Assessment of early 20th Century climate model simulations of Antarctic Sea ice using historical commercial humpback whale catch data

The story of Southern Hemisphere humpback whales through time presents multiple narratives. This study integrated two of those narratives to better understand our climate over time - the ecological behaviour of this species as well as their exploitation in the last century. The changing of our climate is largely better understood from the introduction of satellites in the late 20th century when data could be collected at higher spatial and temporal levels. Prior to this, data were scarce, especially for remote areas such as the Southern Ocean. The trust on climate models to produce valuable projections rely on how skilled they are in reproducing the historical climate; therefore their results require assessments against as many observations as possible to further increase their reliability. The Southern Ocean being an integral component to climate regulation, it is important to try understand its oceanographic features. The seasonal sea ice cover represents one major feature of this system. This study proposes to use other sources of data for the early 20th century that will help closing the gap prior to satellite observations. Humpback whales migrate poleward during the austral summer to feed on Antarctic krill at a proximity to the ice edge. Humpback whale catch locations in the early 20th century corroborate with this foraging behaviour. Using humpback whale catch location data as a benchmark, the study aims to assess the skill of climate models in simulating sea ice edge location for the early 20th century. Sea ice edge is directly related to sea-ice extent, which is an important variable in the research of sea ice dynamics over time. This is especially true in the face of rapid climate change where accuracy of sea ice changes is very important. The study therefore also aims to assess climate model climatological seasonal cycle of sea ice extent results from climate models against literature and contemporary observations. Comparisons between each model's results are also carried out. The humpback whale catch effort, as per IWC data, mostly covered the Atlantic and the Indian sector of the Southern Ocean. For this reason, the study focused on these two sectors for the analyses. Decade 1930-1939 showed the highest catch numbers consistently throughout the months of the study. The simulated past century and recent climatological seasonal cycle sea ice extent show a wide variety of responses between the models, with the majority of them underestimating the seasonal cycle based on previous literature and contemporary observations. This indicates the need to improve the sea ice physical processes in models to better capture the specific Southern Ocean processes. The ensemble median of ice edge location from the models apparently follow the latitudinal pattern of the whale catch locations, which are assumed in this study to mark the topography of the sea ice edge. However, they simulate a sea ice edge equatorward of the edge derived from an ensemble analysis of humpback whale catch locations. The variance explained by the coefficient of determination between the models and the whale catch distribution is low, with the highest value of one month being low as well. This indicates that only a portion of the simulated edge follows the reconstructed sea ice features