No abstract

Abstract. Annual indices of sea ice severity in Hudson Strait, for the period 1751 to 1870, are derived from written historical evidence contained in ships' log-books. These logs were all kept on Hudson's Bay Company ships sailing from London to the Company's trading posts. The log-books are homogeneous in nature and this property facilitates their numerical interpretation. The annual indices are subjected to face validity testing which indicates that they may plausibly be accepted as measures of sea ice severity. The results are examined in relation to the presentday behaviour of sea ice in Hudson Strait and they provide evidence that the summer severity of ice conditions is mainly determined by atmospheric circulation conditions.

Indices of summer sea ice severity in the eighteenth and nineteenth centuries have been reconstructed from sailing ships' log-books. The ice record for Hudson Strait extends from 1751 to 1889. Ice records are available for two parts of Hudson Bay and these extend from 1751 to 1870. The three records were derived from the same sources but the method of derivation applied in the bay was different to that applied in the strait. The years having the five largest ice indices in each of these records were identified. Also identified were the years in which major volcanic eruptions occurred between 1751 and 1889. The number of concurrences between the years with severe ice in Hudson Strait and the years with major eruptions was significant at the 99.5% level. In the western part of Hudson Bay this significance level was 95%. The years with severe ice in eastern Hudson Bay did not concur with major eruptions.

The log‐books of the Hudson's Bay Company supply ships are the sources from which are derived annual indices of summer sea ice severity in eastern Hudson Bay in the period 1751–1870. The indices are based on two properties of the daily ice conditions described in the log‐books: lateness of occurrence and severity of ice. The annual ice index is obtained by comparing the ice conditions in each year from 1751 to 1870 with those in 1969. This year experienced the most severe late summer ice in this region during the period of present‐day ice observations. Les livres de bord des bateaux d'approvisionnement de la Compagnie de la Bale d'Hudson constituent les sources desquelles sont derives les indices annuels de sévérité de la glace marine estivale, dans la partie est de la Baie d'Hudson, pour la période 1751–1870. Ces indices de la glace sont établis à partir de deux propriétés des conditions quotidiennes de la glace, telles qu'elles sont décrites dans les livres de bord. Ces propriétés sont la tardiveté d'apparition et la sévérité de la glace. On obtient l'indice annuel de la glace en comparant les conditions de la glace pour chaque année de la période 1751–1870 avec les conditions de la glace en 1969. Cette année se charactérise par la glace d'été tardive la plus sévére dans cette région au cour de la période contemporaine d'observations de la glace.

Descriptions of sea ice in Hudson's Bay Company ships' logbooks and tradiig post journals are used to reconstruct sea ice conditions in Hudson Bay, James Bay, and Hudson Strait in the summer of 1816. The results demonstrate that exceptionally late sea ice dispersal occurred in James Bay, southeastern Hudson Bay, and at the western extremity of Hudson Strait. A relatively intense flow of ice in the Labrador current occurred at the eastern extremity of Hudson Strait. These patterns of ice behaviour are indicative of the prevalence of northwesterly atmospheric circulation over this region in the summer of 1816.