Development of ocean color algorithms in the Mediterranean Sea Rosalia Santoleri1,, Gianluca Volpe 1, Simone Colella1,3, Salvatore Marullo2, Maurizio Ribera D’Alcalà3, Vincenzo Vellucci3 1 2 ENEA -CR Casaccia – Sezione Modellistica Oceanografica 3 Stazione Zoolologica ‘A. Dohrn’ Laboratorio di Oceanografia Biologica

ISAC Contribution to Ocean Color activity Mediterranean high resolution surface chlorophyll mapping Use available bio-optical data sets to estimate the uncertainties of the existing ocean colour algorithms and to define an optimal chlorophyll algorithm for the Mediterranean Sea. Adapt the OC processing software to include selected regional algorithms and validate satellite chlorophyll estimates on the basis of in situ data. Evaluate the uncertainties of all current global satellite chlorophyll products available from public archive (e.g. DAAC) in the Mediterranean Reprocessing SeaWiFS dataset using the selected Mediterranean algorithm Prepare Mediterranean gridded data compatible with model requirements.

Why Mediterranean needs regional algorithm ? Chlorophyll concentrations over the oligotrophic waters of the Mediterranean Sea are systematically overestimated when global algorithms (e.g. OC4v4) are used to convert blue-to-green reflectance ratios in to chlorophyll-a concentrations: Gitelson et al. (Journal of Marine System, 1996) D’Ortenzio et al. (SIMBIOS meeting January 2001) D’Ortenzio et al. (Remote sensing of the Environment, 2002) Bricaud et al . (Remote sensing of the Environment, 2002) Claustre et al. (Geoph. Res. Letters, 2002) From these works it results that global algorithms cannot be applied to-court to the Mediterranean Sea but a specific cal/val activity is needed.

Mediterranean Ocean Color CAL/VAL DATA SETS 10 Mediterranean cruises from 1998 up to now were organized by ISAC in the framework of Italian National Projects Bio-optical stations Bio-optical measurements: (143 chl/opt measurement points) to define the Mediterranean regional algorithm In water downwelling irradiance and upwelling radiance profiles using SATLANTIC SPMR above water measurements using the SIMBAD and SIMBADA radiometer In the bio-optical stations phytoplankton pigments distribution (HPLC and spectro-fluorometric analysis) and ancillary biological data were also acquired following NASA protocols. In situ chlorophyll-a data: (872 chl profiles) to validate SeaWiFS, Polder, MODIS, MERIS chlorophyll products and merged level 3 binned data produced by Mersea

Cruise Period Zone # of profiles Chlorophyll Range Satlantic SIMBAD(A)   MIN MAX MATER 4 25/4/1998 15/5/1998 Sardinia Channel Sicily Channel 57 0.025 0.105 - MATER 5 20/10/1998 27/10/1998 50 0.047 0.085 EMTEC 99 20/4/1999 7/5/1999 Ionian Sea 125 0.039 0.137 20 MATER 6 14/5/1999 30/5/1999 100 0.003 0.135 PROSOPE 04/09/1999 14/10/1999 Western Basin 16 0.020 0.112 SYMPLEX 99 21/10/1999 6/11/1999 212 0.176 12 NORBAL 1 26/3/2000 19/4/2000 Gulf of Lions 81 0.113 2.289 NORBAL 2 5/12/2001 20/12/2001 Tyrrhenian Sea 65 0.088 0.386 13 14 NORBAL 4 6/3/2003 26/3/2003 115 0.428 7.061 28 NORBAL 5 18/4/2003 25/4/2003 40 0.605 2.096 4 7 DINA* 29/3/2001 28/8/2001 Gulf of Naples 11 0.079 0.455 DYFAMED* 5/2/1998 25/11/2002 Liguro-Provencal 55 0.042 2.366 All cruises 1998-2003 Mediterranean 872 92 49 141

