PARTICULATE ORGANIC CARBON,
LIGHT SCATTERING AND OCEAN COLOR
Dariusz Stramski
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
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
EXAMPLE DATA FROM THE ROSS SEA
AND ANTARCTIC POLAR FRONT ZONE
Rrs  bb
bbp  POC
1000
0.012
Ross Sea
APFZ
POC [mg m-3]
bb (510) [m-1]
0.010
0.008
0.006
0.004
Ross Sea
APFZ
100
0.002
0.000
0.000
0.002
0.004
0.006
Rrs (555) [sr-1]
0.008
0.010
10
0.00001
0.0001
0.001
bbp (510) [m-1]
0.01
0.1
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) 420 and 510 nm
two C-Stars (WetLabs) 488 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.
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.