This post concerns our paradigm of the Arctic Ocean and its Sea Ice. My view, despite years of watching the waxing and waning of ice extents was subconsciously wrong, and others may share the same misconception.
I owe my enlightenment to a great book by Russian scientists from the Arctic and Antarctic Research Institute (AARI) in St. Petersburg. It’s entitled Climate Change in Eurasian Arctic Shelf Areas, by Ivan Frolov et al. The ebook is behind a paywall, but Dr. Bernaerts graciously provided me a hard copy from his library.
The book is small in volume, but rich in information and insights, so I am taking the time to digest. In reading Chapter 4 I came upon a section entitled: Changes in ice exchange between the Arctic basin, marginal seas and the Greenland Sea. Now I was well aware the export of ice through the Fram Strait and knew of the great 2012 storm that so affected extents that year. But then I read this:
There is extensive sea ice exchange between the Arctic Basin and its marginal seas, which are the major sources of new ice for the Arctic Basin. The Arctic Basin serves as a reservoir for the marginal seas; it both receives large ice masses exported from the seas and supplies the seas with thicker multiyear ice. The direction and intensity of ice exchange depends to a great extent on the wind regime. However, local winds alone do not completely determine this exchange of ice. Ice export from the ice cover of marginal seas depends on sea ice conditions in the central Arctic because the sea ice originating from the marginal seas must have some ability to replace the central Arctic ice cover. Thus, the marginal seas depend to some degree on the intensity of ice export from the Arctic Basin to the Greenland and other subarctic seas. However, ice flow from the basin to the seas during onshore winds is strongly restricted by the shoreline and landfast ice, and ocean circulation also influences this ice exchange.
The Great Arctic Cyclone August 2012
It’s Not an Ice Cap, It’s an Ice Blender
Frolov et al made me realize that all our observations of Arctic ice are in fact snapshots of an ice blender constantly moving ice around the Arctic ocean. When we observe and measure extent in one of the seas, that particular ice was not there previously, and will be gone in the near future, replaced to some extent by ice coming from elsewhere. That is the full implication of Arctic ice lacking a land anchor (like Greenland or Antarctica) and existing as “drift ice”.
Frolov et al. Provide the statistics regarding the annual dynamics. In the wintertime the shelf seas form “fast ice”, that is ice locked onto the coastlines. Additional ice has nowhere to go but go with the flow north toward the pole or to the neighboring sea. In the summer the flow reverses and the Arctic basin, which received ice from the marginal seas, now sends ice back to replace losses there.
Which seas get more ice and which get less ice depends mostly on whether the prevailing circulation is cyclonic or anticyclonic. The diagrams show that where there is a strong low pressure area, a cyclonic air flow develops, which moves water and drift ice in a counter-clockwise direction (seen from above). A strong high-pressure system acts in the opposite direction. I like this image the best, but the labels are in French
Considering the Arctic as a whole, a large-scale cyclone such as the massive one in August 2012, breaks up ice, moves it away from western Russian seas, and flushes great chunks of ice south through the Fram Strait into Greenland Sea where they melt. That storm was exceptional in its strength and size, but storms are always at work in the Arctic, and over multiyear periods, we can observe regimes favoring one or the other type of storm.
Frolov et al. point out:
Recent analyses of wind-driven circulation in the Arctic Ocean show that wind-driven ice motion and upper ocean circulation alternate between anticyclonic and cyclonic regimes. Shifts between regimes occur at 5-year to 7-year intervals, resulting in 10-year to 15-year periods. Based on these analyses, these authors proposed an Arctic Ocean Oscillation (AOO) index showing alternation of the cyclonic and anticyclonic regimes.
Table 4.2. Changes in the ice cover area in August from the beginning to the
end of the circulation cycles in Arctic Ocean regions (in 10^3 km2)
|Circulation regime||Years||North European||Siberian Arctic|
Table 4.2 shows that in 88% of cases during anticyclonic regimes, sea ice extent increases in the North European Basin and decreases in the Siberian Arctic Seas, while cyclonic circulation has the opposite effect. The absolute value of changes in the Siberian Arctic Seas is more than 5 times higher than in the North European Basin.
