global climate. 

Principal investigators: S. Speich (LMD, ENS), X. Carton (LOPS, Brest), G. Lapeyre (LMD-IPSL) L. Renault (LEGOS) J. Boutin (LOCEAN-IPSL), G. Reverdin (LOCEAN-IPSL), N. Lefevre (LOCEAN-IPSL), C. Bowler (IBENS), T. Lamont (DEFF, South Africa), J. Huggets (DEFF, South Africa), S. Swart (Univ. Gotebörb, Suède), L. Beal (RSMAS, USA).

Contact point for the study site: Sabrina Speich (sabrina.speich@lmd.ens.fr) (LMD, ENS)