7
concept of critical depth. These ideas have been verified later by a
comprehensive set of data for the Norwegian coast (Rey 1981).
In these
areas autumn maxima are reported for near-shore areas and fjords only.
After culmination of the spring bloom nutrient depletion sets in and
oligotrophy prevails till the next growth reason.
A pattern has emerged also for Arctic regions with seasonal ice
cover. Epontic algae (under ice) may start growing modestly as early
as February and represent a primary production of 0.015-0.020 g C m- 2
day-1 (Bering Sea McRoy and Goering 1974). Later in the year, when snow
on the ice melts, increased light penetration supports some growth of
phytoplankton in waters under the ice. This limited growth appears unable to exhaust the nutrients of the surface waters. When the ice melts,
nutrient rich surface waters thus become exposed and a vigorous bloom
follows, apparently following in the wake of the retreating ice egde.
This phenomenon has been reported by several authors in the Bering Sea
(Alexander 1980, Schandelmeier and Alexander 1981), in the Beaufort Sea
(Horner and Schrader 1982), in Frobisher Bay (Grainger 1975) and in the
Barents Sea (Rey and Loeng 1984). McRoy and Goering (1974) have estimated that this bloom may contribute more than 50% of the annual primary
production in the Bering Sea. A schematic illustration is given in Fig.
4. This "ice edge" bloom culminates when nutrients become depleted,
with a maximum chlorophyll level in the range og 8-10 ~g chI. 1- 1 •
After culmination a nutrient-limited period usually sets in, of which
the duration is determined by the length of the ice-free season. It
may be short or non-existent at the very highest latitudes.
-
exp.growth ~
max. nutr.
-peak of
m_x.
bloom
grazing
I
I
nutr.
depletion
30 ~--------------------------___
E
£
:r
" 50
oligotrophic
Fig. 4. Schematical illustration of the phytoplankton bloom
in northern ice-edge waters.
Based on data from Ellertsen et
al. (1981) and Schandelmeier and
Alexander (1981).
It seems rather well documented for Arctic areas that ice melting
has two positive effects on the primary production: exposure of nutrient
rich waters to a full strength light regime and formation of a stable
water column by introduction of meltwater. Typically a pyknocline forms
at 20-30m depth at the ice edge, which is about the depth of the pyknocline in Norwegian fjords during the spring bloom.
In the Norwegian Sea
concept of critical depth. These ideas have been verified later by a
comprehensive set of data for the Norwegian coast (Rey 1981).
In these
areas autumn maxima are reported for near-shore areas and fjords only.
After culmination of the spring bloom nutrient depletion sets in and
oligotrophy prevails till the next growth reason.
A pattern has emerged also for Arctic regions with seasonal ice
cover. Epontic algae (under ice) may start growing modestly as early
as February and represent a primary production of 0.015-0.020 g C m- 2
day-1 (Bering Sea McRoy and Goering 1974). Later in the year, when snow
on the ice melts, increased light penetration supports some growth of
phytoplankton in waters under the ice. This limited growth appears unable to exhaust the nutrients of the surface waters. When the ice melts,
nutrient rich surface waters thus become exposed and a vigorous bloom
follows, apparently following in the wake of the retreating ice egde.
This phenomenon has been reported by several authors in the Bering Sea
(Alexander 1980, Schandelmeier and Alexander 1981), in the Beaufort Sea
(Horner and Schrader 1982), in Frobisher Bay (Grainger 1975) and in the
Barents Sea (Rey and Loeng 1984). McRoy and Goering (1974) have estimated that this bloom may contribute more than 50% of the annual primary
production in the Bering Sea. A schematic illustration is given in Fig.
4. This "ice edge" bloom culminates when nutrients become depleted,
with a maximum chlorophyll level in the range og 8-10 ~g chI. 1- 1 •
After culmination a nutrient-limited period usually sets in, of which
the duration is determined by the length of the ice-free season. It
may be short or non-existent at the very highest latitudes.
-
exp.growth ~
max. nutr.
-peak of
m_x.
bloom
grazing
I
I
nutr.
depletion
30 ~--------------------------___
E
£
:r
" 50
oligotrophic
Fig. 4. Schematical illustration of the phytoplankton bloom
in northern ice-edge waters.
Based on data from Ellertsen et
al. (1981) and Schandelmeier and
Alexander (1981).
It seems rather well documented for Arctic areas that ice melting
has two positive effects on the primary production: exposure of nutrient
rich waters to a full strength light regime and formation of a stable
water column by introduction of meltwater. Typically a pyknocline forms
at 20-30m depth at the ice edge, which is about the depth of the pyknocline in Norwegian fjords during the spring bloom.
In the Norwegian Sea