Short answers, pulled from the story.
The Kara Sea is a marginal sea of the Arctic Ocean lying north of Siberia. It is separated from the Barents Sea to the west by the Kara Strait and Novaya Zemlya, and from the Laptev Sea to the east by the Severnaya Zemlya archipelago.
The Kara Sea is roughly 1,450 kilometers long and 970 kilometers wide, with an area of around 880,000 square kilometers. Its mean depth is 110 meters.
The Kara Sea is named after the Kara river, which flows into Baydaratskaya Bay and played an important role in the Russian conquest of northern Siberia. The river's name derives from a Nenets word meaning hummocked ice.
Finnish explorer Adolf Erik Nordenskiöld became the first to force the Northeast Passage. In 1878 he sailed the Vega from Gothenburg across the Kara Sea and along the Siberian coast, wintered frozen in the Chukchi Sea, and reached Yokohama, Japan the following year.
Between 1965 and 1988 the Soviet Union dumped six nuclear submarine reactors and ten nuclear reactors into the Kara Sea, according to a Russian government White Paper released in March 1993. The dumped material also includes the scuttled submarine K-27, whose two reactors still contain spent nuclear fuel.
The Kara Sea contains the East-Prinovozemelsky field, an extension of the West Siberian Oil Basin, holding significant undeveloped petroleum and natural gas. In October 2010 the Russian government licensed Rosneft to develop the structure, and in 2014 US sanctions gave Exxon until the 26th of September to halt its operations there.
In 1912 unbroken consolidated ice blocked the Northern Sea Route and trapped three Russian expeditions, all of which failed: Sedov's St. Foka, Brusilov's St. Anna, and Rusanov's Gercules. Sedov later died on Rudolf Island, only two men survived the St. Anna ordeal, and Rusanov's expedition was lost entirely.