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Topics - SATire

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Arctic sea ice / Year-round ice-free Arctic
« on: April 03, 2013, 01:53:11 PM »
After reading other threads in this forum and Neven's blogs I assume some agreement about the prediction of an ice-free arctic in summer between this year and 2017 (e.g. caused by exponential decline of ice volume due to albedo-feedback, I also assume some agreement from climate paleontology, that current atmospheric CO2 content of 400 ppm is similar to the Pliocene or even Miocene situation. Therefore, we are now in a transition period from (inter-)glacial clima to a glacial free clima at least in northern hemisphere. What is unclear and of interest are the major processes driving this transition and their time scale. I would like to describe a possible process for the transition to a year-round ice-free arctic basin below.

If you read this, please be aware, that I am not a climate specialist nor a ocean scientist. I am only an interested amateur in this field (instead I am an engineer with a PhD in physics, for the case you want to know that). But since the professionals are failing so badly predicting current situation in the arctis for 2050 using history-proofed complex models, we all have a chance to do better even with simple empirical pictures. So I am interested in your critics and thoughts, maybe we can find a proper description of probable transition schemes together.

As introduction I would like to point to an article describing the waters and the halocline in the arctic ocean very nicely und readable:
In figure 1 in that paper you find salinity- and temperature profiles in the Eurasian basins (Nansen basin (yellow) and Amundsen basin (green)), the Makarov basin in the center of the arctis (violet) and the Canada basin next to Alaska (blue). Some possible origins of the haloclines there are described quite understandable.

In the Eurasian basin below a depth of ~100m warm waters of atlantic origin are hold back by the halocline. Since the halocline is a result of sea-ice e.g. north of Svalbard and in Barents sea, an ice-free arctic can result in a slow "atlantification" of the arctis. An absence of a halocline in the Eurasian basin would result in a mixing with deeper warm waters preventing the formation of ice in winter.

An additional mechanism able to destroy the halocline could be vaporization of water over an ice-free Eurasian basin in autumn: Since the salinity is only 1 PSU lower in the top 100 m (yellow curve for Nansen basin) and 1 PSU is 0.1% salt content, only 10 cm of water need to be vaporized to result in disappearing halocline there (0.1% x 100 m = 0.1 m) after some mixing. The heat needed to vaporize this water has to be stored in the upper water layer, e.g. the top 10 m. Since 2700 kJ/kg are needed (2256 kJ/kg vaporization enthalpy + 420 kJ/kg for 0->100 °C), for comparison that is the energy needed to melt 0.8 m ice (334 kJ/kg) or to heat a 10 m water culumn by 6.4 °C. I think that amount of heating is well in reach for an ice-free ocean in the summer.

In the Amundsen Basin this numbers would be 0.15 m to vaporize (0.15% x 100m, heat equal to 10 m water heated by 10 °C), in Makarov basin 0.3m (2 PSU x 150 m) and in the Canada basin 1 m (8 PSU x 50 m plus 3 PSU x 200 m). Therefore, I estimate the transition time to an all-year ice-free ocean 1-2 years for the Eurasian basin and 1-2 decades for the Canada basin. Both transitions would start after the ice melted early enough to result in a surface temperature of 5-8 °C  (7-10 °C above melting temperature there).

To conclude, I have drawn a picture to describe how and when evaporation could result in a perennial ice-free state above the deep basins in the arcits and I am asking for your thoughts. This is not a proper prediction for the bays (e.g. Hudson) and the shelf waters (Siberian seas, Kara, Tschuktschen, Makenzie delta,...) - I think some ice will be grown in that areas under the influence of fresh-water inflow and cold air from continents.

Since open sea in the arctis will kill the polar vortex, the jet stream and the atmospheric flux of energy to the arctis the oceans currents must cool the equator on the long run. Evaporation will suck the Atlantic water north and cover the continents with a ton of wet snow. The persistent depression over the artic ocean will kill the jet stream and the westerlies - leaving only the Antarctis to cool the Equator by air. What would that mean for monsuns, westerly, northern trade wind, ... persistent winter weirdness globaly, I guess. 
And what would that mean to Greendlands ice -  that last memory of the glacial periode? Probably some more water to motivate our dykers.
Erratum: Since the change of salinity by vaporization is calculated wrong in this message (see comment from Peter Ellis below), vaporization is not reasonable to destroy the halocline. Instead other processes could be discussed in this thread. I am sorry for that mistake.

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