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Eastern Boundary Upwelling Systems (EBUS) Transverse Thematic


O. Astudillo, M-L Bachelery, C. Barus, I. Dadou, B. Dewitte, V. Garçon, K. Goubanova, I. Hernandez, S. Illig, C. Maes, A. Paulmier, J. Sudre, O. Vergara

A - Achievements over the present contract

Following recommendations provided by the previous AERES Scientific Committee in December 2009, the DYNBIO team developed strong ties with the ECOLA team on the research theme of exchanges between the shelf and the open ocean in upwelling zones. Scientists working on this same theme within both ECOLA and DYNBIO teams have actively animated the Eastern Boundary Upwelling Systems (EBUS) Transverse Thematic within an international framework, the Mid-Term Strategy Initiative on the EBUS from the SOLAS programme.

Scientific quality and outputs

Oxygen Minimum Zones (OMZs) as suboxic layers are known to play a key role on the evolution of the climate (greenhouse gases production) and of the ecosystems and fisheries (nitrogen loss, respiratory barrier for zooplankton and fishes). Despite their importance and the worrying problem of the ocean’s deoxygenation due to global warming and human activities, OMZs have not been extensively documented and studied. Current models exhibit severe biases in simulating the vertical and horizontal O2 OMZ distribution, although oxygen is one of the first measured oceanographic parameters. Within this axis, we have concentrated our efforts on the OMZ off Peru with the launch of the AMOP project in close partnership with Peru (IMARPE, IGP) and Germany (GEOMAR), and on the OMZ off Namibia/South Africa with the EU FP7 MEECE project in close partnership with Cape Town University in South Africa.

    The AMOP project (PI: A. Paulmier, DYNBIO Team, co-I : V. Garçon, C. Maes (DYNBIO), B. Dewitte (ECOLA), see http://www.legos.obs-mip.fr/recherches/projets-en-cours/amop) is based on the central hypothesis that physical and biogeochemical processes contributing to the maintenance and variability of the OMZ vary among the different layers of the OMZ with a special role played by the oxycline. The latter hosts an intense and intermittent biogeochemical activity (consumption of oxygen). The AMOP project aims to test this hypothesis in the OMZ off Peru in the Eastern South Pacific. AMOP is unique since it focuses only on the dissolved oxygen parameter and proposes to establish an O2 budget as complete as possible considering all of the physical and biogeochemical contributions. This goal required a multidisciplinary approach covering biogeochemistry, physics, acoustics, ecology and atmospheric sciences.
AMOP was articulated along two axes: a modeling platform
(FP7 European EUR-OCEANS Flagship www.eur-oceans.eu/?q=deoxygenation_flagship), and experimental efforts with national labelling LEFE-CYBER and LEFE-GMMC, and funding support from INSU/CNRS, IRD, LEGOS, IFREMER and the German SFB754.

The approach is based on: 1) a 30 day cruise on board the R/V L’Atalante associated with ARGO floats deployment (25 January 2013-23 February 2014, Chief Scientist: C. Maes DYNBIO), 2) a monitoring mooring ocean_deoxygenationon a historical fixed station coupling water column and sediment measurements, the mooring was deployed in early January 2013 from the German R/V Meteor and was recovered in late February 2014 from the R/V L’Atalante, 3) a modeling platform ROMS-BIOEBUS (EUR-OCEANS Flagship) in order to cover the spectrum of various time scales which were sampled or not and to assist with our data interpretation (from the in vitro to in situ and remote sensing observations).

