Absorption properties of marine particles and CDOM:

1
Absorption properties of marine particles and
CDOM

• Use of special measurement devices Ultrapath and
  PSICAM
• Marcel Babin
• Annick Bricaud
• Edouard Leymarie
• Antoine Sciandra

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Motivations (1)
- 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.

- 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.

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Motivations (2)

• - Some of our previous observations (aNAP/ap 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)
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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 study the variability of these contributions
in the various areas explored during the cruise
(contrasted wrt. iron limitation) -gt role
of iron in light absorption by NAP and CDOM?
- To extend our database of phytoplanktonic
absorption to ultra-oligotrophic waters, and
check the validity of the previously developed
parameterizations (af(l) vs. chl)
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Methods

• - Classical methods
• Particulate absorption concentration of
  particles on a GF/F filter, spectrophotometric
  analysis
• 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 gt 5 m)
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Ultrapath system
Peristaltic pump
Spectrophotometer TIDAS 1
Light source
Optical fiber
Ultrapath cell
Sample
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Ultrapath tests on natural samples and algal
cultures(DEA Maria Vlachou, 2003)
Phytoplanktonic culture
Dyfamed, 40 m

• Sensitive method for CDOM absorption
  measurements

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

• The rinsing protocol is being automatized to
  provide reproducible measurements (A. Sciandra,
  G. Malara)

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Methodological Development PSICAM (Point Source
Integrating Cavity Absorption Meter)

• Theoretical concept formulated by Elterman
  (1970), developed by Kirk (1995)
• Advantages
• Extremely sensitive (pathlengths up to more than
  10 meters)
• Insensitive to scattering by particles

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Agenda of the PSICAM development

• Dec 2003 Feb 2004 Development of a 3-D Monte
  Carlo code to optimize the design of the sphere
• Feb 2004 Visit to JTO Kirks lab
• March-April Building of the system
• May-June Tests in lab and calibration protocol
• July-October Tests at sea
• ? BIOSOPE

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Supplementary measurements needed

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

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Methodological Development PSICAM (Point Source
Integrating Cavity Absorption Meter)

• Theoretical concept formulated by Elterman
  (1970), developed by Kirk (1995)
• Advantages
• Extremely sensitive (pathlengths up to more than
  10 meters)
• Insensitive to scattering by particles

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SimulO Forward 3-D Monte-Carlo Simulation Program
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Surface / Volume properties

• Snell Fresnel Laws
• (example parallel plate)

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Simulation 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)

?
99 Lambertian surface