48
S.M.P. Benbow
identify the variation in cloud, primary production and biomass of
zooplankton in order to demonstrate the possible variations in DMS.
Obviously, many more processes are involved, and this is an exercise
designed to indicate how future observations may contribute to future
work. The most readily available data were from maps prepared by the
USSR Ministry of Defense (Gorshkov, 1979), in the form of an oceanographic atlas. As well as being easily accessible and inexpensive, the
entire data set is in the same projection, at the same scale, and from the
same source, so reducing input error. The major areas of interest are the
impact of zooplankton grazing and the relationship of relative DMS
production to cloud cover.
Phytoplankton- Zooplankton Interactions
Zooplankton graze phytoplankton, and both phytoplankton, expressed as
the primary productivity, and zooplankton biomass are expressed as grams
carbon/metervday. Figure 3.2 shows the relative abundances of phytoplankton and zooplankton for the region according to mass of carboni
meter'; in most regions, as expected , there is a greater biomass of phytoplankton than zooplankton. In some regions, however, the biomass of
zooplankton can equal and in some cases exceed abundances of phytoplankton. It is in these areas where grazing stress upon phytoplankton is
likely to be highest. Cooper , Cooper, Saltzman, and Zika (1987) suggest
that DMS production is restricted to the photic zone of the oceans and
that the subsurface maximum of DMS concentration is a result of grazing
by zooplankton. Biomass of zooplankton can appear to exceed primary
productivity, as primary productivity is limited to the euphotic zone while
zooplankton graze throughout the water column.
Cloud Cover and DMS
Cloud cover is estimated from the available maps indicating the annual
average number of clear days (percentage of observations in which the
general cloud cover is from 0.0 to 0.3) and the annual average number of
cloudy days (percentage of observations in which the general cloud cover
is from 0.7 to 1.0). These were averaged to produce annual averages, as
shown in Figures 3.3 and 3.4. Figure 3.5, the relative clear and cloudy
days in the region, shows a gradual continuum of cloudiness from the
offshore to near coastal regions. The Gulf of Mexico was omitted during
operations to improve efficiency.
Figure 3.6 shows the combined regions of Figures 3.2 and 3.5 to
demonstrate that relative cloudiness coincides with relative biomasses of
zooplankton and phytoplankton. The number of cells for each class is
included in the legend, and it is immediately apparent that the greater
areas where phytoplankton exceed zooplankton are predominantly cloudy
(54% of the marine area). None of the regions where zooplankton exceed
S.M.P. Benbow
identify the variation in cloud, primary production and biomass of
zooplankton in order to demonstrate the possible variations in DMS.
Obviously, many more processes are involved, and this is an exercise
designed to indicate how future observations may contribute to future
work. The most readily available data were from maps prepared by the
USSR Ministry of Defense (Gorshkov, 1979), in the form of an oceanographic atlas. As well as being easily accessible and inexpensive, the
entire data set is in the same projection, at the same scale, and from the
same source, so reducing input error. The major areas of interest are the
impact of zooplankton grazing and the relationship of relative DMS
production to cloud cover.
Phytoplankton- Zooplankton Interactions
Zooplankton graze phytoplankton, and both phytoplankton, expressed as
the primary productivity, and zooplankton biomass are expressed as grams
carbon/metervday. Figure 3.2 shows the relative abundances of phytoplankton and zooplankton for the region according to mass of carboni
meter'; in most regions, as expected , there is a greater biomass of phytoplankton than zooplankton. In some regions, however, the biomass of
zooplankton can equal and in some cases exceed abundances of phytoplankton. It is in these areas where grazing stress upon phytoplankton is
likely to be highest. Cooper , Cooper, Saltzman, and Zika (1987) suggest
that DMS production is restricted to the photic zone of the oceans and
that the subsurface maximum of DMS concentration is a result of grazing
by zooplankton. Biomass of zooplankton can appear to exceed primary
productivity, as primary productivity is limited to the euphotic zone while
zooplankton graze throughout the water column.
Cloud Cover and DMS
Cloud cover is estimated from the available maps indicating the annual
average number of clear days (percentage of observations in which the
general cloud cover is from 0.0 to 0.3) and the annual average number of
cloudy days (percentage of observations in which the general cloud cover
is from 0.7 to 1.0). These were averaged to produce annual averages, as
shown in Figures 3.3 and 3.4. Figure 3.5, the relative clear and cloudy
days in the region, shows a gradual continuum of cloudiness from the
offshore to near coastal regions. The Gulf of Mexico was omitted during
operations to improve efficiency.
Figure 3.6 shows the combined regions of Figures 3.2 and 3.5 to
demonstrate that relative cloudiness coincides with relative biomasses of
zooplankton and phytoplankton. The number of cells for each class is
included in the legend, and it is immediately apparent that the greater
areas where phytoplankton exceed zooplankton are predominantly cloudy
(54% of the marine area). None of the regions where zooplankton exceed