Lindemann et af.: Particle Entrainment into Newlv Forming Sea Ice
121
(i) the sampled ice was already formed, (ii) the ice was drifting and therefore not in place of its
formation and (iii) low a l8 0 values of the ice samples suggest an origin near the river mouth
(H. Eicken, pers. comm. 1997). The latter one also supports the assumption that the sediments
were incorporated into the ice without beeing deposited before on the sea floor. Although
resuspension of bottom sediments due to wave action and/or bottom currents, for instance tidal
currents, cannot be completely excluded, resuspension processes do not appear neccessary for
sediment entrainment into sea ice. Subsequently, rafting of sediment-laden young ice will lead
to ice thickening and to stacked sediment layers, each of which some centimetres thick. Such
sediment layers have been observed from vessels during ice breaking (Figure 7), or in ice cores
of thick first-year ice.
Figure 7: Cross section of a vertically tilted first-year ice floe in the Laptev Sea. Rafting of former young ice
thickened, and built up the entire floe. Each bar segment is 0.5 m in length. The photograph was taken vertically
to the ice surface from aboard R/V "Polarstern" during the cruise ARK XIII. Fu = floe underside. fs = floe
surface, sf = rafted sediment-laden floes of former young ice (dark layers represent sediment inclusions), ow =
open water.
Sediment transport by sea ice
Although the observed high drift velocities of the young sea ice are only estimates, they suggest
that incorporated sediments, may be transported over long distances in relatively short time
periods.
In order to export sea ice and incorporated sediments out of the Laptev Sea shelf area, the ice
must drift in a northerly direction. Off-shore winds from south-east to south-west will force ice
motion into such a direction. As shown in Figure 4, such wind directions were observed over
several days during the freeze-up in October 1995. Because the ice cover was mainly composed
of thin, shallow-draught ice, including patches of open water, conditions for high drift
velocities were favourable. Hence, export of sea ice and incorporated sediments from nearshore areas of the Laptev Sea towards the deep Arctic Ocean is most likely during the freeze-up
in autumn, even under calm conditions.
Conlusion and Perspectives
I In October 1995, the freeze-up period in the Laptev Sea was characterized by calm weather.
Nevertheless, significant particle concentration in the newly formed ice as compared to the
underlying water column were found.
2 Pressure oscillations, linked to wave fields propagating into sea ice, and additionally
121
(i) the sampled ice was already formed, (ii) the ice was drifting and therefore not in place of its
formation and (iii) low a l8 0 values of the ice samples suggest an origin near the river mouth
(H. Eicken, pers. comm. 1997). The latter one also supports the assumption that the sediments
were incorporated into the ice without beeing deposited before on the sea floor. Although
resuspension of bottom sediments due to wave action and/or bottom currents, for instance tidal
currents, cannot be completely excluded, resuspension processes do not appear neccessary for
sediment entrainment into sea ice. Subsequently, rafting of sediment-laden young ice will lead
to ice thickening and to stacked sediment layers, each of which some centimetres thick. Such
sediment layers have been observed from vessels during ice breaking (Figure 7), or in ice cores
of thick first-year ice.
Figure 7: Cross section of a vertically tilted first-year ice floe in the Laptev Sea. Rafting of former young ice
thickened, and built up the entire floe. Each bar segment is 0.5 m in length. The photograph was taken vertically
to the ice surface from aboard R/V "Polarstern" during the cruise ARK XIII. Fu = floe underside. fs = floe
surface, sf = rafted sediment-laden floes of former young ice (dark layers represent sediment inclusions), ow =
open water.
Sediment transport by sea ice
Although the observed high drift velocities of the young sea ice are only estimates, they suggest
that incorporated sediments, may be transported over long distances in relatively short time
periods.
In order to export sea ice and incorporated sediments out of the Laptev Sea shelf area, the ice
must drift in a northerly direction. Off-shore winds from south-east to south-west will force ice
motion into such a direction. As shown in Figure 4, such wind directions were observed over
several days during the freeze-up in October 1995. Because the ice cover was mainly composed
of thin, shallow-draught ice, including patches of open water, conditions for high drift
velocities were favourable. Hence, export of sea ice and incorporated sediments from nearshore areas of the Laptev Sea towards the deep Arctic Ocean is most likely during the freeze-up
in autumn, even under calm conditions.
Conlusion and Perspectives
I In October 1995, the freeze-up period in the Laptev Sea was characterized by calm weather.
Nevertheless, significant particle concentration in the newly formed ice as compared to the
underlying water column were found.
2 Pressure oscillations, linked to wave fields propagating into sea ice, and additionally