History of the North Sea great herring fishing industry resulting in Scotland becoming a European leader in that industry. During the First Schleswig War (1848–51), the Crimean War (1854–56) and the Second Schleswig War (1864), belligerents took steps to reduce or eliminate commerce in the North Sea by their enemies. In the first Schleswig War, Denmark was able to halt maritime commerce by Germany in the North Sea and in the second, imposed tolls on ships crossing through the Danish straits between the Baltic and North Seas. The Crimean War saw British and French expeditions sent into the Baltic to prevent Russian ships' egress into
North Atlantic Gyre the central role it plays in the thermohaline circulation, bringing salty water west from the Mediterranean Sea and then north to form the North Atlantic Deep Water. The North Atlantic Gyre traps man-made marine debris in the North Atlantic Garbage Patch, similar to how the North Pacific Gyre traps debris in the Great Pacific Garbage Patch. The North Atlantic Gyre forms the Sargasso Sea, noted for its still waters and dense seaweed accumulations. As with many oceanographic patterns, the North Atlantic Gyre experiences seasonal changes. Stramma and Siedler (1988) determined that the gyre expands and contracts with a seasonal variance;