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Summary
The
goal of the project was to assess potential transport of pollutants
from the Kara sea to to the Barents sea.
The project was divided into a subproject on statistical
description of ice drift and sediment uptake into sea ice.
The studies also included descriptions of the distribution of
open water where ice crystals may form and pick up sediments from the
water. This work resulted
in several manuscripts for publication and it contributed to a PhD
thesis.
A quantitative assessment was made of the transport of sediment borne
contaminants by sea ice, based on the work on uptake mechanisms, ice
drift and the studies in the pollution section of the programme. The
evaluation was carried out for a variety of contaminants (heavy metals,
radionuclides, persistent organic pollutants). The results indicate a
lower contaminant transport under more realistic conditions than
previous calculations based on worst-case scenarios.
Scientific results
One
main focus was a statistical description of ice drift from the Kara
Sea into the Barents Sea.
Ice formed at the outlet of Ob and Yenisey drift with a
probability of about 50 percent into the Barents Sea within 2-3 years.
If an ice particle in the Kara Sea does not reach the Barents
Sea within about 4 years, is would likely have drifted out of the
Arctic Basin through the Fram Strait into the Greenland Sea where it
melts.
A main
manuscript for publication from this work is:
Korsnes,
R. and Pavlova, O.: "Assessment of potential transport of
pollutants into the Barents Sea via sea ice - an observational
approach", This work gives statistics on ice drift based on
reconstruction of monthly ice drift in the Arctic 1899-1998 (100 years).
Another
focus for work was to understand how sediments may be included into
sea ice in the Kara Sea from freely moving ice crystals in the water
picking up sediments.
This process can result in ice where the concentration of
sediments are much higher than in the free water.
The effectiveness of this concentration of sediments into the
ice depends on wind, temperature, concentration of sediments in the
water and the stratification of the water.
It also depends of the distribution of open water within the
ice field.
It seems that the existence of small openings in the ice
contributes most to sediment uptake into ice during the coldest part
of the winter.
However, sediments also comes into ice during the freeze-up in
the autumn.
This sediment uptake depends much on wind conditions during
autumn.
A special study was on deformation and distributions cracks/floe
size.
The main
publications from this work are:
Karl
Eidsvik: "Coagulation of suspended sediments and ice crystals
below leads",
Published in Cold Regions Science and Technology
and
a PhD thesis work by Lars Henrik Smedsrud.
Contaminant uptake during ice
formation is sensitive to the amount of sediment injected into the ice
during the freezing process. Comparing four different years, sediment
incorporation ranged from a low of 5.8 in 1987 to a high of 58 in
1976, or a factor of 10. Naturally, contaminant fluxes also vary among
the different years in association with the variability in sediment
uptake by sea ice. However, it is apparent that even with this
variability, the fluxes are considerably smaller than would be
predicted based on the worst-case scenario (theoretical limit). The
worst-case scenario represents the unrealistic condition that during
all storm events the maximum amount of sediment is always incorporated
into sea ice. This assumption is unrealistic because wind forced
mixing which entrains sediments into ice, is highly intermittent in
both time and space.
Based on this
assessment of realistic conditions during several different years, the
fluxes of important heavy metals, radionuclides and persistent organic
pollutants, have been quantified. Contaminant fluxes associated with
the process of frazil ice formation in the Kara sea are much smaller
than worst-case estimates. For example, fluxes of the radionuclide
Cs-137 determined for the years 1976, 1985, 1987 and 1988 are 2%-16%
of the worst-case scenario value of 8.3 x 1012 Bq/yr. Based
on these results, the amount of sediment and contaminants incorporated
into sea ice is lower than previously thought.
These calculations
are documented in Jo Lynn Carrol: Contaminant fluxes in sediment-laden sea ice from the Kara Sea..
The results will be submitted for a journal.
Relevance for
monitoring
The
work contributes to make a system for regular monitoring of sediment
transport in the Arctic and to monitor possible releases of sediments
and pollutants from ice when it melts.
Such a monitoring system could give indicators for direct
uptake of pollutants into the marine food web where algae grow in
water affected by ice melting. This
type of monitoring requires a combination of modelling and use of
satellite data.
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