The Davis Strait - DCE - Nationalt Center for Miljø og Energi

4 Biological environment
4.1 Primary productivity
Michael Dünweber (AU)
4.1.1 General context
The waters off West Greenland are characterised by low species diversity
whereas primary production is relatively high. Due to the presence of winter
ice in many areas and the marked variation in solar radiation, however,
primary production is often highly seasonal with an intensive phytoplankton
bloom in spring.
The Arctic oceans generally have a brief and intense phytoplankton bloom
immediately after break-up of the sea ice. This is characterised by high (transient)
biomass and a grazing food web dominated by large copepods, i.e.
Calanus, but relatively low total primary production averaged over depth
and season. However, this general picture is modified by the presence of
large polynyas, where sea ice breaking up early and nutrients being made
available from upwelling lead locally to very high production.
Development of the phytoplankton (microscopic algae) bloom in spring
gives a peak in the primary production in the water column and is the single
most important event determining the productive capacity of Arctic marine
food webs. The time of the onset of the spring phytoplankton bloom (i.e.
spring bloom) varies each year according to the duration of the winter sea
ice cover, oceanography and meteorological conditions. The spring bloom
develops when the water column is stabilised and retreat of the sea-ice cover
and solar input penetrates into the water column. The spring bloom quickly
depletes the surface layers (the euphotic zone) of nutrients, inhibiting primary
production for some time.
4.1.2 Productivity at the sea-ice edge and marginal ice zone
At ice edges the spring bloom is often earlier than in ice-free waters due to
the stabilising effect of the ice on the water column. Here, the bloom can be
very intense and attracts species of seabirds and marine mammals which often
occur and congregate along ice edges and in the marginal ice zones
(Frederiksen et al. 2008). Ice edges are not stable over time, and their distribution
varies according to oceanographic and climatic conditions. However,
at sites where nutrients are continuously brought to the uppermost water
layers, e.g. by hydrodynamic discontinuities such as upwelling or fronts,
primary production and hot spots may occur throughout the summer. The
underside of the sea ice has its own special biological community with algae,
invertebrates and fish. In spring when the light increases, this community
can be very productive. There is limited knowledge on sea-ice communities
in the assessment area, but see section 4.5 for the information available.
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