[ARCHIVE] Baltic Sea Ice Extent from Observations Reprocessing

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'''DEFINITION'''

Sea ice extent is defined as the area covered by sea ice, that is the area of the ocean having more than 15% sea ice concentration. Sea ice concentration is the fractional coverage of an ocean area covered with sea ice. Daily sea ice extent values are computed from the daily sea ice concentration maps. All sea ice covering the Baltic Sea is included, except for lake ice. The data used to produce the charts are Synthetic Aperture Radar images as well as in situ observations from ice breakers (Uiboupin et al., 2010). The annual course of the sea ice extent has been calculated as daily mean ice extent for each day-of-year over the period October 1992 – September 2014. Weekly smoothed time series of the sea ice extent have been calculated from daily values using a 7-day moving average filter.

'''CONTEXT'''

Sea ice coverage has a vital role in the annual course of physical and ecological conditions in the Baltic Sea. Moreover, it is an important parameter for safe winter navigation. The presence of sea ice cover sets special requirements for navigation, both for the construction of the ships and their behavior in ice, as in many cases, merchant ships need icebreaker assistance. Temporal trends of the sea ice extent could be a valuable indicator of the climate change signal in the Baltic Sea region. It has been estimated that a 1 °C increase in the average air temperature results in the retreat of ice-covered area in the Baltic Sea about 45,000 km2 (Granskog et al., 2006). Decrease in maximum ice extent may influence vertical stratification of the Baltic Sea (Hordoir and Meier, 2012) and affect the onset of the spring bloom (Eilola et al., 2013). In addition, statistical sea ice coverage information is crucial for planning of coastal and offshore construction. Therefore, the knowledge about ice conditions and their variability is required and monitored in Copernicus Marine Service.

'''KEY FINDINGS'''

Sea ice in the Baltic Sea exhibits a strong seasonal pattern. Typically, formation begins in October and can persist until June. The 2022/23 ice season saw a relatively low maximum ice extent in the Baltic Sea, peaking at around 65,000 km². Formation started in November and accelerated in the second week of December. The ice extent then remained fairly stable and below the climatological average until the end of January. From February to the second week of March, the extent of sea ice steadily grew to its maximum of 65,000 km², before gradually receding. The peak day for sea ice extent varies annually but generally oscillates between the end of February and the start of March (Singh et al., 2024). The past 30 years saw the highest sea ice extent at 260,000 km² in 2010/11. Despite a downward trend in sea ice extent in the Baltic Sea from 1993 to 2022, the linear trend does not show statistical significance.

'''DOI (product):''' https://doi.org/10.48670/moi-00200