Multidecadal variability in the Arctic/North Atlantic climate system

Atmospheric and oceanic variability in the Arctic shows the existence of several oscillatory modes. The decadal-scale mode associated with the Arctic Oscillation (AO) and a low-frequency oscillation (LFO) with an approximate time scale of 60-80 years, are dominant. Both modes were positive in the 1990s, signifying a prolonged phase of anomalously low atmospheric sea level pressure and above normal surface air temperature in the central Arctic.

Consistent with an enhanced cyclonic component, the arctic anticyclone was weakened in the late 1980s - 1990s when the air pressure high in western Arctic was decreased (less red color in Figure 1) and the air pressure rises over the Icelandic Low (more blue color) extending farther into the Barents and Kara seas.

The particularly rapid reduction of arctic ice thickness in the 1990s may be one manifestation of the intense atmosphere and ice cyclonic circulation regime. Using a coupled ice-ocean model, we demonstrated that cyclonic winds flush multiyear ice from the central Arctic resulting in numerous openings in the ice cover. Repetition of this process over several years resulted in thinner ice in the central Arctic and thicker ice along its peripheries (Figure 2, below).

That is why during positive, cyclonic LFO epochs (i.e. in the 1940s through early 1950s and in the 1980-1990s) the observed and simulated arctic sea ice was thinner (Figure 3, below).

Our results also suggest that the decadal and multidecadal modes drive large amplitude natural variability in the Arctic making detection of possible long-term trends induced by greenhouse gas warming most difficult.

Simulated long-term variability of arctic ice thickness and concentration, surface water salinity and temperature, and sea level is shown in the movies. Choose from the links below to view a movies of the variables indicated.

• Salinity and Temperature
• Ice Thickness and Ice Concentration
• Sea Level