Modulation of the ice extent in Kara

Natural variability, such as that associated with the AMO and NAO, and other circulation patterns, has and will continue to have strong impacts on the Arctic sea-ice cover. Links between altered ocean heat transport and observed ice loss remain to be resolved, as does the attribution of these transport changes, but pulses such as those currently poised to enter the Arctic Ocean from the Atlantic could provide a trigger for a rapid transition. We are not yet capable of predicting exactly when the AMO will switch, in any deterministic sense. Computer models, such as those that predict El Niño, are far from being able to do this. What it is possible to do at present is to calculate the probability that a change in the AMO will occur within a given future time frame. Probabilistic projections of this kind may prove to be very useful for long-term planning in climate sensitive applications. In this respect the wavelet tools might be useful to trace the short-term climate fluctuations of various scales. We used reconstructed time series of ice extent in Russian shelf seas for last century (Polyakov and Johnson 2000; Polyakov et al. 2003). Smoothed curve (Fig. 2) demonstrated 60 years natural oscillation scale, which is similar with similar Atlantic SST (Fig. 1). One can found mutual consistency of both curves. Positive SST anomalies correspond to negative deviations in the ice extent, but with some delay in first half of last century. Figure 1 demonstrated 20 years staying in positive phase during 19401960. Corresponding transition in the ice extent to a positive phase started after 18 years staying in negative phase (Fig. 2). It was due to a growing anthropogenic

Fig. 1. An averaged North Atlantic SST (°C) - AMO nonlinear and linear trend for January: 1900-2000.
Arctic Sea Ice Decline From 1900 1940

1900 1910 1920 1930 1940 1950 1960 1970

year

Fig. 2. Nonlinear and linear trend for Kara Sea ice extent anomaly (10 km ) anomalies: August: 1900-2000.

1900 1910 1920 1930 1940 1950 1960 1970

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1990 2000

Fig. 2. Nonlinear and linear trend for Kara Sea ice extent anomaly (10 km ) anomalies: August: 1900-2000.

Atlantic Multidecadal Oscillation: Wavelet Power Spectrum, log2(power)

Atlantic Multidecadal Oscillation: Wavelet Power Spectrum, log2(power)

Time (year)

Kara Sea Ice Extent (August): Wavelet Power Spectrum (log2)

Kara Sea Ice Extent (August): Wavelet Power Spectrum (log2)

Wavelet Power Spectrum
Fig. 3. Coherency in wavelet power spectrum (log2 scale) for climate series of: AMO winter values for 1856-2000 (upper panel) and ice extent September values in Kara Sea for 1900-2000 (lower panel).

factor. These periodicities might be found independently by wavelet analysis of both time series. The ice extent wavelet power spectrum (Fig. 3, lower panel) and its comparison with the AMO wavelet spectrum (Fig. 3, upper panel) confirm this important conclusion. Thus, it is the North Atlantic water temperature that is a major regulator of the ice extent in the Kara Sea. A similar result was obtained for the Barents Sea, but the ice extent values there were much lower and respective variability was in contrast higher. Moreover, its opposite phases are a physically evident and explainable phenomenon. Ice extent modulation gives an additional argument in favor of hypothesis that Atlantic waters are major contributor in Eastern Arctic ice melting during last decades.

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