340
distribution be determined. When dealing with mixed populations that exhibit a continuous
size distribution as in natural environments, bulk measurements cannot be interpreted in the
same way. The advent of individual measurements has created new ways of studying the
intersample and intrasample variability of particle absorption and fluorescence properties;
however, the gap between individual and bulk determination needs to be addressed in order
to assess the impact of environmental forcing on the variability of natural assemblages of cells
and other particulates in the ocean.
These informal talks and discussions centred on the problems and limitations of analyzing
marine particulates at the bulk and individual cell levels, providing a broad perspective of the
elements that must be considered for this type of analysis.
Consensus pivoted on the relevance of determining spectral absorption and possibly scattering,
because this type of determination is fundamental to understanding the propagation of
submarine light, including the fraction returned toward atmosphere ("ocean color" signature).
In addition, the spectral absorption in relation to pigment content and packaging is
fundamental to understanding the photophysiology of light adaptation and its subsequent effect
on the photosynthetic capabilities and the fluorescence signature of phytoplankton cells.
Because field samples are too dilute for direct spectrophotometric determinations, the most
common approach for characterizing the bulk absorption by oceanic particles has been the
concentration of samples on glass fiber filters. Such a sample filter is then scanned in a
spectrophotometer against a reference blank filter, and care must be taken to ensure a constant
reproducible water saturation of the filter before and after filtration. All agree that this
technique is, as yet, the most practical for field experiments. A high quality determination of
particulate absorption on a filter is a difficult task, however. The major concern of
investigators is the need to make a correction for the pathlength amplification effect fi (e.g.
Mitchell and Kiefer, 1984, 1988). The error associated with this correction may be large and
is one of the major sources of uncertainty in the derived values of absorption (Bricaud and
Stramski, 1990). The situation is complicated by the fact that the fi factor is dependent not
only on the amount of material retained on the filter (i.e. the optical density measured on the
filter), but also on the composition of particulate assemblage. Although the correction of fi has
distribution be determined. When dealing with mixed populations that exhibit a continuous
size distribution as in natural environments, bulk measurements cannot be interpreted in the
same way. The advent of individual measurements has created new ways of studying the
intersample and intrasample variability of particle absorption and fluorescence properties;
however, the gap between individual and bulk determination needs to be addressed in order
to assess the impact of environmental forcing on the variability of natural assemblages of cells
and other particulates in the ocean.
These informal talks and discussions centred on the problems and limitations of analyzing
marine particulates at the bulk and individual cell levels, providing a broad perspective of the
elements that must be considered for this type of analysis.
Consensus pivoted on the relevance of determining spectral absorption and possibly scattering,
because this type of determination is fundamental to understanding the propagation of
submarine light, including the fraction returned toward atmosphere ("ocean color" signature).
In addition, the spectral absorption in relation to pigment content and packaging is
fundamental to understanding the photophysiology of light adaptation and its subsequent effect
on the photosynthetic capabilities and the fluorescence signature of phytoplankton cells.
Because field samples are too dilute for direct spectrophotometric determinations, the most
common approach for characterizing the bulk absorption by oceanic particles has been the
concentration of samples on glass fiber filters. Such a sample filter is then scanned in a
spectrophotometer against a reference blank filter, and care must be taken to ensure a constant
reproducible water saturation of the filter before and after filtration. All agree that this
technique is, as yet, the most practical for field experiments. A high quality determination of
particulate absorption on a filter is a difficult task, however. The major concern of
investigators is the need to make a correction for the pathlength amplification effect fi (e.g.
Mitchell and Kiefer, 1984, 1988). The error associated with this correction may be large and
is one of the major sources of uncertainty in the derived values of absorption (Bricaud and
Stramski, 1990). The situation is complicated by the fact that the fi factor is dependent not
only on the amount of material retained on the filter (i.e. the optical density measured on the
filter), but also on the composition of particulate assemblage. Although the correction of fi has