Geology Reference
In-Depth Information
(a)
(b)
Figure 1.10
Calving season for seals on sea ice in the Labrador Sea: (a) mothers and (b) a puppy (photos of
N. K. Sinha, March 1989, unpublished).
primary production in the Arctic (25%) and in the
Antarctic (20%) [
Legendre et al.
, 1992]. About 200 spe-
cies are found in Arctic sea ice, the most common among
them is diatoms. These microorganisms sustain the sec-
ondary production and that, in turn, supports life of all
marine animals including fish, birds, seals, bears, and
many others, all the way to the killer whales.
In addition to nutrients, the survival of these organisms
hinges upon the availability of light that penetrates the
ice sheet to reach the depth where sufficient nutrients are
available for organisms to grow. This is known as photo-
synthetically active radiation (PAR). While sea ice
absorbs most of the incident light and the snow cover
reflects most of it, the PAR at 1 m depth of an ice sheet
represents only 1%-5% of the visible spectrum that pen-
etrates the sheet. Incorporation of microorganisms from
the water column into the sea ice may occur during the ice
formation. However, high concentrations of microalgae
have been observed during the springtime within the
interstices of the lower margin of sea ice floes. In early
spring the Sun starts to shine after the end of long polar
nights, and the PAR reaching the bottom of the ice sheet
(can be 2 m thick) would be sufficient for the alga growth.
Microalgae tend to concentrate in the bottom ice layers
because it is more favorable microhabitat than the surface
layers. This is due to less stressful temperature and higher
saline environment. Nevertheless, microalgae are also
often found in a thin layer of seawater immediately under
the water‐ice interface. For at least 1-3 months, ice algal
blooms enhance and extend biological production in polar
waters. Depending largely on climatic and environmental
variability, biomass accumulation of sea ice algal popula-
tions eventually depends upon the duration of their growth
season. More information on biomass accumulation at
the bottom of the ice is presented in section 4.5.4.
1.4.7. Sea Ice and Offshore Structures
For offshore structures—both floating and fixed,
including near shore structures such as docks and ports,
and vessels in ice‐rich waters—the influence of sea ice is
probably the most significant factors to be considered by
the designers and structural engineers. Structural frame-
works and their mass must be able to withstand the local
and overall forces exerted by moving ice. The structures
must be protected from encroachments of ice using ice
information managements (with the help of remote sens-
ing). The movements of the ice could be continuous or
intermittent. The ice could be first year, second year, or
multiyear, flat floes, or rafted and ridged, and may con-
sist of bergybits or icebergs. Development of new tech-
nologies for exploration for undiscovered oil and gas in
the Arctic, construction of environmentally friendly pro-
duction drilling platforms, transportation of gas and oil
from such remote parts of the globe, and avoidance of oil
spills and cleanup in case of accidents are some of the
huge challenges to the energy industry with high‐technol-
ogy demands on structures, vessels, and pipelines.
During ice‐structure interactions, there is only one
choice. Ice must fail, not the structure. Figure 1.11 depicts
a notch in a second‐year (SY) sea ice floe, in northern
Baffin Bay, made during a dedicated ramming event by
the ice breaking, bulk carrier,
MV Arctic
in June 1984.
During this planned ice breaking expedition, old ice floes
were instrumented and ice characteristics were recorded
before conducting the tests. The CCG icebreaker,
Louis
