Overland links to Europe are most of it. If you look at the number of major Russian ISPs that are members of the DE-CIX in Frankfurt, that's a good indicator of traffic flows.
The lack of land connections on the map threw me for a loop, too; it makes it look like there are no direct connections between North America and Iceland (or Greenland, for that matter) due to the apparent gaps where there are (hopefully) overland cables.
Is it really so, or is data missing from the map? Anyone know the reason why?