Abstract
Polar sea ice is one of the Earth’s climate components that has been significantly affected by the recent trend of global warming. While the sea ice area in the Arctic has been decreasing at a rate of about 4 % per decade, the multi-year ice (MYI), also called perennial ice, is decreasing at a faster rate of 10 %–15 % per decade. On the other hand, the sea ice area in the Antarctic region was slowly increasing at a rate of about 1.5 % per decade until 2014 and since then it has fluctuated without a clear trend. However, no data about ice type areas are available from that region, particularly of MYI. Due to differences in physical and crystalline structural properties of sea ice and snow between the two polar regions, it has become difficult to identify ice types in the Antarctic. Until recently, no method has existed to monitor the distribution and temporal development of Antarctic ice types, particularly MYI throughout the freezing season and on decadal time scales. In this study, we have adapted a method for retrieving Arctic sea ice types and partial concentrations using microwave satellite observations to fit the Antarctic sea ice conditions. The first circumpolar, long-term time series of Antarctic sea ice types; MYI, first-year ice and young ice is being established, so far covering years 2013–2019. Qualitative comparison with synthetic aperture radar data, with charts of the development stage of the sea ice, and with Antarctic polynya distribution data show that the retrieved ice types, in particular the MYI, are reasonable. Although there are still some shortcomings, the new retrieval for the first time allows insight into the evolution and dynamics of Antarctic sea ice types. The current time series can in principle be extended backwards to start in the year 2002 and can be continued with current and future sensors.
Highlights
As an important component of the global climate system, sea ice affects and reflects changes in other climate components, 20 controls energy and gas fluxes between ocean and atmosphere in polar regions, and it is an important part of the polar marine ecosystem
The sea ice type retrieval method Environment Canada’s Ice Concentration Extractor (ECICE) (Shokr et al, 2008; Shokr and Agnew, 2013) and the subsequent correction schemes for multiyear ice (MYI) (Ye et al, 2016a, b) developed for the Arctic can be adapted for the Antarctic, given samples of Antarctic ice types
Maps of uncorrected young ice (YI), first-year ice (FYI) and MYI, and of MYI corrected for effects of melt-refreeze and snow metamorphosis, can be retrieved, outside the melt season, at spatial resolution of 12.5 km
Summary
As an important component of the global climate system, sea ice affects and reflects changes in other climate components, 20 controls energy and gas fluxes between ocean and atmosphere in polar regions, and it is an important part of the polar marine ecosystem. The MYI area of the Antarctic may have followed an increasing trend, based on the fact that in the Austral summer the sea ice extent of the Antarctic has increased by 3.6% per decade from 1979 to 2010 (Parkinson and Cavalieri, 2012a). The modification uses surface temperature from meteorological 70 reanalysis and ice drift from satellite data in order to correct misclassifications caused by melt-refreeze cycles and by snow metamorphosis This has been successfully applied and tested in the Arctic (Ye et al, 2016a, b) and has recently been compared to other sea ice type retrieval results (Ye et al, 2019).
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