Showing papers by "David Antoine published in 2009"

Climate-Driven Basin-Scale Decadal Oscillations of Oceanic Phytoplankton

Abstract: Phytoplankton--the microalgae that populate the upper lit layers of the ocean--fuel the oceanic food web and affect oceanic and atmospheric carbon dioxide levels through photosynthetic carbon fixation. Here, we show that multidecadal changes in global phytoplankton abundances are related to basin-scale oscillations of the physical ocean, specifically the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation. This relationship is revealed in approximately 20 years of satellite observations of chlorophyll and sea surface temperature. Interaction between the main pycnocline and the upper ocean seasonal mixed layer is one mechanism behind this correlation. Our findings provide a context for the interpretation of contemporary changes in global phytoplankton and should improve predictions of their future evolution with climate change.

Field characterization of wave‐induced underwater light field fluctuations

Abstract: for wave heights of � 0.5 m or wind speeds between � 1 and 5 m s � 1 . Fluctuations are reduced under clear skies for wave heights >� 1.5 m or for wind speeds >7 m s � 1 . The dominant periods of the fluctuations in the upward flux are changing in parallel to those in the downward flux. The amplitude of the fluctuations in the upward flux is, however, evolving in the opposite direction as compared to the downward flux, e.g., decreasing when the water becomes clearer.

GlobColour - the European Service for Ocean Colour

Abstract: The GlobColour project has been initiated and funded by the ESA Data User Element Programme to develop a satellite based ocean colour data service to support global carbon-cycle research and operational oceanography. It aims to satisfy the scientific requirement for a long (10+ year) time-series of consistently calibrated global ocean colour information with the best possible spatial coverage. In order to cover the long time span necessary for climate monitoring purposes, the required ocean colour data set can only be built by merging together observations made with different satellite systems. To that purpose, MERIS products are merged with MODIS and SeaWiFS and a Full Data Set (FPS) covering more than 10 years of observation has been built and made available to the scientific community (www.globcolour.info ) and in particular to the key users of the project: IOCCP, IOCCG and UKMO. Prior to the delivery, a very thorough calibration and validation exercise covering the entire spatial and temporal extent of the data set has been performed. This exercise provided a deep understanding of the different input data streams, and led to the prototyping of three different merging methods: simple averaging, error-weighted averaging and an advanced retrieval based on fitting an in-water bio-optical model to the merged set of observed normalised water-leaving radiances (nLw’s). This third technique is also being utilised by the NASA Ocean Color Time-Series Project, and is termed GSM because it originates from the Garver et al. (1997) bio-optical model (Maritorena & Siegel, 2005). Error statistics from the initial sensor characterisation are also used as an input to both the weighted averaging and GSM merging methods, and propagate through the merging process to provide error estimates on the output merged products. These error estimates are a key component of GlobColour as they are invaluable to the users; particularly the modellers who need them in order to assimilate the ocean colour data into their ocean simulations. The service is distributing global data sets of chlorophyll-a concentration, normalised water-leaving radiances, diffuse attenuation coefficient, coloured dissolved and detrital organic materials, total suspended matter or particulate backscattering coefficient, turbidity index, cloud fraction and quality indicators. New demonstration products are available online too: Photosynthetic Available Radiation, Depth of the Heated Layer, Secchi Disk Depth. 1. DEVELOPMENT OF THE PROJECT The three year project was kicked-off in November 2005 under the leadership of ACRI-ST (France). The objective is to produce a global daily ocean colour data set with the best possible coverage by merging together data from the three most capable sensors: SeaWiFS on GeoEye’s Orbview-2 mission, MODIS on NASA’s Aqua mission and MERIS on ESA’s ENVISAT mission. In setting up the GlobColour project, three user organisations were invited to help. Their roles are to specify the detailed user requirements, act as a channel to the broader end user community and to provide feedback and assessment of the results. The International Ocean Carbon Coordination Project (IOCCP) based at UNESCO in Paris provides direct access to the carbon cycle modelling community's requirements and to the modellers themselves who will use the final products. The UK Met Office's National Centre for Ocean Forecasting (NCOF) in Exeter, UK, provides an understanding of the requirements of oceanography users, and the IOCCG bring their understanding of the global user needs and valuable advice on best practice within the ocean colour science community. The first year was a feasibility demonstration phase that was successfully concluded at a user consultation workshop organised by the Laboratoire d'Océanographie de Villefranche, France, in December 2006. Error statistics and inter-sensor biases were quantified by comparison with in-situ measurements from moored optical buoys and ship based campaigns, and used as input to the merging. The second year was dedicated to the production of the time series. In total more than 25 Tb of input (level 2) data have been ingested and 14 Tb of intermediate and output products created, with 4 Tb of data distributed to the user community. Quality control (QC) is provided through the Diagnostic Data Sets (DDS), which are extracted sub-areas covering locations of idata collection or interesting oceanographic phenomena. The Full Product Set (FPS) covers global daily merged ocean colour products in the time period 1997-2008 and is freely available for use by the worldwide science community at http://hermes.acri.fr/. The GlobColour service distributes global daily, 8-day and monthly data sets at 4.6 km resolution for, chlorophyll-a concentration, normalised water-leaving radiances (412, 443, 490, 510, 531, 555 and 620 nm, 670, 681 and 709 nm), diffuse attenuation coefficient, coloured dissolved and detrital organic materials, total suspended matter or particulate backscattering coefficient, turbidity index, cloud fraction and quality indicators. Error statistics from the initial sensor characterisation are used as an input to the merging methods and propagate through the merging process to provide error estimates on the output merged products. These error estimates are a key component of GlobColour as they are invaluable to the users; particularly the modellers who need them in order to assimilate the ocean colour data into ocean simulations. See the Product User Guide (PUG) for further details on the GlobColour products http://www.globcolour.info/CDR_Docs/GlobCOLOUR_PUG.pdf. An intensive phase of validation has been undertaken to assess the quality of the data set. In addition, inter-comparisons between the different merged datasets will help in further refining the techniques used. Both the final products and the quality assessment were presented at a second user consultation in Oslo on 20-22 November 2007; presentations are available on the GlobColour WWW site (www.globcolour.info). The NRT service was started mid-2008, with a global daily delivery of merged MERIS and MODIS ocean colour data to primarily support operational oceanography. From spring 2009, the GlobColour service will feed into the European Community funded Marine Core Service, MyOcean, which starts to provide, in 2009, a suite of services to support Europe's decision makers. GlobColour's merged ocean colour dataset are provided from April 2009 by the Global Ocean Colour Thematic Assembly Centre (OC G-TAC) whose main objective is to bridge the gap between space agencies providing ocean colour data and GMES marine applications.