In situ chlorophyll-a profiles and optical measurements (143 stations) were performed during several cruises carried out in the Mediterranean Sea through the years 1998-2003 on board the R/V Urania of the National Research Council (CNR). SIMBIOS data taken during PROSOPE cruise were also included Satellite geophysical parameter retrieval and validation

Validation of Ocean Color Algorithms REGIONAL Validation of Ocean Color Algorithms OC4v4: R is log10 of either the 443/555 or the 490/555 or the 510/555 band reflectance ratios, depending on its value (the maximum is chosen) D’Ortenzio et al. 2002 (DORMA): R is log10 of the 490/555 band reflectance ratios. Bricaud et al. 2002: R is log10 of the 443/555 band reflectance ratios for Chl<0.2 (OC4v4 is used in the other cases) GLOBAL

NEW MEDITERRANEAN ALGORITHM MEDOC4 : R is log10 of either the 443/560 or the 490/555 or the 510/555 band reflectance ratios. The switch from one band ratio to another one is based on the chlorophyll concentration itself (the Maximum is Chosen)

SeaWiFS data validation A Match-up dataset between concurrent SeaWiFS data and in situ measurements has been contructed SeaWiFS L1A passes corresponding to in situ observation were selected The regional algorithms (DORMA, Bricout et al, and the new MED OC4) were inserted in the SeaDAS Code SeaWiFS L1A passes were processed using the different algorithms A Match-up dataset is contructed.

Map of the Satellite-in situ match-up stations

Merging OC data in the MED Define the error of global OC color products at regional scale and define a strategy to take into account the regional optical properties of the MED Define of the suitable intercalibration and merging tecnique for OC Define an optimal interpolation algorithm that takes in to account the different characteristics of ocean colour retrieval in case I/case II waters.

10 March 2003

12 March 2003

25 March 2003

Primary production in the Mediterranean Sea from remote sensing data: a model adaptation

Depth (m) CHL (mg m-3) Depth (m) CHL (mg m-3)

Remote Sensed data of pigment concentration Trophic States e Morel and Berthon’s (1989) Correlations Primary Production Maps

Antoine et al.,1995 Bosc et al.,2003 In situ C14 Method WEST MED: 197 gc m-2 y-1 EST MED: 137 gc m-2 y-1 WEST MED: 172 gc m-2 y-1 EST MED: 123 gc m-2 y-1 Bosc et al.,2003 In situ C14 Method EST MED: 55-97 gc m-2 y-1 WEST MED: 78-150 gc m-2 y-1

Chlorophyll vertical distribution in first two trophic states Morel (dashed line) This work (continuous line)

Chlorophyll concentration intervals: 4000 chlorophyll profiles acquired in the Mediterranean Sea during 16 cruises (1996-up to now) has been use to compute the chlorophyll concetration of the of the first optical depth (Cpd) Chlorophyll concentration intervals: >0.05, 0.05-0.1, 0.1-0.15, 0.15-0.3, 0.3-0.45, 0.45-1.5, 1.5-5, > 5 mg m-3

Morel (dashed line) This work (continuous line)

= ≠ Ctot=40.6 Cpd0.46 Ctot=40.6 Csat0.459 Ctot=54.679 Cpd0.6532

gc m-2 g-1 Gennaio Febbraio Marzo Aprile Maggio Giugno Luglio Agosto Settembre Ottobre Novembre Dicembre 0.2 0.4 0.6 0.8 1.0 1.2 1.4 gc m-2 g-1 1.6

Antoine et al.,1995 Bosc et al.,2003 In situ C14 method Our Estimate WEST MED: 197 gc m-2 y-1 EST MED: 137 gc m-2 y-1 WEST MED: 172 gc m-2 y-1 EST MED: 123 gc m-2 y-1 Bosc et al.,2003 In situ C14 method EST MED: 55-97 gc m-2 y-1 WEST MED: 78-150 gc m-2 y-1 Our Estimate WEST MED: 130 gc m-2 y-1 EST MED: 95 gc m-2 y-1