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Dryad

Geographic variation and temporal trends in ice phenology in Norwegian lakes during a century

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Jan 21, 2021 version files 479.45 KB

Abstract

The physical characteristics of ice formation in water courses are ideal for studying climatic variation in space and time. We used a large set of observations for 9-116 years (1890-2019) of the timing of freeze-up and break-up, and the length of ice-free season for 99 Norwegian lakes to elucidate variation in ice phenology across space and time. The dataset of Norwegian lakes is unusual, covering considerable variation in altitude (4 – 1401 m above sea level) and climate (varying from oceanic to continental) within a large latitudinal and longitudinal gradient (58.2 – 69.9 °N; 4.9 – 30.2 °E).

The average date of ice break-up occurred later in spring with increasing altitude and latitude, but earlier in spring with increasing longitude. The average date of freeze-up and the length of the ice-free period decreased significantly with altitude and longitude. No correlation with distance from the ocean was detected. The geographical gradients are related to regional climate due to adiabatic processes (altitude), solar radian (latitude) and the degree of continentality (longitude).  There was a significant lake area effect as small lakes froze-up earlier due to less volume. There was also a significant trend that lakes were completely frozen over later in the autumn in recent years. After accounting for the effect of long-term trends in the large-scale NAO index, a significant but weak trend over time for earlier ice break-up was detected. An understanding of the relationship between ice phenology and geographical parameters is a prerequisite for predicting the potential consequences of climate change on ice phenology. Changes in ice phenology will have consequences for the behaviour and life cycle dynamics of the aquatic biota.