Satellite-driven modeling of the upper ocean mixed layer and air-sea co2 flux in the Mediterranean Sea

Abstract: Abstract The air–sea CO 2 flux, the carbon export to the deep layers, and more generally the carbon budgets are presently poorly characterized in the Mediterranean Sea. An approach to the simulation of these fluxes at regional scale is proposed, based on an array of unconnected one-dimensional (1D) physical–biological–chemical coupled models. The rationale is to massively assimilate satellite information, on one hand to derive accurate surface heat fluxes, and, on the other hand, to implicitly account for the horizontal processes not explicitly represented in the 1D scheme. This method is applied here to simulate the upper ocean physical and biogeochemical dynamics of the entire Mediterranean Sea over the years 1998–2004, and at a 0.5° spatial resolution. The mixed-layer annual cycles are validated against the values determined from a database of in situ temperature profiles, demonstrating the validity of the approach in various physical regimes. A validation of the simulated annual cycles of the total inorganic carbon (TCO 2 ) and of the carbon dioxide partial pressure ( p CO 2 ) is presented at a measurement site in the northwestern Mediterranean where both properties were determined in 1998–1999 and in 2003–2004. An additional validation of the p CO 2 fields is presented using along-track data collected during the “Productivite des Systemes Oceaniques Pelagiques” (PROSOPE) cruise. The basin-scale air–sea carbon budget derived from the model outputs shows that the Mediterranean Sea, over the study period, is close to equilibrium with the atmosphere, with a slight sink for the atmospheric CO 2 . This is in agreement with the results previously obtained via indirect methods and is supported here by a series of sensitivity studies. A detailed analysis of the p CO 2 and TCO 2 seasonal distributions in the Mediterranean Sea is provided for the first time. It shows that the biological processes play a major role in shaping the p CO 2 seasonal evolution in the eastern and western basins.

The MERIS water products: Performance, current issues and potential future improvements

Abstract: MERIS Level 1 and Level 2 water products will be improved in the 3rd MERIS reprocessing which is planned to take place before the end of 2009. The instrument radiometric degradation model will be updated. Improvements to the atmospheric correction in both case 1 and case 2 waters will be implemented. A vicarious adjustment strategy to remove residual biases in the Level 2 marine signals will be put in place. In addition, a cloud screening scheme with improved detection capabilities will improve the cirrus detection capability. In parallel, long term algorithmic improvements are being pursued and are partially covered by three exploratory ongoing studies. The first study addresses the limitation of the current MERIS atmospheric correction scheme in sun glint conditions. The second aims at defining an operational adjacency effect correction. The third study makes use of the ability of MERIS to measure transmission in the O 2 -A oxygen band to better identify and characterize clouds and aerosols.