Another entry in the dying Earth/Sun or Last Civilization approach is The Phoenix in Obsidian aka The Silver Warriors from 1970 by the oft forgotten but quite seminal Micheal Moorcock of Elric fame, but He wrote way more than that. Set in a frozen Earth and with a Sun that is just a white dwarf. The last surviving sea is so salty and dense is gelatinous and ship actually "flap" over it. It's part of the John Daker/Ereköse series, and in turn part of the bigger inter-books Moorcokian Multiverse.