Estimating summer sea ice extent in the Weddell Sea during the early nineteenth century

Abstract. Over the past three decades, discordant trends in sea ice extent have been observed between the Arctic and Antarctic regions. Arctic sea ice extent has been characterised by a rapid decline, whereas Antarctic sea ice extent, while highly variable inter-annually, has tended to increase. Climate models have so far failed to capture these trends. Coupled with the limited pre-1970 sea ice dataset, this poses a significant challenge to quantifying the mechanisms responsible for driving such trends. However, historical records from early Antarctic expeditions contain a wealth of information regarding the nature and concentration of sea ice. Such records have been under-utilised, and their analysis may enhance our understanding of recent Antarctic sea ice variability. For the purpose of this study, 9 records from 8 Antarctic expeditions have been examined. Summer sea ice positions recorded during 1820–1843 have been compared to satellite observations from 1987–2017, as well as historical data for the period 1897–1917. Through analysis of these three time series, estimations for summer sea ice extent in the Weddell Sea, during the early nineteenth century have been produced. The key findings of this study indicate a nineteenth century average core summer northernmost sea ice latitude in much of the Weddell Sea that was further north than during the modern era, with nineteenth century February having significantly more sea ice by all measures. However, late summer sea ice was most extensive in the early years of the twentieth century.