Oceanflux
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Oceanflux ESA Support to Science Element- Upwelling Theme |
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Objectives: Reconstruction of super-resolution oceanic pCO2 and air-sea CO2 fluxes at the air-sea interface in the Eastern Boundary Upwelling systems using remotely sensed product combinations either from the atmosphere or the ocean to properly assess the CO2 sources and sinks at small scales Tools: Development of a novel multiscale and non-linear method based on the Microcanonical Multifractal Formalism which takes into account the cascading properties of physical variables across the scales in complex signals Perspectives: To derive super resolution pCO2 from space from only remotely sensed observations so clearly the most obvious urgent requirement is to have in orbit another Thermal and Near-infrared Sensor for Carbon Observation which will deliver column abundances of atmospheric CO2 with a much denser sampling than GOSAT or SCIAMACHY (i.e. fixed flight pattern of GOSAT led to a very suboptimal sampling of the regions of interest). To extend our approach to infer DMS air-sea fluxes using EO derived phytoplankton functional types, CODiM (Comparison of Ocean Dimethylsulfide Models) type models, and DMSGO atlas. |
Scientific and societal issues
Understanding and quantifying ocean–atmosphere exchanges of the long-lived greenhouse gases (GHGs) such as carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) are important for understanding the global biogeochemical cycles of carbon and nitrogen in the context of ongoing global climate change. The global budgets of these gases are substantially determined by the marine system. Accurately predicting the evolution of the marine CO2 sink and the marine emissions of N2O and CH4 is of great importance for future climate change scenarios as used in studies for the Intergovernmental Panel on Climate Change (Denman et al., 2007).
The ocean can be thought of as a complex system in which a large number of different processes (physical, chemical, biological, atmosphere-ocean interactions, etc.) interact with each other at different spatial and temporal scales. These scales extend from millimeters to thousands of kilometers and from seconds to centuries (Dickey, 2003). In particular, there is a growing body of evidence that the upper few hundred meters of the oceans are dominated by submesoscale activity, covering the range 1-10 km, and that this activity is important to understand global ocean properties (Klein and Lapeyre, 2009). Accurately estimating the sources and sinks of the GHGs at the air-sea interface requires being able to resolve these small scales. However, the scarcity of oceanographic cruises and the lack of available satellite products for GHG concentrations at high resolution prevent from obtaining a global assessment of their spatial variability at small scales. For example, from the in situ ocean measurements the uncertainty of the net global ocean-atmosphere CO2 fluxes is between 20 and 30% (IOCCP, 2007), and could be higher in the Oxygen Minimum Zones (OMZ) of the Eastern Boundary Upwelling Systems (EBUS). This indeed suggests alternative approaches for inferring the CO2 fluxes at high resolution from remotely sensed data. In this project, we study the validity of a novel method to reconstruct maps of surface ocean partial pressure pCO2 and CO2 fluxes at super resolution (4 km) using sea surface temperature (SST) and ocean colour data at this resolution, and CarbonTracker CO2 fluxes data at low resolution (110 km). The responsible process for propagating the information between scales is related to cascading properties and multiscale organization, typical of fully developed turbulence. The methodology, based on the Microcanonical Multifractal Formalism, makes use, from the knowledge of singularity exponents, of the optimal wavelet for the determination of the energy injection mechanism between scales. We have applied such a methodology to the study of the Benguela Upwelling System.
General organization
The STSE project was led by Christoph Garbe and Véronique Garçon and articulated along 8 Work Packages including Collection of data, Boundary conditions for model, Estimation of k and pGHG, Resolution and adaptation, Assessment of high resolution, Validation and Comparison.
Partners
LEGOS (Toulouse), GEOSTAT/INRIA (Bordeaux), University of Heidelberg (Heidelberg, Germany), Karlsruhe Institute for Technology (Karlsruhe, Germany)
Financial support
The STSE from ESA granted for Oceanflux (SOLAS partnership) to LEGOS, GEOSTAT/INRIA University of Heidelberg and Karlsruhe Institute for Technology over the period 2011-2013 with an additional Change Contract Notice of 6 months.
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Results We performed the validation of our inferred high resolution oceanic pCO2 values with in situ observations from the QUIMA cruises (www.socat.info). An example over a cruise in July 2008 is shown below. While there are visible differences between the various reconstructions, the small scale patterns are nicely reproduced in the inferred pCO2 fields mimicking much better gradients and fronts present in the observed pCO2 transect than the CarbonTracker pCO2 field does.
Publications Hernandez-Carrasco I., Sudre J,. Garçon, V., Yahia H., Garbe, C., Paulmier A., Dewitte B., Illig, S., Dadou I. and Butz A. 2014, Reconstruction of ocean pCO2 and air-sea fluxes of CO2 from satellite imagery in the Benguela upwelling system, submitted. Garçon, V., Yahia H., Sudre J., Illig S., Hernandez-Carrasco I., Garbe, C., Dewitte ,B., Paulmier A., Montes, I., Dadou I. and Butz A.,2014, Super resolution validated maps of net GHG effect in the EBUS Oxygen Minimum Zone, submitted.
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To analyze the realism of the transition fronts a)Empirical PDFs for the singularity exponents of pCO2 fields from CarbonTracker and from the cascade of the remote sensing product combinations. b) Associated singularity spectra (all inferred pCO2 values in 2006 and 2008 have been used).
At low values of h (singularity exponent), related to the most singular manifold, the shape of the singularity spectrum for inferred data from merged products better matches a binomial cascade, with an improved description of the dimension of the sharpest transition fronts. We know from the theory that tracers advected by the flow in the turbulent regime, as it happens in the ocean, show a multifractal behavior with a characteristic singularity spectrum D(h) similar, for some type of turbulence, to D(h) for the binomial multiplicative process.
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