In particular marginal Seas
such as the Baltic Sea, the second largest brackish water area in the world, are affected.
For Spykman, dominating such marginal seas is crucial to projecting power into the Eurasian rimlands and thence into the vast interior.
Circumventing this marginal sea imposes significant costs in terms of extra fuel, wear and tear on equipment, and crew fatigue, but such challenges are manageable compared to rounding South America or Africa.
During the interglacial period, the sea level rose and the land bridges disappeared, thereby interconnecting previously isolated marginal seas and facilitating dispersal over vast geographical ranges (Liu et al.
Pleistocene isolation in the northwestern Pacific marginal seas and limited dispersal in a marine fish, Chelon haematocheilus (Temminck and Schlegel, 1845).
This effect is far more direct and immediate in enclosed or marginal seas, where in many cases the loss of sea control can lead to the collapse of one's front on land and thereby considerably affect the outcome of the war.
A fleet operating in one or more enclosed or marginal seas might opt for, or be forced by circumstances to accomplish, a combination of objectives--general sea control in the enclosed sea theater, and contested control in a semi-enclosed sea or parts of the adjacent oceans.
Commercially viable fishing has continued in the Arctic marginal seas, and a total collapse of any single fishery has been averted using stringent harvesting quotas and other bilateral agreements.
Greenhouse gas emissions have been unleashed globally at unprecedented rates; the result has been massive permafrost thawing (and disappearance), rapid glacial retreat in Greenland and Canada, extensive coastal shore erosion, and a historic retreat of Arctic sea ice in all marginal seas and the central Arctic Ocean.
Various dense overflows from marginal seas
such as the Mediterranean are even smaller, 1 to 3 million cubic meters per second.
Most, if not all, fossil oceanic crust on land is now believed to be atypical, formed in young rifts, around island arcs, and in marginal seas
above subduction zones.