The AMOP project is composed of 13 research and service laboratories in France, 2 institutes in Peru and 6 institutions in 5 other countries (Germany, Mexico, Spain, Denmark, USA) and operates as an international consortium on deoxygenation of the oceans. AMOP is a pilot project within the EBUS MTS with tight cooperation with our Peruvian and German (SFB754 project) colleagues. These different activities within the EBUS Transverse Thematic led us to organize 3 international workshops within the SOLAS science themes: Air-Sea gas fluxes at EBUS” at IMARPE in Peru (2010), the EUR-OCEANS Deoxygenation of the Oceans” Conference in Toulouse (2011), and “Towards an integrative regional coupling in the EBUS” at IGP in Peru (2012). We also co-organized the 46th Colloquium of Liège (2014) on “ Low oxygen environments in marine, estuarine and fresh waters”. B. Dewitte (ECOLA), A. Paulmier and V. Garçon (DYNBIO) have served as Guest Editors for Biogeosciences in 2013 and 2014 after the EUR-OCEANS Conference and the Liège Colloquium.

Within the MEECEproject (see website yy), the impacts of climatic change in the Benguela upwelling system have been assessed using a modeling platform (ROMS-BIOEBUS). Two simulation periods (1980-2000 and 2080-2100) have been run, forced by outputs from a low resolution global coupled ocean-atmosphere model (IPSL-CM4) with downscaling of the wind. Results for the future scenario show a mean increase in SST of 1.4°C over the Benguela domain, a decrease of 20 to 30 mmolO2.m-3 of the minimal oxygen concentrations in the northern Benguela, a decrease in planktonic biomass and primary production in the domain, except in the Northen Benguela region and close to the coast where the biological response is more complex.

A Remote Sensing project (Support To Science Element from ESA called Oceanflux-Theme Upwelling : http://due.esrin.esa.int/stse/projects/stse_project.php?id=160) covers these 2 EBUS from Peru and Benguela/Namibia. The goal here is to assess the sink or source role of these upwelling areas for GHG (CO2, N2O, CH4,…) using atmospheric and oceanic remotely sensed data together with a multiscale method of signal analysis (microcanonical formalism and multiplicative cascade). Presently an OST-ST EBUS-SOUTH project (2013-2016) (PIs: I. Dadou (DYNBIO), S. Illig (ECOLA)) aims to understand the relative contribution of the oceanic remote forcing of equatorial origin (Kelvin waves) versus the local forcing (wind, mesoscale activity) in the coupled physical/biogeochemical dynamics of these 2 EBUS in the Southern Hemisphere. For this we use altimetric data (T/P, Jason, AltiKa) simultaneously with other satellite data and coupled modelling. A PhD thesis is being co-supervised (DYNBIO-ECOLA) on the Benguela upwelling system.

The Transverse EBUS thematic has published 5 common papers (IF between 3 and 8) and as of today, 3 others are submitted with scientists from both ECOLA and DYNBIO teams.

Major scientific results

- Offshore Peru, the OMZ dynamics is very sensitive to the equatorial circulation and in particular to the transport of deoxygenated waters by the second Tsuchiya Jet, as shown in a regional coupled ROMS-BIOEBUS model. At the regional scale, variability in the rate of O2 change due to the ocean dynamics is one order of magnitude larger than the variability associated with the biogeochemical contribution. Close to the coast, where vertical mixing is enhanced and upwelling the most pronounced, the OMZ characteristics depend on the balance between physical and biogeochemical processes (Montes et al., 2014).

- Downscaling of the wind applied to the IPSL-CM4 low resolution global coupled ocean-atmosphere allows us to significantly improve the oceanic dynamics and the biogeochemical response of the Benguela upwelling in over the interannual period 1980-2000 in a coupled regional model. This wind downscaling is necessary for a proper simulation of the productive coastal upwelling and has an important impact on the nitrogen fueling from the coast to the inner oligotrophic gyre of the South East Atlantic (Machu et al., 2014).

B-Strategy for next 5 years

For the upcoming contract 2016-2020, scientists from ECOLA and DYNBIO teams collaborating on the EBUS Transverse Thematic topics have decided to merge in a single team SYSCO2 (Systèmes Complexes Couplés) naturally ending this Transverse Thematic. Planned future work on these topics is thus presented in the Prospective 2016-2010 of the SYSCO2 team.

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