Absorption properties of marine particles and CDOM: Use of special measurement devices: Ultrapath and PSICAM Marcel Babin Annick Bricaud Edouard Leymarie Antoine Sciandra

Motivations (1) - In open ocean waters, especially in ultra-clear waters, these relative contributions are difficult to quantify and poorly known. We believe that these relative contributions are highly variable. We believe that these relative contributions are highly variable. - The relative contributions of CDOM, phytoplankton and non-algal particles (NAP) to light absorption have to be known for predicting/interpreting the inherent and apparent optical properties of the ocean.

Motivations (2) - Some of our previous observations ( a NAP / a p is largest in the Med Sea, and lowest in the Pacific, Bricaud et al. 1998) suggest that iron could contribute to non-algal absorption in some open ocean waters - Iron could also play a role in light absorption by CDOM (e.g. Emmenegger et al. 2001) (e.g. Emmenegger et al. 2001)

Objectives for the BIOSOPE cruise - To quantify the relative contributions of phytoplankton, CDOM and NAP to light absorption in the BIOSOPE area, using new (highly sensitive) measurement devices - To extend our database of phytoplanktonic absorption to ultra-oligotrophic waters, and check the validity of the previously developed parameterizations (a  ( ) vs. chl) - To study the variability of these contributions in the various areas explored during the cruise (contrasted wrt. iron limitation) -> role of iron in light absorption by NAP and CDOM? -> role of iron in light absorption by NAP and CDOM?

Methods - Classical methods: Particulate absorption: concentration of particles on a GF/F filter, spectrophotometric analysis Particulate absorption: concentration of particles on a GF/F filter, spectrophotometric analysis CDOM absorption: spectrophotometric measurements using 10 cm cells CDOM absorption: spectrophotometric measurements using 10 cm cells These methods are adequate for mesotrophic waters (will be used as often as possible as reference) but not for ultra- oligotrophic waters (CDOM absorption too low; large seawater volume needed for particulate absorption) two alternative (complementary) methods: - Ultrapath (commercial instrument, pathlength 2 m) - PSICAM (prototype in development, pathlength > 5 m)

Ultrapath cell Ultrapath system Light source Peristaltic pump Ultrapath cell Spectrophotometer TIDAS 1 2cm 200cm 10cm 50cm Optical fiber Sample

Ultrapath: tests on natural samples and algal cultures (DEA Maria Vlachou, 2003) Can be used also for particulate absorption measurements (needs accurate scattering correction –> ac-9) Phytoplanktonic culture Dyfamed, 40 m Sensitive method for CDOM absorption measurements The rinsing protocol is being automatized to provide reproducible measurements (A. Sciandra, G. Malara)

Methodological Development: PSICAM (Point Source Integrating Cavity Absorption Meter) Water sample Detector Inlet and outlet Monochromatic light source Spectralon sphere Theoretical concept formulated by Elterman (1970), developed by Kirk (1995)Theoretical concept formulated by Elterman (1970), developed by Kirk (1995) Advantages :Advantages : 1.Extremely sensitive (pathlengths up to more than 10 meters) 2.Insensitive to scattering by particles

Agenda of the PSICAM development Dec 2003 – Feb 2004 : Development of a 3-D Monte Carlo code to optimize the design of the sphere Dec 2003 – Feb 2004 : Development of a 3-D Monte Carlo code to optimize the design of the sphere Feb 2004 : Visit to JTO Kirk’s lab Feb 2004 : Visit to JTO Kirk’s lab March-April : Building of the system March-April : Building of the system May-June : Tests in lab and calibration protocol May-June : Tests in lab and calibration protocol July-October : Tests at sea July-October : Tests at sea  BIOSOPE  BIOSOPE

Supplementary measurements needed HPLC pigment concentrations HPLC pigment concentrations In situ absorption/ attenuation (ac-9) measurements (correction of Ultrapath a p measurements) In situ absorption/ attenuation (ac-9) measurements (correction of Ultrapath a p measurements) Particle dry weight (filtration of 7 L of seawater) Particle dry weight (filtration of 7 L of seawater) Iron concentration (particulate and dissolved), and ionic (ferric/ferrous) composition if possible Iron concentration (particulate and dissolved), and ionic (ferric/ferrous) composition if possible

Methodological Development: PSICAM (Point Source Integrating Cavity Absorption Meter) Water sample Detector Inlet and outlet Monochromatic light source Spectralon sphere Theoretical concept formulated by Elterman (1970), developed by Kirk (1995)Theoretical concept formulated by Elterman (1970), developed by Kirk (1995) Advantages :Advantages : 1.Extremely sensitive (pathlengths up to more than 10 meters) 2.Insensitive to scattering by particles

SimulO Forward 3-D Monte-Carlo Simulation Program Graph window to plot results in real time 2D picture to display current device projection. Simulation window to follow the calculation shell window to program different tasks

Surface / Volume properties Snell – Fresnel Laws : Snell – Fresnel Laws : (example : parallel plate) n=1 n=1.7 Parallel plate Photon Source Lambertian surface : (example : diffusion of a parallel beam) Various surface properties can be selected :Various surface properties can be selected : Reflection - Absorption : Photon Source Reflection Absorption Transparent, Absorption Diffusion with different choices of phase function Various Volume properties can be selected :Various Volume properties can be selected :

Simulation of the Point Source Water sample : a = 5 m -1, b = 2 m -1 (Petzold) Ideal and Simulated Sources ( Number of photons : )  99 % Lambertian surface 