Absorption properties of marine Absorption properties of marine particles and CDOM: particles and CDOM:

Use of special measurement devices: Use of special measurement devices: Ultrapath and PSICAMUltrapath and PSICAM

Marcel BabinMarcel Babin

Annick BricaudAnnick Bricaud

Edouard LeymarieEdouard Leymarie

Antoine SciandraAntoine Sciandra

Motivations (1)Motivations (1)

- In open ocean waters, especially - In open ocean waters, especially in ultra-clear in ultra-clear waters, these relative contributions are difficult to waters, these relative contributions are difficult to quantifyquantify and poorly known. and poorly known. We believe that these relative contributions We believe that these relative contributions are are highly variablehighly variable..

- The - The relative contributions of CDOM, relative contributions of CDOM, phytoplankton and non-algal particles (NAP) to light phytoplankton and non-algal particles (NAP) to light absorptionabsorption have to be knownhave to be known for for predicting/interpreting the inherent and apparent predicting/interpreting the inherent and apparent optical properties of the ocean.optical properties of the ocean.

Motivations (2)Motivations (2)

- - Some of our previous observations (Some of our previous observations (aaNAPNAP//aapp is largest is largest in the Med Sea, and lowest in the Pacific, Bricaud in the Med Sea, and lowest in the Pacific, Bricaud et al. 1998) suggest that et al. 1998) suggest that iron could contribute to iron could contribute to non-algal absorption in some open ocean watersnon-algal absorption in some open ocean waters

- Iron could also play a role in - Iron could also play a role in light absorption by light absorption by CDOMCDOM

(e.g. Emmenegger et al. 2001)(e.g. Emmenegger et al. 2001)

Objectives for the BIOSOPE cruiseObjectives for the BIOSOPE cruise

- To quantify the relative contributions of - To quantify the relative contributions of phytoplankton, CDOM and NAP to light phytoplankton, CDOM and NAP to light absorption in the BIOSOPE area, using new absorption in the BIOSOPE area, using new (highly sensitive) measurement devices(highly sensitive) measurement devices

- To extend our database of phytoplanktonic - To extend our database of phytoplanktonic absorption to ultra-oligotrophic waters, and check absorption to ultra-oligotrophic waters, and check the validity of the previously developed the validity of the previously developed parameterizations (aparameterizations (a(() vs. chl) ) vs. chl)

- To study the variability of these contributions in - To study the variability of these contributions in the various areas explored during the cruise the various areas explored during the cruise (contrasted wrt. iron limitation)(contrasted wrt. iron limitation)

-> role of iron in light absorption by NAP and -> role of iron in light absorption by NAP and CDOM? CDOM?

MethodsMethods

- - Classical methods:Classical methods:

• Particulate absorption: concentration of particles Particulate absorption: concentration of particles on a GF/F filter, spectrophotometric analysis on a GF/F filter, spectrophotometric analysis

• CDOM absorption: spectrophotometric CDOM absorption: spectrophotometric measurements using 10 cm cellsmeasurements 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 systemUltrapath system

Light source

Peristaltic pump

Ultrapath cell

Spectrophotometer TIDAS 1

2cm

200cm

10cm

50cm

Optical fiber

Sample

Ultrapath: tests on natural samples and algal culturesUltrapath: tests on natural samples and algal cultures(DEA Maria Vlachou, 2003)(DEA Maria Vlachou, 2003)

Hymenomonas elongata

l (nm)350 400 450 500 550 600 650 700 750

Co

effi

cien

t d

'ab

sorp

tio

n a

(m

-1)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

6,0

spectrophotomètreUltrapath

• Can be used also for particulate absorption measurements (needs accurate scattering correction –> ac-9)

Phytoplanktonic culture

(nm)

400 450 500 550 600 650 700

a (

44

0)

(m-1

)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

CDOMtotaleparticulaire

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: Methodological Development: PSICAM (Point PSICAM (Point Source Integrating Cavity Absorption Meter)Source Integrating Cavity Absorption Meter)

Water sample

Detector

Inlet and outlet

Monochromatic lightsource

Spectralon sphere

• Theoretical concept formulated by Elterman (1970), Theoretical concept formulated by Elterman (1970), developed by Kirk (1995)developed by Kirk (1995)

• Advantages :Advantages :1.1. Extremely sensitive (pathlengths up to more than 10 meters)Extremely sensitive (pathlengths up to more than 10 meters)2.2. Insensitive to scattering by particlesInsensitive to scattering by particles

Agenda of the PSICAM developmentAgenda of the PSICAM development

• Dec 2003 – Feb 2004 : Development of a 3-D Monte Dec 2003 – Feb 2004 : Development of a 3-D Monte Carlo code to optimize the design of the sphereCarlo code to optimize the design of the sphere

• Feb 2004 : Visit to JTO Kirk’s labFeb 2004 : Visit to JTO Kirk’s lab

• March-April : Building of the systemMarch-April : Building of the system

• May-June : Tests in lab and calibration protocolMay-June : Tests in lab and calibration protocol

• July-October : Tests at seaJuly-October : Tests at sea

BIOSOPEBIOSOPE

Supplementary measurements neededSupplementary measurements needed

• HPLC pigment concentrationsHPLC pigment concentrations

• In situ absorption/ attenuation (ac-9) In situ absorption/ attenuation (ac-9) measurements (correction of Ultrapath ameasurements (correction of Ultrapath app measurements) measurements)

• Particle dry weight (filtration of 7 L of seawater)Particle dry weight (filtration of 7 L of seawater)

• Iron concentration (particulate and dissolved), Iron concentration (particulate and dissolved), and ionic (ferric/ferrous) composition if possibleand ionic (ferric/ferrous) composition if possible

Methodological Development: Methodological Development: PSICAM (Point PSICAM (Point Source Integrating Cavity Absorption Meter)Source Integrating Cavity Absorption Meter)

Water sample

Detector

Inlet and outlet

Monochromatic lightsource

Spectralon sphere

• Theoretical concept formulated by Elterman (1970), Theoretical concept formulated by Elterman (1970), developed by Kirk (1995)developed by Kirk (1995)

• Advantages :Advantages :1.1. Extremely sensitive (pathlengths up to more than 10 meters)Extremely sensitive (pathlengths up to more than 10 meters)2.2. Insensitive to scattering by particlesInsensitive to scattering by particles

SimulOSimulO Forward 3-D Monte-Carlo Simulation Forward 3-D Monte-Carlo Simulation

ProgramProgramGraph 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 propertiesSurface / 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 Various surface properties can be selected :selected :

•Reflection - Absorption :Photon Source

Reflection Absorption

•Transparent, Absorption

•Diffusion with different choices of phase function

•Various Volume properties can be Various Volume properties can be selected :selected :

Simulation of the Point SourceSimulation of the Point Source

•Water sample : a = 5 m-1 , b = 2 m-1 (Petzold) •Ideal and Simulated Sources (Number of photons : 3.5

108)Simulated Irradiance on cavity wall

0.0035

0.004

0.0045

0.005

0.0055

0 45 90 135 180

Angle

Irra

dia

nc

e [A

.U]

Ideal Simulated

99 % Lambertian 99 % Lambertian surfacesurface