Trends in the Dates of Ice Freeze-up and Breakup over Hudson Bay, Canada

Abstract

ABSTRACT. Hudson Bay experiences a complete cryogenic cycle each year. Sea ice begins to form in late October, and the Bay is usually ice-free in early August. This seasonally varying ice cover plays an important role in the regional climate. To identify secular trends in the cryogenic cycle, we examined variability in the timing of sea-ice formation and retreat during the period 1971-2003. The dates of ice freeze-up and breakup at 36 locations across Hudson Bay were catalogued for each year from weekly ice charts provided by the Canadian Ice Service. We used the nonparametric Mann-Kendall test to determine the statistical significance of the trends and the Theil-Sen approach to estimate their magnitude. Our results indicate statistically significant trends toward earlier breakup in James Bay, along the southern shore of Hudson Bay, and in the western half of Hudson Bay, and toward later freeze-up in the northern and northeastern regions of Hudson Bay. These trends in the annual ice cycle of Hudson Bay coincide with both the regional temperature record and the projections from general circulation models. If this trend toward a longer ice-free season continues, Hudson Bay will soon face important environmental challenges. Le test non paramétrique Mann Kendall a été utilisé pour déterminer la signification statistique des tendances alors que la méthode de Theil Sen nous a fourni un estimé de l'ampleur de ces mêmes tendances. Notre analyse statistique nous indique qu'il existe des tendances significatives vers une date de déglacement plus avancée dans la Baie James, le long de la côte sud de la Baie d'Hudson, et dans la partie ouest de la Baie d'Hudson. De plus, des tendances significatives vers un gel plus tardif ont été observées dans les régions du nord et du nord-est de la Baie d'Hudson. Ces tendances dans le cycle annuel de glace de la Baie d'Hudson coïncident avec les tendances des températures de la région de même qu'avec les projections des modèles de circulation générale. Si cette tendance vers une durée plus courte du couvert de glace continue, la région de la Baie d'Hudson relèvera des défis environnementaux importants dans un proche avenir.

Observations: Cryosphere

“…The dynamic, rather than climatic, aspect of seaice change is well exemplified in a recent satellite study by Scott and Marshall (2010), who aimed to resolve a dilemma: Whereas there has been a trend toward earlier summer breakup of sea ice in western Hudson Bay, Canada, which some authors (Stirling et al, 1999;Gagnon and Gough, 2005) have attributed to long-term warming in the region, Dyck et al (2007) report no regional warming trend has elapsed sufficient to have caused this change.…”

Climate Change in the Hudson Bay Complex: Opportunities and Vulnerabilities for the Port of Churchill's Marine Operations

“…For example, the relatively early breakup of sea ice in eastern Hudson Bay has been attributed to the large volume of fresh water flowing northward along the coast after the spring runoff in James Bay (Gagnon and Gough, 2005). The input of fresh river water may be locally important in initiating break-up in other areas of the Bay as well, as spring freshets tend to arrive when the Bay is still ice covered; this arrival of liquid water accelerates the melt and break-up processes (Ingram et al, 1996).…”

“…The timing, thickness, and extent of sea ice are extremely important to both the wild and human populations of the Hudson Bay Complex . The entire Complex typically undergoes a complete freeze and thaw cycle every year and second year ice is found only on rare occasions (Gagnon and Gough, 2005).…”

“…Hudson Bay and Hudson Strait are usually ice free by late-July or early August and Foxe Basin follows suite by mid-September . It should be mentioned that the freeze-up and breakup dates of all three areas of the Hudson Bay Complex exhibit high interannual variability, and sea ice timing in some regions can vary by as much as a month from year to year depending on local factors (Gagnon and Gough, 2005). Freeze-up: late October to early December.…”

“…The south-western regions of Hudson Bay are typically the last regions to be ice free due to wind and circulation patterns which drive drifting ice into the area (Gagnon and Gough, 2005). These final areas are usually ice free by early August .…”