Cartographies of the Arctic are powerful instruments to support legal, political, commercial, and scientific claims and interests in the region. Polar projections on sea ice extension, the distribution of natural resources or the state of ocean currents in the Arctic, for example, are critical indicators for the future of the region. At the same time, natural scientific categories to describe the Arctic are products of historical processes in the production of geographical knowledge; they are not eternal givens. As disciplines such as oceanography, meteorology or hydrology emerged as fields of professional study during the nineteenth century, new theoretical and visual vocabularies equipped explorers and cartographers with the language of natural science to relate the regions and their representation in maps to the geopolitical, commercial, and scientific interests of nineteenth-century European and North American states. Grounded in historical data and archival research, this article discusses how such cartographies re-defined the Arctic region, how they generated a surge in Arctic expeditions, and how they continue to inform modern understandings of the region, one predominantly perceived as a region of nature. Specifically, this article discusses the theory of an Open Polar Sea—a body of navigable, ice-free water in the central Arctic Ocean—as a consequential re-envisioning of the central Arctic and a generator of scientific agendas of Arctic exploration across Europe and North America that, in turn, informed contemporary field science such as the recent MOSAiC expedition.