Multi year ice

Sea ice in the Arctic and Antarctic can be classified into several types, the main ones being

• young ice (YI): thin (up to 30 cm thick) new ice; includes a few sub-types; can be smooth or rough
• first-year ice (FYI): formed during one cold season; thickness above 30 cm; surface can be level, rough or with ridges
• multiyear ice (MYI): ice that has survived at least one melt season; less saline and often rougher than FYI, but topographic features are generally smoother than FYI

The physical properties of sea ice differ significantly for the different ice types. Therefore, knowledge of the sea ice type is important for a number of activities including marine navigation and modelling of the ice-ocean-atmosphere system and also for remote sensing of other quantities related to sea ice such as the depth of the snow layer on top of it. With the recent accelerated decrease of MYI in the Artic, mapping this ice type on a daily basis has become important for many applications.

The MYI data on this site are from a new satellite-based retrieval of sea ice type in the Arctic which can in principle distinguish YI, FYI and MYI. The retrieval method uses active and passive microwave data (radar scatterometer and radiometer, respectively). The former are acquired by the sensor ASCAT on the Metop satellites. Until 2015, data regridded to the common 12.5 km North polar stereographic grid (“NSIDC grid”) by Ifremer/CERSAT were taken. After that, near-real time ASCAT data were regridded by the University of Bremen (Institute of Environmental Physics). The passive microwave data are from either AMSR-E on the Aqua satellite by NASA (until 2011) or from AMSR2 on the GCOM-W1 satellite by JAXA (since 2012).
This retrieval was originally developed for the Arctic and has recently been adapted for Antarctic conditions as well. More information about the retrieval method and the algorithm (multi year ice) can be found here.

Directly at the coast, the signal of the scatterometer or radiometer data can contain a contribution from the land, resulting in errors in the MYI concentration. Therefore, during the first 10 days of the season (end of September) a zone that is one pixel wide, along all coasts, is cleared of MYI unless connected to MYI offshore.

Finally, surface temperature data and sea ice drift data are used in several correction schemes which are applied to account for the effect of melt-refreeze processes, snow metamorphosis and sea ice drift on the sea ice type retrieval. However, it should be noted that weather influence on the surface of the MYI (including the snow cover) can be the reason for considerable day-to-day fluctuation of MYI concentration and in the Eastern Arctic (Kara and Laptev Sea), unrealistically high MYI concentrations occur in March and April probably due to small areas of spurious MYI caused by rough young ice (possible with wet snow) in the previous autumn. More information on the retrieval algorithm and the data sources can be found here (https://seaice.uni-bremen.de/multiyear-ice-concentration/information/).

Data on multiyear sea ice in the Arctic and Antarctic are available for the period from 2012 to present and 2013 to present, respectively, and are provided by the University of Bremen (Institute of Environmental Physics). As the retrieval does not work during the melt season, the data record usually spans October to May (Arctic) and February to October (Antarctic).

Note: For the data on multiyear sea ice provided here (especially for the Antarctic), no claim to accuracy can be guaranteed at present. Please also refer to the corresponding notes provided here.