29
Australia on a south-bound transect (however, they also reported low
concentrations at the Polar Front during the north-bound leg of the
same cruise).
Interestingly, Kennett (1977) contends that the high
rates of siliceous biogenic sedimentation at the Polar Front may be
indicative of substantial primary production in the surface waters of
this region.
If the Antarctic waters were generally well mixed vertically, the instability of the water column within the Polar Front would
not have as pronounced an effect on chlorophyll ~ concentration as has
been previously suggested. Thus, the high standing crop and primary
productivity at the Polar Front will have to be explained in terms
other than the stability or instability or instability of the water
column. At present it is difficult to speculate on the factors contributing to the high standing crop of phytoplankton observed at the
Polar Front region.
E.
Grazing
In the Southern Ocean, euphausiids (principally Euphausia
superba), which may constitute half of the Antarctic zooplankton (Ho1dgate, 1970), are the dominant herbivores.
Several investigators have
observed that areas of high krill concentration are usually noted for
their low standing crop of phytoplankton. During the First International BIOMASS Experiment (FIBEX), Polish investigators found that in
the central parts of the Bransfield Strait, areas of dense krill concentration exhibited low chlorophyll a values at uhe surface (~0.5
3
-
2
mg/m ) and in the water column « 50 mg/m) (Lipski, personal commuication). Chilean scientists, also during the FIBEX, reported similar
findings.
Thus in the region to the south of the South Shetland Islands, Uribe (1982) found low values of chlorophyll ~ « 0.5 mg/m 3 )in
the central part of the Bransfield Strait where high krill concentration in the 10-200 m layer was found. According to Uribe (1982) the
poverty of the phytoplankton was not due to nutrient limitation (phosphate: 1.4 ~g.at/1; nitrate: 17.9 ~g.at/1), but most likely to intensive
krill feeding.
Further, the data from the R/V MELVILLE cruise (also
during FIBEX) demonstrate on a temporal basis the inverse relationship
often noted between phytoplankton biomass and zooplankton (mainly krill)
abundance (Holm-Hansen and Hunt1ey,in press).
IV. DISCUSSION
The general picture that emerges from the above investigations
is the great variability of the phytoplankton biomass and primary
Australia on a south-bound transect (however, they also reported low
concentrations at the Polar Front during the north-bound leg of the
same cruise).
Interestingly, Kennett (1977) contends that the high
rates of siliceous biogenic sedimentation at the Polar Front may be
indicative of substantial primary production in the surface waters of
this region.
If the Antarctic waters were generally well mixed vertically, the instability of the water column within the Polar Front would
not have as pronounced an effect on chlorophyll ~ concentration as has
been previously suggested. Thus, the high standing crop and primary
productivity at the Polar Front will have to be explained in terms
other than the stability or instability or instability of the water
column. At present it is difficult to speculate on the factors contributing to the high standing crop of phytoplankton observed at the
Polar Front region.
E.
Grazing
In the Southern Ocean, euphausiids (principally Euphausia
superba), which may constitute half of the Antarctic zooplankton (Ho1dgate, 1970), are the dominant herbivores.
Several investigators have
observed that areas of high krill concentration are usually noted for
their low standing crop of phytoplankton. During the First International BIOMASS Experiment (FIBEX), Polish investigators found that in
the central parts of the Bransfield Strait, areas of dense krill concentration exhibited low chlorophyll a values at uhe surface (~0.5
3
-
2
mg/m ) and in the water column « 50 mg/m) (Lipski, personal commuication). Chilean scientists, also during the FIBEX, reported similar
findings.
Thus in the region to the south of the South Shetland Islands, Uribe (1982) found low values of chlorophyll ~ « 0.5 mg/m 3 )in
the central part of the Bransfield Strait where high krill concentration in the 10-200 m layer was found. According to Uribe (1982) the
poverty of the phytoplankton was not due to nutrient limitation (phosphate: 1.4 ~g.at/1; nitrate: 17.9 ~g.at/1), but most likely to intensive
krill feeding.
Further, the data from the R/V MELVILLE cruise (also
during FIBEX) demonstrate on a temporal basis the inverse relationship
often noted between phytoplankton biomass and zooplankton (mainly krill)
abundance (Holm-Hansen and Hunt1ey,in press).
IV. DISCUSSION
The general picture that emerges from the above investigations
is the great variability of the phytoplankton biomass and primary