Surface water temperatures across the Great Lakes and connecting waters in 1965 determined using a ship engineer’s log onboard the SS Bayton

Background: The Great Lakes are undergoing climate change resulting in the predicted loss of winter ice cover and limited data available for assessing model predictions of future changes due to climate change ((Xenopoulos et al., 2024). Limited historical data sets of water temperature are available from water treatment facilities but these reflect nearshore temperatures only. Satellite imagery using Advanced Very High Resolution Radiometry (AVHRR) of sea surface temperature in the Great Lakes began in 1992. Therefore, any earlier pelagic surface water temperature data, such as this dataset, is valuable for establishing models of water temperature changes in the Great Lakes due to climate change. Algoma University (Sault Ste Marie, Ontario) contains an archive of Great Lakes ship captain and engineer logs dating from the 1930s. One log, that of the SS. Bayton, contains seemingly accurate water intake temperatures recorded routinely in the engineer’s log during transit and in port. Archive: The log is a complete record of voyages by the SS Bayton throughout the Great Lakes and St Lawrence River dating from April 18 to December 1, 1965. The gap in the record between June 28 and July 8, 1965 was due to quarantine in Port Colborne, ON. The engineer recorded surface water temperature measurements in Fahrenheit at 4-hour intervals while in transit across lakes, rivers and canals. Data sheets: The “Georeferenced time-stamped surface water temperature across the Great Lakes (April to December, 1965) - Master sheet” file is a digitized version of the engineers log. It contains a summary of dates, times, transects (departure and arrival points), and surface water temperatures directly copied from the log. This data was used to calculate distance (nautical miles), duration (hours), and speed over ground (SOG, knots) for each transect. Between departure and arrival points, surface water temperature measurements were made at 4-hour intervals, recorded as “Counter@” or “Counter temp press” in the “Place end” column of the file. The latitudes and longitudes of surface water temperature measurements were estimated using the distance, duration, and speed over ground calculations. The “Decimal lat long date and surface temperatures across the Great Lakes and St Lawrence River, April to December 1965” file is a summary of the “Georeferenced time-stamped surface water temperature across the Great Lakes (April to December, 1965) - Master sheet” file. It contains day of year (DOY, 1965), time (decimal year), and decimal latitude and longitude for each surface water temperature measurement. Reference cited: Xenopoulos, M., Twiss, M., & Child, M. 2025. Great Lakes Winter Science: Summary Report. A report submitted to the International Joint Commission (IJC) Great Lakes Science Advisory Board, IJC-Great Lakes Regional Office, Windsor, Ontario. https://ijc.org/sites/default/files/SAB_WinterScienceReport_2025.pdf