Frolov et al. Summarize:
An increase in the recurrence of cyclonic pressure fields over the Arctic Basin at the transition from a cooling to a warming epoch leads to changes in ice cover deformation processes. The cyclonic systems of the multiyear ice drift contribute to ice cover divergence. This process is most prevalent in summer, whereas in winter, especially in relatively thin ice zones, ice compacting is usually observed. Anticyclonic SLP fields have the opposite effect.
According to Gudkovich and Nikolayeva (1963), in a year that westerly and southwesterly winds increase over the eastern Barents Sea during October— December, the setup they create in the Kara Sea increases ice export from this sea toward the north. Dominant easterly and northeasterly winds produce the opposite result. This study also shows that ice export from the eastern East Siberian Sea and the southwestern Chukchi Sea during the period considered is strongly influenced by wind field vorticity in the vicinity of Wrangel Island. Anticyclonic vorticity increases the ice export, and cyclonic vorticity results in additional ice flow from the north.
Ice transported through the Fram Strait.
Frolov et al:
Table 4.4. Correlation coefficients between the long period fluctuations of the
area of ice exported through Fram Strait (October-August) and total ice area of the Arctic Seas Asian shelf in August for the period 1931-2000 at different time lags.
|Time lag (years)
As shown in Figure 4.14, ice export fluctuations slightly precede corresponding sea ice extent changes in the Arctic Seas. The cross correlation function between the smoothed values of ice export and total sea ice extent exhibits the highest correlation coefficients at time lags (sea ice extent after export) of 4, 5, and 6 years (Table 4.4). Following decreased ice export through Fram Strait in the early 1990s, a tendency for its increase was observed. Based on the time lags shown in Table 4.4, a transition to the phase of increased sea ice extent in the Arctic Seas would be expected at the beginning of the twenty-first century, as confirmed by Figure 4.14a.
Figure 4.14a shows long-period changes in the total area of ice export through Fram Strait from October of one year to August of the next year for 1931-2000. An approximation of data by a polynomial to the power of 6 (bold curve) indicates the cyclic character of these changes, with the cycle lasting about 60 years. Figure 4.14a shows that the fluctuations of total sea ice extent of the Arctic Seas of the Siberian shelf (from the Kara to the Chukchi Seas) have a similar character.
It is remarkable that increased ice export through Fram Strait is accompanied by increased sea ice extent in the Arctic Seas, contrary to the opinions of those who assume that ice export to the Greenland Sea increases during climate warming, accompanied by a decrease in sea ice extent in the Arctic Seas.
The average drift and current speed in Fram Strait for the preceding year influences the ice exchange between the Arctic Basin and the Laptev, East Siberian, and Chukchi Seas in winter (October—March). The increased ice export to the Greenland Sea contributes to the increased ice export from these seas to the Arctic Basin, and its decrease results in the opposite effect (Gudkovich and Nikolayeva, 1963).
The estimates above show that, on average, about 1 million km2 of the ice cover is transported annually from the Arctic Seas to the Arctic Basin, which is comparable to current estimates of the area of ice exported annually from the Arctic Basin to the Greenland Sea. (e.g., Koesner, 1973; Mironov and Uralov, 1991; Vinje, 1986). Given a typical ice thickness value, we can estimate the volume of ice exported to the Arctic Basin during a winter to be approximately 1500-2000 km3. This value is about half as large as the available estimates of ice export to the Greenland Sea in winter (Vinje and Finnekasa, 1986; Alekseev et al., 1997), which can be accounted for by ice growth, ice ridging, and other processes that occur during transport of the ice to Fram Strait.
It is a mistake to think of the Arctic as an ice cap that shrinks and grows in extent. In fact Arctic ice is constantly in flux, more like a kalidiscope than an solid sheet. And the natural forces within the climate system cause fluctuations on a quasi-60yr oscillation
NASA’s Aqua satellite captured this natural-color image of the storm in the Arctic on August 7, 2012. The storm – which appears as a swirl – is directly over the Arctic in this image. NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response.