Nils Otto Gustaf Nordenskjöld (December 6, 1869 – June 2, 1928) was a Finnish and Swedish geologist, geographer, and polar explorer.
Nordenskjöld was born in Hässleby in Småland in eastern Sweden, in a Finland Swedish family that included his maternal uncle, polar explorer Adolf Erik Nordenskiöld, and cousin Gustaf Nordenskiöld. His father and mother were cousins, but his father's family name was "Nordenskjöld", while his mother's family name was spelled "Nordenskiöld".
He studied at Uppsala University, obtaining a doctorate in geology in 1894, and later became a lecturer and then associate professor in the university's geology department.
Otto Nordenskjöld led mineralogical expeditions to Patagonia in the 1890s, and to Alaska and the Klondike area in 1898.
He led the 1901-1904 Swedish Antarctic Expedition, aboard the ship Antarctic. The expedition visited the Falkland Islands before the ship, commanded by seasoned Antarctic sailor Carl Anton Larsen, dropped Nordenskjöld's party off at Snow Hill Island, a small island off the coast of the Antarctic Peninsula. Nordenskiöld overwintered at Snow Hill Island, while Antarctic returned to the Falklands. The following summer Larsen brought her south, intending to retrieve the Nordenskiöld party, but she became trapped in ice which eventually crushed her hull, forcing Larsen and his crew to overwinter in a hastily constructed shelter on Paulet Island. Larsen and Nordenskjöld finally rendezvoused at their fall-back rescue hut at Hope Bay in late 1903, where they were picked up by the Argentine Navy corvette ARA Uruguay (commanded by Julián Irízar), which had been dispatched when Antarctic had failed to make her appointed return to South America the previous year. Despite its end and the great hardships endured, the expedition was considered a scientific success, with the parties having explored much of the eastern coast of Graham Land, including Cape Longing, James Ross Island, the Joinville Island group, and the Palmer Archipelago. The expedition, which also recovered valuable geological samples and samples of marine animals, earned Nordenskjöld lasting fame at home, but its huge cost left him greatly in debt.