5
and Sakshaug 1983).
Except for situations with dense phytoplankton blooms and local
turbidity from melting glacial ice, polar waters are blue and rather
transparent. Hart (1962) and ACDA cruise data (Holm-Hansen and Chapman
1983) indicate a maximum Secchi depth of about 40m in Antarctic waters,
which corresponds well with a maximum estimate of about 100m for the
1% photon flux density (PFD) in that area (Slawyk 1979).
In the Arctic
and adjacent seas the estimate for the maximum 1% PFD level is SO-60m;
during blooms this decreases to 20-30m (Ellertsen et al. 1981, Sakshaug
et al. 1981, Platt et al. 1982).
SPATIAL AND SEASONAL DISTRIBUTION OF. POLAR PHYTOPLANKTON
In spite of half a century of studies in the Antarctic, the spatial
and temporal distribution of phytoplankton is not well documented. There
are several reasons for this. First, distances are vast, the seas are
often rough, and expeditions are relatively few and very expensive. Second, the most extensive studies were done by the early researchers
(Hart 1934, 1942, Hentschel 1932), but they generally examined only
net tow samples and so included only the relatively large cells. Third,
the numerous cruises of the past 20 years have been concentrated in a
few geographical ar"eas and have generally taken place during the austral
summer period (see review by El-Sayed 1984). Some of the more valuable
quantitative data on species distributions have been obtained by the
inverted microscope method (e.g. Hasle 1969), but these studies have
been relatively few and restricted in scope. The following generalizationsemerge from all these studies.
(1) There is a richness of phytoplankton around South Georgia, with both a spring and an autumn bloom,
and the Scotia Sea also appears richer than other areas. There is,
however, a delay of the spring bloom with increasing latitude due to
light and ice effects. The "Northern Region" (Polar Front to 330 n.m.
south of it) with generally open waters exhibits a peak in early December; the "Intermediate Region" and the Scotia" Sea in January; and the
"Southern Region" (south of the Antarctic Circle) exhibits a peak in
mid-late February.
(2) The main picture from December and onwards will
consequently be one of poverty of phytoplankton in all offshore waters.
Chlorophyll is generally in the range of 0.1 to 0.3 ~g per liter (e.g.
El-Sayed 1970b).
(3) Phytoplankton blooms (>1.5 ~g chl. per liter) are
characteristic of shelf areas (300 to SOOm depth) in the Ross and Weddell Seas, around the Antarctic Peninsula, in waters over the Scotia
Ridge, and at times along receding ice egdes. Blooms in these waters
and Sakshaug 1983).
Except for situations with dense phytoplankton blooms and local
turbidity from melting glacial ice, polar waters are blue and rather
transparent. Hart (1962) and ACDA cruise data (Holm-Hansen and Chapman
1983) indicate a maximum Secchi depth of about 40m in Antarctic waters,
which corresponds well with a maximum estimate of about 100m for the
1% photon flux density (PFD) in that area (Slawyk 1979).
In the Arctic
and adjacent seas the estimate for the maximum 1% PFD level is SO-60m;
during blooms this decreases to 20-30m (Ellertsen et al. 1981, Sakshaug
et al. 1981, Platt et al. 1982).
SPATIAL AND SEASONAL DISTRIBUTION OF. POLAR PHYTOPLANKTON
In spite of half a century of studies in the Antarctic, the spatial
and temporal distribution of phytoplankton is not well documented. There
are several reasons for this. First, distances are vast, the seas are
often rough, and expeditions are relatively few and very expensive. Second, the most extensive studies were done by the early researchers
(Hart 1934, 1942, Hentschel 1932), but they generally examined only
net tow samples and so included only the relatively large cells. Third,
the numerous cruises of the past 20 years have been concentrated in a
few geographical ar"eas and have generally taken place during the austral
summer period (see review by El-Sayed 1984). Some of the more valuable
quantitative data on species distributions have been obtained by the
inverted microscope method (e.g. Hasle 1969), but these studies have
been relatively few and restricted in scope. The following generalizationsemerge from all these studies.
(1) There is a richness of phytoplankton around South Georgia, with both a spring and an autumn bloom,
and the Scotia Sea also appears richer than other areas. There is,
however, a delay of the spring bloom with increasing latitude due to
light and ice effects. The "Northern Region" (Polar Front to 330 n.m.
south of it) with generally open waters exhibits a peak in early December; the "Intermediate Region" and the Scotia" Sea in January; and the
"Southern Region" (south of the Antarctic Circle) exhibits a peak in
mid-late February.
(2) The main picture from December and onwards will
consequently be one of poverty of phytoplankton in all offshore waters.
Chlorophyll is generally in the range of 0.1 to 0.3 ~g per liter (e.g.
El-Sayed 1970b).
(3) Phytoplankton blooms (>1.5 ~g chl. per liter) are
characteristic of shelf areas (300 to SOOm depth) in the Ross and Weddell Seas, around the Antarctic Peninsula, in waters over the Scotia
Ridge, and at times along receding ice egdes. Blooms in these waters