He was then appointed professor, by royal decree on the 5 December 1884, and was simultaneously made curator of the new "Department of Archegoniates and Fossil Plants" at the Swedish Museum of Natural History.
Nathorst visited Spitsbergen in 1870 and in 1882–83 he participated in the Second Dickson expedition ("Den andra Dicksonska Expeditionen till Grönland"[2]) led by Adolf Erik Nordenskiöld.
He led an expedition on the ship Antarctic to Bear Island and Svalbard including the isolated Kong Karls Land in 1898.
Starting with macrofossil deposited in glacial clay found in Scania in 1871, Nathorst investigated postglacial development in plants.
He also researched plant remains from older geological eras, such as the palaeozoic and mesozoic from the Arctic and tertiary from Japan.