Changes in the annual sea ice freeze-thaw cycle in the Arctic Ocean from 2001 to 2018

• Main Authors: Lin, Long, Lei, Ruibo, Hoppmann, Mario, Perovich, Donald K., He, Hailun
• Format: Text
• Language: English
• Published: 2022
• Subjects: Arctic; Arctic Ocean; Climate change; Sea ice
• Online Access: https://doi.org/10.5194/tc-2022-137; https://tc.copernicus.org/preprints/tc-2022-137/

The annual sea ice freeze-thaw cycle plays a crucial role in the Arctic atmosphere-ice-ocean system, regulating the seasonal energy balance of sea ice and the underlying surface ocean. Previous studies of the sea ice freeze-thaw cycle were often based on limited accessible in situ or easily available remotely sensed observations from surface. To better understand the responses of the sea ice to climate change and its coupling to the upper ocean, we combine measurements of the ice surface and bottom using multisource data to investigate the temporal and spatial variations in the freeze-thaw cycle of Arctic sea ice. Observations by 69 sea ice mass balance buoys (IMBs) collected from 2001 to 2018 revealed that the average ice basal melt onset in the Beaufort Gyre occurred on 23 May (±6 d), approximately 17 days earlier than the surface melt onset. And the average ice basal melt onset in the Central Arctic Ocean occurred on 17 June (±9 d), which was comparable with the surface melt onset. This inconsistency was mainly attributed to the difference in the seasonal variations of oceanic heat available to sea ice melt between the two regions. The overall average onset of basal ice growth of the pan Arctic Ocean occurred on 14 November, lagging approximately 3 months behind the surface freeze onset. This temporal delay was caused by a combination of the heat released from sea ice cooling, a heat flux from the ocean mixed layer and subsurface layer, as well as the thermal buffering of snow atop the ice. In the Beaufort Gyre region, both (Lagrangian) IMB observations (2001–2018) and (Eulerian) moored upward looking sonar (ULS) observations (2003–2018) revealed an earlier trend for basal melt onset, mainly linked to earlier warming of surface ocean. An earlier trend of basal ice growth was also identified from the IMB observations (multiyear ice), which we attributed to the overall reduction of ice thickness. In contrast, a delayed trend of basal ice growth was identified from the ULS observations, which was explained by ...