Large-Scale Changes in Atmospheric Circulation Interpreted from Patterns of Tree Growth at Churchill, Manitoba, Canada

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Abstract
Growth layer analysis involving 11 treeline white spruce (Picea glauca) and two tamarack (Larix laricina) from Churchill, Manitoba, Canada, produced a data set with some 500,000 tree rings. A summary of these data is made using knowledge of tree growth and weather stresses. The growth trends conform well to Northern Hemisphere and Arctic temperature data sets and poorly to local temperatures. The summer position of the Arctic Front is close to the treeline and some periods of tree growth are dominated by arctic conditions while others are dominated by more temperate conditions. The period 1760 to 1820 shows intermittent dominance of temperate conditions while the period 1921 to 1970 shows a complete dominance of temperate conditions. All other years from 1715 to 1982 show a dominance of arctic conditions. Under the cool Arctic air mass the trends longer than 8 yr are suppressed and poorly defined relative to the trends in hemispheric temperature data. The presence of the Arctic Front to the north of Churchill also influences the region as dominant northerly winds travel over the Hudson Bay ice pack before reaching the coast. During warmer periods the trends are exaggerated and more variable as other air masses have a varying influence.