Baltic Sea ice seasons in the twentieth century

Abstract

We examine the evolution of ice seasons in the Baltic Sea during the 20th century based on a set of 37 time series from the coastal observation stations. The statistical question of combining data from sites with different ice probabilities is solved by using fractiles of the distributions. These 100 yr long time series, including date of freezing, ice break-up, number of days with ice, and maximum annual ice thickness, provide evidence of a general trend toward easier ice conditions; the largest change is in the length of ice season, which is decreasing by 14 to 44 d per century. The trends of a reduction of about 8 to 20 d per century to earliest ice break-up are in a good agreement with a warming trend in winter air temperature over Europe. A statistically significant decreasing trend in probability of ice occurrence in the southern part of the Baltic Sea was detected; however, there is no change in probability of ice occurrence in the northern part.

100 years of atmospheric and marine observations at the Finnish Utö Island in the Baltic Sea

“…This is visible in, e.g., seabed erosion (unpublished data). During the last decades, sea ice is observed at Utö every few years (Jevrejeva et al, 2004) while summertime cyanobacterial algae blooms are observed almost annually, in July or August (e.g., Kahru et al, 1994;Seppälä et al, 2007).…”

“…Recently, Utö station was selected as one of the World Meteorological Organization (WMO) long-term observing stations in the recognition of its irreplaceable cultural and scientific heritage (World Meteorological Organization, 2017). However, despite observations having started already in 1881, a limited number of meteorological studies (e.g., Riihelä et al, 2015;Laapas and Venäläinen, 2017) and only few studies focusing on sea ice and hydrography (Ahlnäs, 1961;Haapala and Alenius, 1994;Haapala and Leppäranta, 1997;Jevrejeva et al, 2004) have been published. One reason for this is that a significant part of the observation data has not been digitized or quality assured until the current study.…”

Recent Change—Sea Ice

“…Monitoring activity in the Baltic Sea is limited to the landfast ice regions, where the sea ice could be thinner than in the drift ice regions. According to Jevrejeva et al (2004), the ice thickness time series around the Baltic Sea coast does not show any consistent trend: both decreasing and increasing trends were reported. A recent study by Ronkainen (2013) supported these conclusions.…”

“…Ice Duration Jevrejeva et al (2004) has compiled the most extensive analysis of ice season changes in the Baltic Sea to date, using time series at 37 coastal stations from the Bothnian Bay to the Arkona Basin. In general, observations showed a tendency towards milder ice conditions.…”

“…The first written accounts of ice conditions in the Baltic Sea were documented in harbour logbooks of the Fourteenth century (Tarand and Nordli 2001;Schmelzer and Holfort 2011). A regular observational network was established in the nineteenth century among the Baltic Sea countries, mainly to provide guidance for shipping (Jevrejeva et al 2004), but later for scientific analyses of ice conditions (Speerschneider 1927;Jurva 1937;Palosuo 1953). In the first Baltic Sea assessment (BACC Author Team 2008), Schmelzer et al (2008) and Vihma and Haapala (2009) gave extensive summaries of the existing literature.…”