Thursday, 18 July 2019

Another look at Arctic ice - 17 July, 2019

Margo & Robin Take Their 
First Look at Arctic Sea Ice 
for 2019 (July 17, 2019)

Temperatures are above zero throughout the Arctic

We are starting to get areas of ice breaking up at 83-85 
deg N

It is difficult to see what is happening in the high Arctic due to the preponderance of cloud but in places we can see the break-up of ice.

This shows the break-up of ice at 83N and shows signs of meltpools

A lot of melting to the north of Severnaya Zemluya in the Laptev Sea

Here some highlights from Natalia Shakhova et. al. latest paper that confirms a lot of what we have observed or inferred by observation

Increasing periods of open water implies an increasing number of storm events, when wind speed increases to ≥15 m s−1 and the boundary between sea surface and air increases many fold due to deep water mixing. Such events have the potential to rapidly ventilate bubble-transported and dissolved CH4 from the water column, producing high emission rates to the atmosphere. Because >75% of the total ESAS area is <50 m in depth, the water column provides bubbles with a very short conduit to the atmosphere. Storms enable more CH4 release because they destroy shallow water stratification and increase the boundary between sea surface and air, thus increasing gas exchange across phase boundaries. As a result, storm-induced CH4 “pulses” force a greater fraction of CH4 to bypass aqueous microbial filters and reach the atmosphere [20].

In addition, about 10% of the ESAS remains open water in winter due to formation of flaw polynyas. Formed simultaneously with land-fast ice in November, flaw polynyas propagate out of fast ice hundreds of kilometers north [82]. Flaw polynyas provide pathways for CH4 escape to the atmosphere during the arctic winter [17]. Areas of flaw polynyas in the ESAS increased dramatically (by up to five times) during the last decades [83], and now exceed the total area of Siberian wetlands [84] (Figure 7). This implies that the ESAS remains an active source of CH4 to the atmosphere year-round, even in the winter when terrestrial Arctic systems are dormant. Increasing storminess and rapid sea-ice retreat causing increased CH4 fluxes from the ESAS are possibly new climate-change-driven processes.

Continuing warming of the AO will strengthen these processes, and the role of the ESAS as a year-round contributor to global CH4 emissions will grow over time. The ESAS is a tectonically and seismically active area of the WO [85,86]. During seismic events, a large amount of over-pressurized gas can be delivered to the water column, not only via existing gas migration pathways, but also through permafrost breaks that can occur within otherwise continuous permafrost or pingo-like structures observed over the Arctic shelf [73].

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