Baltic Sea Ice Climate Workshop 2005 
34 
To examine the ice dynamics in the Northern Quark, idealised simulations were performed with 
a sea ice mechanics model calibrated for relatively small-scale problems as here (Wang et al., 
2003). This is a viscous-plastic three-level model, which predicts the evolution of sea ice 
velocity, compactness, thickness of undeformed ice and thickness of deformed ice as forced by 
the wind field. The initial situation was specified by ice compactness equal to 0.95 in the 
Northern Quark and bay of Bothnia, while the Sea of Bothnia was ice-free. The wind was 10 
m/s from northeast, driving the ice field of the Bay of Bothnia down. The initial ice thickness 
was varied, as was the extent of the fast ice zone. 
Fig. 6 shows the result when the initial ice thickness was 10 cm and the fast ice boundary was 
taken as the 5-m depth contour of the sea. In south the ice flows out into the Sea of Bothnia, 
and in the Northern Quark above the narrow throughflow a heave ridging takes place with ice 
thicknesses almost 50 cm from this mechanical accumulation. On the northern fast ice 
boundary the lead opens up. Increasing the initial thickness to 80 cm, there was still 
throughflow but the less ridging took place. Extending the fast ice zone to the 10-m depth 
contour resulted in a large change, with almost no throughflow left in both initially thin ice (10 
cm) and thick ice (cases). As thin ice is heavily ridging, it gains strength and becomes stuck. 
The critical point is therefore the geometry of the strait. 
Initial ice thickness (cm) 
63 * * * 
18 19 20 21 22 23 24 25 26 
72 hours forecast 
63 ■ * ■ 
18 19 20 21 22 23 24 25 26 
Longitude (°N) 
96 hours forecast 
18 19 28 21 22 23 24 25 26 
Longitude (*N) 
12Q hours forecast 
18 19 28 21 22 23 24 25 26 
Longitude (*N) 
Fig. 6. Model simulation of the throughflow of the ice in the Northern Quark. The initial ice 
thickness and compactness are 10 cm and 0.95, and the wind blows from 20° right from north. 
The initial situation and predictions at one-day time step are shown. 
Conclusions 
Sea ice investigations were initiated in 2004 off Umea in the Northern Quark, Baltic Sea, as a 
part of our costal zone winter programme. In 18 November 2004 a float was deployed at the