107
1981). Profiles of diffuse downwelling light attenuation, K, exhibited classical
exponential decreases with depth although we always recorded relatively higher values
of K in the water layers from 0 to 5 or 10 m. This phenomenon was probably not due
to greater pigment attenuation but was mainly the result of the large changes in the
spectrum of light energy which occur near the surface (see Jewson et ~. 1984).
Although plant pigments are only partly responsible for the light attenuation in
the sea, both Secchi depths and K were significantly correlated with the chlorophyll
concentrations down to about 37% (Table 2). The regression of chlorophyll on Secchi
depths was the most significant (0.1% level). We suggest that further investigation
may show that Secchi measurements can be extremely useful in this region for providing
rapid estimations of nearsurface chlorophyll and light attenuation which are required
to validate data acquired by remote sensing.
The Secchi depths and the values of the diffuse downwelling coefficients in the
pelagic waters were typical for oligotrophic seas. It should be noted however that
neither the Secchi depth values nor those of the attenuation coefficients reflect
the contribution of deep chlorophyll maxima to the total areal standing crop of this
pigment.
eh I orophy 11
The areal concentrations of chlorophyll in the euphotic zone ranged from 3.1 to
18.0 mg.m- 2 (Fig. 2). Note that while the average chlorophyll concentration (mg.m- 3 )
at pelagic stations (>80 m) was much lower than that at neritic sites (.:80 m) the
total chlorophyll standing stocks (mg.m- 2 ) in the former locations were frequently
greater. The lowest areal chlorophyll concentrations for neritic waters were observed in AID-4 (July 1981).
At all seasons, both for nearshore and pelagic waters; the majority of the chlorophyll was associated with organisms smaller than 3 ~m (Fig. 3). However there was
no apparent trend to greater proportions of picoplankton with depth (Fig. 4), as has
been reported elsewhere (Li et ~. 1983).
For all pelagic stations of cruises AID-1 through 4, we observed deep chlorophyll
maxima at depths from 75 to 150 m (Fig. 5). The two 'deep' stations measured in
AID-5 (5-2, 5-3) were exceptions to this. In future work it will be of importance
to investigate whether these deep chlorophyll maxima are in any way seasonal phenomena.
As yet we have not completed the interpretation of the in vivo fluorometric surface
scans from all cruises. During AID-l a sharp front was observed both in chlorophyll
and surface temperatures between the nearshore and pelagic waters. On other cruises
(e.g. AID-5) the surface front was absent although in general a gradient from higher
to lower surface chlorophyll was recorded over the first 20 kms as the vessel steamed
west from the shore.
1981). Profiles of diffuse downwelling light attenuation, K, exhibited classical
exponential decreases with depth although we always recorded relatively higher values
of K in the water layers from 0 to 5 or 10 m. This phenomenon was probably not due
to greater pigment attenuation but was mainly the result of the large changes in the
spectrum of light energy which occur near the surface (see Jewson et ~. 1984).
Although plant pigments are only partly responsible for the light attenuation in
the sea, both Secchi depths and K were significantly correlated with the chlorophyll
concentrations down to about 37% (Table 2). The regression of chlorophyll on Secchi
depths was the most significant (0.1% level). We suggest that further investigation
may show that Secchi measurements can be extremely useful in this region for providing
rapid estimations of nearsurface chlorophyll and light attenuation which are required
to validate data acquired by remote sensing.
The Secchi depths and the values of the diffuse downwelling coefficients in the
pelagic waters were typical for oligotrophic seas. It should be noted however that
neither the Secchi depth values nor those of the attenuation coefficients reflect
the contribution of deep chlorophyll maxima to the total areal standing crop of this
pigment.
eh I orophy 11
The areal concentrations of chlorophyll in the euphotic zone ranged from 3.1 to
18.0 mg.m- 2 (Fig. 2). Note that while the average chlorophyll concentration (mg.m- 3 )
at pelagic stations (>80 m) was much lower than that at neritic sites (.:80 m) the
total chlorophyll standing stocks (mg.m- 2 ) in the former locations were frequently
greater. The lowest areal chlorophyll concentrations for neritic waters were observed in AID-4 (July 1981).
At all seasons, both for nearshore and pelagic waters; the majority of the chlorophyll was associated with organisms smaller than 3 ~m (Fig. 3). However there was
no apparent trend to greater proportions of picoplankton with depth (Fig. 4), as has
been reported elsewhere (Li et ~. 1983).
For all pelagic stations of cruises AID-1 through 4, we observed deep chlorophyll
maxima at depths from 75 to 150 m (Fig. 5). The two 'deep' stations measured in
AID-5 (5-2, 5-3) were exceptions to this. In future work it will be of importance
to investigate whether these deep chlorophyll maxima are in any way seasonal phenomena.
As yet we have not completed the interpretation of the in vivo fluorometric surface
scans from all cruises. During AID-l a sharp front was observed both in chlorophyll
and surface temperatures between the nearshore and pelagic waters. On other cruises
(e.g. AID-5) the surface front was absent although in general a gradient from higher
to lower surface chlorophyll was recorded over the first 20 kms as the vessel steamed
west from the shore.