- "As soon as you get on his ships, they're gonna slit your throats and dump your bodies to the bottom of the Shivering Sea!"
The Shivering Sea is a substantial ocean located to the northeast of Westeros and north of Essos in the Known World. It separates Essos from the northern polar icecap. The Narrow Sea opens into the Shivering Sea just east of the Vale of Arryn. The entire eastern coast of the North is on this ocean: the Bite and the Bay of Seals are inlets of the Shivering Sea.
In the books
In the A Song of Ice and Fire novels, the Shivering Sea is an immense polar sea. Its northernmost reaches are frozen, filled with dangerous icebergs, and unexplored. It might not entirely circle the pole, as the northernmost limits of Westeros's landmass beyond the Wall are uncharted. The west coast of the lands beyond the Wall in Westeros, such as around the Bay of Ice, are not actually considered to be a continuation of the Shivering Sea but an extension of the Sunset Sea.
The largest island on the sea is Ib, located almost three thousand miles due east of Skagos. Ibben is home to folk who make their trade from fishing and whaling, selling their catches in the Free Cities and the ports of northeastern Westeros. It is the second largest island in the known world, behind only Great Moraq in the Jade Sea. Ibben is located about as far east as Vaes Dothrak and Qarth in mainland Essos, but around the same latitude as Winterfell and the Wall in Westeros.
The Shivering Sea becomes extremely dangerous to cross during winter, due to severe storms and also to icebergs and other cold-weather dangers. The northernmost parts - roughly starting at the same latitude as the Wall in Westeros - are dangerous and filled with sea ice, but south of this the Shivering Sea is rich with fish and whales.
The western reaches of the Shivering Sea are the richest fishing grounds in the known world: roughly a triangle from where it joins the Narrow Sea between Braavos and the Vale, up the west coast of Westeros (including the Bite and the Three Sisters) to around Skagos and he eastern end of the Wall, and east to around the mouth of the Sarne River (a sizable distance east of Lorath, roughly at the same line of longitude as the western side of Slaver's Bay). These western waters are plied by large fishing fleets from both Westeros and Essos, though they are generally dominated by the fleet of Braavos. Lorath is much weaker than Braavos and only exerts control over is home waters. Ibbenese fishing flees are also always pushing west, and squabbles over access to bountiful fishing grounds far away from sight of land have led to innumerable minor wars between these different powers over the centuries.
The Dothraki Sea forms much of the north coast of Essos on the Shivering Sea, but because the Dothraki hate and fear the oceans (not trusting any water a horse won't drink), they have no ships or presence at sea whatsoever. As a result, the Ibbenese rule every rock and shoal in the Shivering Sea without opposition - that is, east of where Braavos and Lorath's presence at sea ends at the mouth of the Sarne. These wateres are not as fabulously bountiful with fish as the regions west of the Sarne, but they are still quite plentiful in fish, crabs, lobsters of monstrous size, walruses, and whales. The Ibbense are most famous for their whaling industry, with their great whaling ships carrying oil to many of the major ports in the Narrow Sea. Their influence extends all the way east to the Thousand Islands, which are on the north side of Essos from Yi Ti. The Thousand Islands are inhabited by savage natives who shun the sea, and the fish from the surrounding waters are mishappen with a bitter, unpleasant taste, so after charting them the Ibbenese do not regularly sail there and do not venture father east, beyond the edge of the known world.
The fact that the western end of the Shivering Sea, where it meets the Narrow Sea, contains the richest fishing grounds in the world actually seems to be based on real life principles about fishing patterns. The best ocean zones for aquatic plant life (particularly free floating sea plankton) to grow are in warm waters near Earth's equator that get the most sunshine - but conversely, the best ocean zones for aquatic animals to live in are in cold waters. Due to certain chemical and physical properties, cold water actually retains much higher levels of oxygen than warm water: therefore, fish that live in colder waters need to expend less energy to breathe the same amount of oxygen through their gills. Sea mammals such as whales and dolphins of course breathe air, but they are dependent on fish for food, so they thrive wherever fish are thriving. In isolation, however, cold water zones don't have as much plankton for fish to eat. As a result, the absolute best fishing grounds are in cold water zones in upper latitudes where ocean currents carry plankton up from the warmer water zones where aquatic plants thrive. For example, the Gulf Stream carries plankton up from the Gulf of Mexico to the colder waters of the North Atlantic, so fish in those cold waters can both breathe more easily and have abundant plankton to eat, forming a rich belt of fishing grounds from Maine to Norway (similar effects also make abundant fishing grounds around Japan and Alaska).
The known world
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