The Seasonal Temperature-Salinity Structure of a Glacial Lake: Jökulsárlón, South-East Iceland

Abstract

Measurement of water temperatures and salinities in proglacial lake Jökulsáilón made during the spring, summer and winter months allows the structure of the lake water, together with its seasonal variations, to be described. A distinct thermal stratification is present during the summer season when a weakly developed thermocline separates warmer surface water from deep-lying cold, isothermal water. Multiple temperature inversions occur within the water column, implying that the thermal structure of the lake in summer is a dynamic one. In the winter months water at all depths and in all parts of the lake is isothermal at 0° C.Intermittent reversals of flow in the channel connecting the lake with the sea occur at all seasons and this allows saline water to enter the lake. The vertical and spatial distribution of salinity in Jökulsárlón varies greatly at different times of the year. For up to nine months of the autumn, winter and spring seasons the salinity pattern in the lake—a rapid increase at the surface followed by a smaller steady increase to a maximum of 10.5 ‰ to 12.5 ‰ at the base of the water column—appears to remain unchanged. During the summer months glacial melt-waters flush this salt water from the lake but leave a bottom-lying saline body of water (of maximum salinity 5 ‰) in one of the deepest areas of the lake basin. The implications that these temperature and salinity variations have for sedimentation in the lake are mentioned. It is considered that the presence of salt water in Jökulsárlón inhibits the formation of diatactic varved sediments, samples of which are known from neighbouring freshwater lakes of the Breidamerkurjökull.