Since the mid 1980s, the Arctic sea ice cover has retreated significantly and 2007 saw by far the lowest extent since 1979 [Stroeve, et al., 2008]. However, to consider these changes in a longer-term context, we need to look beyond the satellite record. Here, we present a new observational dataset of sea ice extent in the Russian Arctic. We derive our results from historic Russian sea ice charts that date back to July 1933 and comprise the longest-lived systematic sea ice record in existence. By locating points along the sea ice edge in each chart, we have calculated seasonal mean extents for each marginal sea of the Russian Arctic for both the total ice pack and the multiyear ice component. Figure 1 shows the boundaries of the marginal seas as we defined them in this study. We have also undertaken an extensive error analysis and Figure 2 shows the timeseries of mean summer sea ice extent over the whole Russian Arctic with our error estimates. The complete dataset of seasonal mean ice extents for each marginal sea will be published together with the errors by the National Snow and Ice Data Center. We anticipate that this will be a valuable resource for examination of near-century scale changes in Arctic.

Our results clearly show that the Russian Arctic sea ice cover experienced a general retreat over the chart record and that the current sea ice extent in the Russian Arctic is unprecedented in at least 74 years. However, the retreat has not been constant and the record shows that the retreat in the early part of the record stopped around the 1950s when a partial recovery took place, which continued until the 1970s-80s. Furthermore, when we examine individual seas and seasons (Figure 3) we see that the early period of retreat was only evident in summer and autumn and only in some seas. By contrast the retreat in recent decades can be observed in all seas in summer and autumn and also in winter and spring in the Barents and Laptev Seas. We therefore identify three distinct periods of sea ice variability, which we label Periods A, B and C in chronological order.

Figure 4 shows that multiyear sea ice within the Russian Arctic has experienced the same general pattern of retreat, partial recovery and retreat. However, the different subplots in Figures 3 and 4 reveal variability in the timing of the transitions between periods A, B and C. For this reason, we have deliberately made the boundaries between the three periods fuzzy in Figures 3 and 4. Using a bootstrap technique, we fitted cubic curves to the seasonal data to examine the variability of the transitions between the three alternating periods of variability. This analysis shows that, where periods A and B were both evident, the transition from retreat to recovery occurred between approximately 1947 and 1958. The end of the recovery and onset of the recent retreat is better defined and in more seas and seasons. Our analysis shows the period B/C transition occurred between 1979 and 1985. The alternating pattern of sea ice retreat and recovery is strikingly similar to variability in summertime air temperatures as well as intermediate Atlantic water temperatures [Polyakov et al, 2004] and the Arctic Ocean freshwater anomaly [Polyakov et al., in press]. Further work is required to compare the timings of the transitions in sea ice variability with those of the transitions evident in other records.

The sea ice charts examined here do not provide information outside of the Russian Arctic. However, air temperature records show that the early 20th century retreat in the Russian Arctic coincided with increasing summertime temperatures while the summers in the rest of the Arctic were cooling. This suggests that the Arctic as a whole did not experience the same sea ice retreat as the Russian Arctic during period A. Therefore, although our results indicate a general reduction in sea ice in the Russian Arctic, it seems that the retreat during recent decades is more severe than during the early 20th Century.