SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

Research
tronics and data links; Michel Mitchell (our
physical scientist) developed the data
acquisition and computer interfacing while
both he and Jeff Spry (our biologist)
supervised the field logistics and
experiments.
Sampling of ice algae and zooplankton
have been traditionally approached by
using divers who sample the underice
waters by removing ice samples, implanting
chambers in the underice surface for the
measurement of algal growth or deploying
suction devices for capturing zooplankton.
The major problem with diver sampling is
the contamination of the underice surface
by air bubbles and subsequent penetration
of air into the porous ice thereby nullifying
these measurements. Our approach to
developing samplers has been to deploy
instruments remotely from the ice surface
through ice holes which could be augered
in a relatively short time (~2 min). These
holes would be relatively small in diameter,
about 22-25 cm. The device would be
deployed through the ice hole and then
made to ‘reach out’ horizontally at some
distance from the hole (~1 m) in order to
sample an undisturbed region of the ice.
Fig. 2 The underice pumping arm used for
sampling zooplankton The operational zooplankton
and chlorophyll were accomplished
with a plankton counter and fluorometer on the
ice surface.
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The first device developed to accomplish
this type of sampling was the underice
pumping arm shown in Figure 2. The
sampler arm mounted on a mast is deployed
through the ice hole in a folded
position. Once clear of the hole, the arm is
released by a trip wire pulled from the
surface. A tension spring located at the
elbow provides the force necessary to
rotate the arm which is then locked in the
90° sampling position (shown in Figure 2).
The arm can then be moved to the
underice surface. When sampling is completed,
the trip wire is again pulled,
releasing the arm to the 180° position and
allowing recovery through the ice hole.
The underice arm now provides a vehicle
for deploying and carrying various sensors
and collecting samples.
The first sampling problem approached
was that of measuring zooplankton concentrations
within a meter of the underice
surface. The underice arm shown in Figure
2 can be easily used as a profiler within a
few meters of depth from the ice surface.
Water, pumped to surface from a nozzle
attached to end of the arm, was filtered in
a cod end bucket for later analysis.
The pumped outflow can also be transferred
to an electronic zooplankton counter
(Herman, 1988) measuring zooplankton
concentrations and sizing all animals. A
fraction of the outflow was also transferred
to a Turner fluorometer measuring chlorophyll
concentrations (the indicator of algal
Fig. 3 The reflectance meter used to detect algal layers in the underice surface.
biomass) in the near surface water. Both
instruments were housed in an insulated
box and powered by a portable generator.
The entire system was portable and could
be transported by snowmobile and sled.
Initial data and results from the pumping
arm revealed two startling facts. First, the
Arctic copepod Pseudocalanus was highly
aggregated in the first 10 cm under landfast
ice (Conover, et al, 1986) during spring,
reaching concentrations as high as 10 6 per
cubic meter. Second, the lack of any
significant algal concentrations in the
immediate upper water layer suggested that
these copepods were utilizing the ice algae
directly.
The second sampling problem was that
of measuring the distribution of algae
within the bottom ice layers. Fluorometric
techniques usually employed in the oceans
were ineffective since algal concentrations
were too high and would ‘quench’ the light
signals within the first millimeter of ice
layer. Optical penetration of the algal
layers with an intense light beam was
necessary so that the degree of reflection of
light by these algal layers could be used as
the measure of these concentrations. The
instrument design is shown in Figure 3. An
intensive infrared (IR) beam is focused into
a thin slice with dimensions 2 mm thick
and 2 cm deep (looking into the page,
Figure 3) and directed into the ice at an
angle of 45°. An algal layer (e.g. at 2 cm
depth, Figure 3) will reflect light back into