Weather data contained in American whaling voyage logbooks and other archival documentation is used to assess historic changes in the climate and weather patterns of the Indian Ocean. The recording of atmospheric conditions in the nautical context was essential: to travel safely, mariners needed to record and compile weather data. The logbooks thus contain systematic weather observations (e.g., wind strength/direction, storms, precipitation, surface air temperature, pressure) at daily to sub-daily temporal resolution. We focus on unexploited caches of archival documentation, namely American whaling logbooks of voyages to the Indian Ocean (ca. 1785-1910) in New England archives housed by the New Bedford Whaling Museum and the Nantucket Historical Association (Massachusetts, USA). The project is predicated on historical climate data rescue and recovery through the extraction of data from under-used archived documentation, and advocating and facilitating the digitalisation of such materials.

Long-term changes in strength and position of the Southern Hemisphere westerlies since the late 1800s are explored, as well as changes in characteristics of the Mascarene subtropical high pressure system in the southern Indian Ocean and associated circulation regimes. The historic records provide an important long-term context for the rapid changes in extratropical wind patterns in remote regions of the Southern Hemisphere observed in recent decades. Potential for a citizen science component for this research is discussed as well.