1. PARTICULATE ORGANIC CARBON, LIGHT SCATTERING AND OCEAN COLOR Dariusz Stramski

2. OBJECTIVES
Develop an understanding of variability in the relationships between particulate organic carbon (POC), light scattering, and ocean color
Develop algorithms for estimating POC from optical measurements

3. BACKGROUND: reflectance Rrs , backscattering bp , and POC
Rrs ~ bb / a
bb ~ POC because
bulk bb is related to particle size-refractive index distributions F(D,n)
single particle organic carbon is related to particle size (D) and refractive index (n)
Therefore Rrs  bb  POC

4. EXAMPLE DATA FROM THE ROSS SEA AND ANTARCTIC POLAR FRONT ZONE
Rrs  bb bbp  POC
Note a significant difference for the POC vs bbp relationship between the two regions.
No such regional difference is seen in the bb vs Rrs relationship.

5. In situ measurements on the BIOSOPE cruise
Vertical profiling with Multisensor Datalogger System that includes:
Hydroscat-6 (HobiLabs) 442, 470, 555, 589, 620, and 671 nm
two a-Betas (HobiLabs) and 510 nm
two C-Stars (WetLabs) and 660 nm
fluorometer WetStar (WetLabs)
PAR sensor (Biospherical)
CTD sensors (Seabird)
The system is “autonomous” in the sense that all the sensors have internal power supply and data storage. The instruments can be deployed using any ship’s winch (there are no special requirements for the winch cable). If separate deployments are impossible then, as a minimum, it would be desirable to integrate Hydroscat-6 and two a-Betas with ship’s rosette or other in situ package to ensure that we have multispectral backscattering capability covering a broad spectral range.

6. Measurements on discrete water samples
Volume scattering function (l = 532 nm, 18 angles between 15o and 165o) with Dawn EOS (Wyatt Tech).
Because of limited experience, these measurements will have largely an exploratory character. The protocol will likely include the measurements on untreated and acid-treated samples to separate the contribution of PIC to light scatter. Relatively small volumes of water (~tens to hundreds of mL) will be required. These measurements will be made at selected stations and limited number of depths.
Elemental and mineralogical analyses of particulate matter with mass spectroscopy and X-ray techniques.
Water samples (~0.5 – 3 L) will be filtered and the sample filters will be stored for post-cruise analyses. These samples will be taken in parallel to samples for light scattering measurements. If water availability is problematic, then the dry weight filters could possibly be used after measuring the dry weight of particles.