Melt Onset of Arctic and Antarctic Sea Ice from Scatterometer Data

The melt onset (MO) of sea ice plays a crucial role in the polar climate system and is detectable by satellite remote sensing. This study used scatterometer data to identify the melt onset dates of Arctic and Antarctic sea ice. The MO identified by this method primarily reflects early changes in the physical properties of the snow layer and is therefore usually earlier than the melt signals detected based on sea ice concentration data. Results show that the melt onset dates in both polar regions exhibit a clear latitudinal dependence. During the study period (2007-2022), no statistically significant long-term trends were found in the average MO for the entire Arctic or for any of its sub-regions. Instead, interannual variability dominates the temporal evolution of MO in the Arctic. Similarly, most Antarctic sub-regions show no significant trends, with the notable exception of the Ross Sea, where MO has advanced significantly. This study further analyzed the trends in the Arctic surface energy budget based on multiple time windows. The net surface energy flux shows a consistent and statistically significant increase only in the Bering Sea across all considered time windows, which supports the earlier MO observed in this region. Although the advance in MO in the Bering Sea does not reach statistical significance, its magnitude (-3 days/decade) is substantially larger than that in most other sub-regions. Following the pronounced decline in Arctic sea ice extent that began in 2007, the trend of advancing MO has not been statistically significant. The underlying mechanisms driving this recent change warrant further investigation.