International Polar Year 2007–2008 - WMO

Fig. 2.2-11. The
acoustic data from
ADCPs (acoustic
Doppler current
profilers) provides a
means of monitoring
the backscatter levels
(linked to biomass)
through the water
column. The banded
pattern of backscatter
is characteristic of
DVM with biomass
remaining deep at
noon and ascending
into the surface at
night (Cottier et al.,
2006).
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IPY 20 07–20 08
the transport of energy to higher trophic levels, such
as fish, birds and mammals.
One of the key results of CLEOPATRA has been to
demonstrate the critical importance of ice algae for high
latitude ice covered ecosystems. In Rijpfjorden in 2007,
ice algae was the only available food for grazers during
the months from April to June. Ice broke up and left the
fjord mid-July while a phytoplankton bloom developed
in late-June to early-July. This phytoplankton bloom
peaked two months after the ice algae bloom. The food
quality of the ice algae and phytoplankton blooms was
the same, but highest food quality, i.e. highest amount
of polyunsaturated fatty acids (PUFAs), was early in the
growth phase of each bloom. Calanus glacialis is the
key grazer in ice covered shelf ecosystems and is a very
important, energy rich food item for larger zooplankton,
fish and sea birds. Observations from Rijpfjorden have
shown that C. glacialis can time its reproduction to
match both the ice algae and phytoplankton blooms.
Ice algae fuelled high egg production in C. glacialis,
allowing early reproduction so the offspring can then
fully exploit the later-occurring phytoplankton bloom.
By utilizing both ice algae and phytoplankton, C.
glacialis extends its growth season substantially, which
can explain the success of this species (up to 80% of
the mesozooplankton biomass) in arctic shelf seas.
Future climatic scenarios with less or no sea ice may
have negative impacts on the population growth of
C. glacialis, which may have severe impacts on higher
trophic levels in arctic shelf seas.
A second main result of the project concerned the
study of the impact of sea ice cover on zooplankton
behaviour. One of the great unknowns of arctic
ecosystems is the status of winter communities and
the processes that are active. The classic paradigm
of marine ecosystems holds that most biological
processes will slow or cease during the polar night
and one key process that is generally assumed to
cease during winter is Diel Vertical Migration (DVM)
of zooplankton, the biggest synchronized shift of
biomass on the Planet. Using acoustic data collected
from the moorings in Kongsfjorden and Rijpfjorden,
it can be demonstrated that synchronized DVM of
zooplankton continues throughout the Arctic winter,
in both open water and under sea ice (Fig. 2.2-11; Berge
et al., 2008). It is possible that the sensitivity of these
organisms to light is so acute that even during the high
arctic polar night, DVM is regulated by diel variations
in illumination at intensities far below the threshold
for human perception. The full winter data set shows
that DVM is stronger in open waters compared to
ice-covered waters, implying that the active vertical
flux of carbon will become more effective if there is a
continued retreat of the arctic winter sea-ice cover.
Pacific Sector
Northward shift in the ecosystem of the Bering Sea.
Drawing together a large body of evidence, Grebmeier
et al., (2006) have described a major ecosystem shift in
the Northern Bering Sea since the late 1970s. A system
characterized by extensive seasonal sea-ice cover,
high water column and sediment carbon production,
and a tight pelagic-benthic coupling of organic
production gave way to a reduction in sea ice, an
increase in air and ocean temperatures, an increase in
pelagic fish and a geographic displacement of marine
mammal populations coincident with a reduction of
their benthic prey populations. A telling point of detail
has been the reduction in sediment oxygen uptake
south of St Lawrence Island between 1988 and 2004,
from ~40 to about 12 mmol O 2 m- 2 day- 1 (Grebmeier