Nice combo! Might think about cropping off lower Greenland, looks like there is room for 2x the inset resolution. That consistent spike at 50% suggests a round-off bias. Or, if you are taking pixel counts off the grayscale, that conversion could also do it if there is a palette collision on fairly uncommon concentration classes.
Found some more open water papers. The first distinguishes between 'ice albedo effect' (much discussed on forums) and 'ice-ocean albedo effect' (my current interest) which focuses on dominant lower albedo of open water and the non-radiation of sunlight back out to space.
Cumulative solar adsorption by a small patch of open water on May 20th in the Chukchi really starts to add up after fourteen weeks (September), as do ice-free Bering Kara and Barents seas which also affect the Arctic basin, compared to a big patch opening up in mid-August at 80ºN which barely gets a couple of weeks of post peak solstice insolation. (Multiply area under the surface insolation curve by sq km of open water to get 20:1 effect.)
Evidence for ice-ocean albedo feedback in the Arctic Ocean shifting to a seasonal ice zone
H Kashiwase, K Ohshima, S Nihashi & H Eicken
Scientific Reports v7 8170 (2017)
https://www.nature.com/articles/s41598-017-08467-z"Ice-albedo feedback due to the albedo contrast between water and ice is a major factor in seasonal sea ice retreat, and has received increasing attention with the Arctic Ocean shifting to a seasonal ice cover. However, quantitative evaluation of such feedbacks is still insufficient.
"Here we provide quantitative evidence that heat input through the open water fraction is the primary driver of seasonal and inter-annual variations in Arctic sea ice retreat. Divergent ice motion in early melt season triggers large-scale feedback which subsequently amplifies summer sea ice anomalies; divergence has doubled since 2000 due to a more mobile ice cover.
"Until recently, the Arctic Ocean has been characterized by a thick multiyear ice cover that persisted throughout the summer, with melt confined to its upper surface. In the seasonal ice zone, presence of an open water fraction with a much lower albedo results in high solar radiation absorption by the upper ocean which in turn serves as the dominant heat source for sea ice lateral and bottom melt. Since the seasonal ice zone is dominated by thin and undeformed first-year ice, the melting of sea ice immediately increases the fraction of open water in the ice-covered area and thus ice-ocean albedo feedback drives up absorption of solar energy in the upper ocean.
"Here we show the dominance of heat input through the open water fraction on sea ice loss We selected the Pacific Arctic Sector (fan-shaped area in figure) as the main study area. This region experienced the largest reductions in summer ice extent and volume anywhere in the Arctic Ocean beginning in the 2000s. Inter-annual variation of ice retreat in this region explains about 86% of the variance over the entire Arctic Ocean (p < 0.001).
Dominance of heat input through the open water fraction: "For the ice-covered area defined by ice concentrations >15%, we have analyzed the daily heat budget separately for the water and ice surfaces from 1979 to 2014. During the summer season, net heat flux at the water surface is much larger than that at the ice surface because shortwave radiation is the dominant component of heat budget in the analysis area…
"The fraction of multiyear ice based on ice age data has decreased from 49 to 31%. This reduction affects sea ice dynamics, in particular through decreases in ice mechanical strength and internal ice interaction forces, and increases in ice deformation rates
"Other factors such as changes in atmospheric circulation patterns, influence of cloud cover, long wave radiative forcing due to anthropogenic CO2 emission, melt pond distribution in the early summer season, release of the solar heat stored in a near-surface layer of the ocean, and increases in the heat inflow through Bering Strait may also contribute to drastic ice reductions. However, we note that these factors are intrinsically linked to divergence in the ice pack, because increased heat input from any source may enhance sea ice mobility.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JD023712Yet another reason
not to use DMI 80: "The European ERA‐Interim reanalysis data and NCEP‐CFSv2 analysis data are used to investigate the surface energy budget and atmospheric conditions in 2012 and 2013. The ERA‐Interim reanalysis data are the latest global atmospheric reanalysis produced by the ECMWF is available from 1989 onward The ERA‐Interim reanalysis routines provide
major improvements compared with ERA‐40 such as better vertical consistency of the air temperature in the Arctic region and an improved representation of the hydrological cycle.
"The open water fraction is typically small (often less than 10%), but the fact that open water absorbs 2 to 3 times as much broadband solar radiation as bare ice means that these small areas can contribute significantly to the overall uptake of solar radiation in the region. Changes that increase the amount of melt, such as an earlier melt onset, will lead to thinner ice that can more easily allow the dynamic formation of leads or be completely melted through.
"The
conditions in 2012 exhibited a longer and more continuous period of ice and snowmelt, with earlier melt onset and later freeze‐up than in 2013, resulting in more ice melt in 2012 than in 2013 [see Perovich 2014a].
"The earlier melt onset in 2012 likely preconditioned the system to allow a longer melt season with lower albedo, resulting in much more solar heat input to the ice‐ocean system in 2012 than in 2013. This additional deposited solar energy would melt the surface, thin the ice, and warm the upper ocean, resulting in more melting and longer melt period. This enhances the positive ice‐albedo feedback."