8 Recent Change—Sea Ice 151
Table 8.2 Change in
freezing date, break-up date, length of ice
season and ice thickness
in the Finnish coastal zone
of the Baltic Sea
Kemi, Bothnian Bay
Uto, Archipelago Sea
Loviisa, Gulf of Finland
Probability of ice appearance
1.00
0.81
1.00
Trend 100 year -1
0
-0.19
0
Freezing date
Number of observations
112
97
106
Mean date
10 Nov
27 Jan
7 Dec
Trend (days 100 year -1 )
7
(24)
20
Trend pre-1950 (days 100 year -1 )
12
(65)
25
Trend post-1950 (days 100 year -1 )
0
(-15)
24
Break-up date
Number of observations
113
97
10
Mean date
20 May
9 Apr
24 Apr
Trend (days 100 year -1 )
-11
(-16)
-20
Trend pre-1950 (days 100 year -1 )
-5
(-D
-8
Trend post-1950 (days 100 year -1 )
-17
(-34)
-38
Length of ice season
Number of observations
113
121
102
Mean (days)
190
50
137
Trend (days 100 year -1 )
-18
-46
-41
Trend pre-1950 (days 100 year -1 )
-17
-84
-32
Trend post-1950 (days 100 year -1 )
-16
-36
-62
Ice thickness
Number of observations
94
81
Mean (cm)
73
46
Trend (cm 100 year -1 )
9
-25
Trend pre-1950 (cm 100 year -1 )
13
-29
Trend post-1950 (cm 100 year -1 )
4
-52
Data for three sites: Kemi (1890-2010), Uto (1889-2010) and Loviisa (1894—2010) (Ronkainen 2013). The parentheses indicate values that are not
based on all data because the probability of ice occurrence is less than one
■ 1961-1990(max) ■ 1971-2000(max) ■ 1981-2010(max)
• 1961-1990<with ice) • 1971 -2000{with ice) • 1981-2010(with ice)
Fig. 8.7 Mean number of days with ice (all winters), mean number of days with ice (only winters with ice) and maximum number of days with ice
on the southern Baltic Sea coast in the 30-year periods 1961-1990, 1971-2000 and 1981-2010 (Schmelzer et al. 2012)
Kemi), ice thickness shows a slight increasing trend (+9 cm)
over the past 100 years, while in the Gulf of Finland, a
thinning trend is observed (-25 cm).
In the southern Baltic Sea, ice thickness in the sheltered
coastal waters reached 10-20 cm on average, and as much as
40-62 cm in the extremely hard ice winter of 1962/63
(Fig. 8.8). In most parts of the Baltic Sea offshore waters, ice
thickness reaches 5-20 cm, but in particularly cold and long
winters, the ice grows to 50 cm thickness in some areas. A
maximum ice thickness of 70 cm was reached in the Kiel
and Lübeck bays and in the waters of Rügen in the winter of
1962/63. In Szczecin Lagoon, in the Bay of Puck and in
Vistula Lagoon, the ice reached 62 cm thickness. Since
1971, the maximum ice thickness has been about 50 cm in
the southern Baltic Sea coast and up to 30 cm in the sea area
north of Rügen.
