water reflectance, particularly from resuspension of carbonate sediments during stormy
periods and the mass appearance of coccoliths during the declining stages of
coccolithoporid blooms (Brown and Yoder, 1994) and extensive “whiting” conditions
in inland lakes and coastal and offshore waters.
2. Chlorophyll as an Integrative Bioindicator
Chl a is the dominant light harvesting pigment and is universally present
in eukaryotic algae and the Cyanophyceae (cyanobacteria or “bluegreen algae”)
(Rowan, 1989). The only potential water column phototrophs lacking chl a are
certain photosynthetic bacteria such as Purple or Green bacteria, which
contain bacteriochlorophylls with different absorption maxima, and phototrophic
Archaebacteria containing bacteriorhodopsin as the light-harvesting pigment.
Chl a is commonly measured in water quality monitoring programs for coastal and
inland waters (Jordan et al., 1991; Morrow et al., 2000;, Cracknell et al., 2001;, Casazza
et al., 2003), in surveillance programs for harmful algal blooms (Munday and Zubkoff;
Paerl, 1988; Richardson, 1996; Kahru and Mitchell, 1998;, Pettersson et al., 2000), and
in ecological studies of phytoplankton biomass and productivity (Cole and Cloern,
1987; Talling, 1993;, Gallegos and Jordan, 2002; Lefevre et al., 2003). The contribution
of phytoplankton derived primary production on continental margins (shelves, slopes,
and rises) to both global ocean production and particulate organic carbon export to the
deep oceans has been underexamined, but appears to be highly significant (Walsh,
1991; Jahnke, 1996).
It is important to keep in perspective that remote measurements of in situ
phytoplankton using passive solar reflectance are generally incapable of isolating the
chlorophyll signal from other cell components and other optically active compounds
(OACs) in the water column. Even the chlorophyll fluorescence signals detected by
active LIDAR systems can be affected by other fluorescing materials, red reabsorption
by chl a and optical processes of the extracellular environment (Doerffer, 1993;
Pozdnyakov et al., 2002). Chl a is packaged with other pigments within the refractive
and reflective contents of algal cell walls, membranes, and other cytoplasm
constituents. An extensive analysis (n ~ 5600 stations) of ocean pigment data found an
average total pigment to chl a ratio of 2.164, with a range of 1.876 to 2.876 across
cruises and ocean provinces (Aiken et al., 1995).
Uniform sphere models of cells are unable to reasonably describe scattering in
marine phytoplankton cells (Quinby-Hunt et al., 1989). A three layered model using a
high refraction index for the outer layer (cell wall component) and low indices for
middle (chloroplasts) and inner (cytoplasm) layers performed well in simulating a
mixed particle size distribution from the central Pacific gyre (Kitchen and Zaneveld,
1992). Non-extractive, remote sensing schemes to detect and monitor phytoplankton
chlorophyll must contend with the complex scattering and absorbing features of this
total cell package. In most natural assemblages, cell populations of mixed species with
variable shapes and sizes (submicron to tens of microns or more) and differing cell wall
constituents and pigment suites occur in spatially heterogeneous patterns. Other
photosynthetic and photoprotective pigments have overlapping spectral absorption with
chl a, especially at the blue, Soret band of chlorophyll (Figure 1). An example of an
aggregate absorption spectrum (chl a plus accessory chlorophylls and carotenoids) is
compared to an isolated chl a spectrum in Figure 2. The data in Figure 2 were produced
using the specific absorption coefficients of Bidigare et al. (1990; see Figure 1) and a
29
Optical Remote Sensing Techniques
periods and the mass appearance of coccoliths during the declining stages of
coccolithoporid blooms (Brown and Yoder, 1994) and extensive “whiting” conditions
in inland lakes and coastal and offshore waters.
2. Chlorophyll as an Integrative Bioindicator
Chl a is the dominant light harvesting pigment and is universally present
in eukaryotic algae and the Cyanophyceae (cyanobacteria or “bluegreen algae”)
(Rowan, 1989). The only potential water column phototrophs lacking chl a are
certain photosynthetic bacteria such as Purple or Green bacteria, which
contain bacteriochlorophylls with different absorption maxima, and phototrophic
Archaebacteria containing bacteriorhodopsin as the light-harvesting pigment.
Chl a is commonly measured in water quality monitoring programs for coastal and
inland waters (Jordan et al., 1991; Morrow et al., 2000;, Cracknell et al., 2001;, Casazza
et al., 2003), in surveillance programs for harmful algal blooms (Munday and Zubkoff;
Paerl, 1988; Richardson, 1996; Kahru and Mitchell, 1998;, Pettersson et al., 2000), and
in ecological studies of phytoplankton biomass and productivity (Cole and Cloern,
1987; Talling, 1993;, Gallegos and Jordan, 2002; Lefevre et al., 2003). The contribution
of phytoplankton derived primary production on continental margins (shelves, slopes,
and rises) to both global ocean production and particulate organic carbon export to the
deep oceans has been underexamined, but appears to be highly significant (Walsh,
1991; Jahnke, 1996).
It is important to keep in perspective that remote measurements of in situ
phytoplankton using passive solar reflectance are generally incapable of isolating the
chlorophyll signal from other cell components and other optically active compounds
(OACs) in the water column. Even the chlorophyll fluorescence signals detected by
active LIDAR systems can be affected by other fluorescing materials, red reabsorption
by chl a and optical processes of the extracellular environment (Doerffer, 1993;
Pozdnyakov et al., 2002). Chl a is packaged with other pigments within the refractive
and reflective contents of algal cell walls, membranes, and other cytoplasm
constituents. An extensive analysis (n ~ 5600 stations) of ocean pigment data found an
average total pigment to chl a ratio of 2.164, with a range of 1.876 to 2.876 across
cruises and ocean provinces (Aiken et al., 1995).
Uniform sphere models of cells are unable to reasonably describe scattering in
marine phytoplankton cells (Quinby-Hunt et al., 1989). A three layered model using a
high refraction index for the outer layer (cell wall component) and low indices for
middle (chloroplasts) and inner (cytoplasm) layers performed well in simulating a
mixed particle size distribution from the central Pacific gyre (Kitchen and Zaneveld,
1992). Non-extractive, remote sensing schemes to detect and monitor phytoplankton
chlorophyll must contend with the complex scattering and absorbing features of this
total cell package. In most natural assemblages, cell populations of mixed species with
variable shapes and sizes (submicron to tens of microns or more) and differing cell wall
constituents and pigment suites occur in spatially heterogeneous patterns. Other
photosynthetic and photoprotective pigments have overlapping spectral absorption with
chl a, especially at the blue, Soret band of chlorophyll (Figure 1). An example of an
aggregate absorption spectrum (chl a plus accessory chlorophylls and carotenoids) is
compared to an isolated chl a spectrum in Figure 2. The data in Figure 2 were produced
using the specific absorption coefficients of Bidigare et al. (1990; see Figure 1) and a
29
Optical Remote Sensing Techniques