vox_mundi posted a more complete report in the 2021 Melt Season thread, but here is the gist of a new study:
from
https://phys.org/news/2021-04-arctic-sea-ice.html "...plumes of warm water are flowing into the Arctic Ocean from the Pacific Ocean and accelerating sea ice melt from below."
"Most oceans of the world have warmer, lighter water near the surface and colder, denser water below. In the Arctic, however, there is a surface layer that is cold but very fresh, influenced by river outflow and accelerating ice melt. Warm, relatively salty water enters from the Pacific Ocean through the Bering Strait"
"Because this water is saltier than the Arctic surface water, it is dense enough to "subduct," or dive beneath, the fresh Arctic surface layer. Its movement creates pockets of very warm water that lurk below surface waters. Scientists have been seeing these pockets of warm sub-surface water strengthen over the last decade."
From the open access journal article
"A warm jet in a cold ocean" by MacKinnon et al.
https://www.nature.com/articles/s41467-021-22505-5 This Pacific Summer Water (PSW) "...is typically found 30–100 m below the surface, frequently in the form of patchy eddies and filaments"
"In the short term, the fate of subducted heat may impact the timing of sea ice growth in late autumn, if it remains close enough to the surface to be rapidly mixed upwards by strong fall storms"
"Observations show that the heat content of the sub-surface PSW within the BG (ed. Beaufort Gyre) has nearly doubled over the last 30 years.
If all this heat were turbulently mixed upwards, it could melt more than a meter of sea ice."
"As the heat content of PSW is growing, the combination of PSW subduction, lateral stirring, and upward vertical mixing should lead to a pattern of accelerating sea ice melt spreading out from the Pacific inflow, as has been observed in recent decades.
Related processes have been observed on the other side of the Arctic, associated with warming of subducted Atlantic water". (ed. bolding added)
"At the same time, the BG is spinning up, with a growing accumulation of near-surface freshwater ... as the PSW warms and lightens ...it is subducting along shallower isopycnals, putting it closer to the surface." (ed. isopycnal = line connecting points of a specific density, like the isobars on an atmospheric pressure map)
2 min 44 sec video:
FWIW: My interpretation (caveat - the technical details of the article are beyond my scope):
Bad news for the ASI. Based on estimated ice thickness in the Beaufort Sea in Sept. 2020, the observation that there is already enough submerged heat to melt another meter of ice, and that the warm PSW intrusion continues, is probably increasing, and is getting closer to the surface, suggests that the Beaufort will soon routinely become ice-free during September (see Wipneus PIOMAS graphs below showing extent of <=1 meter thick ice).
With August and October ASI thickness not much different from September, continuation and speculated strengthening of the PSW heat influx would expand the onset and duration of the Beaufort ice-free period into August and October within a few years after the Beaufort begins routinely melting out in September.
