Jökulsárlón at Breiðamerkursandur, Vatnajökull, Iceland: 20th century changes and future outlook

We describe ice fluxes and calving rates of the terminus of Breiðamerkurjökull, SE-Vatnajökull, since the formation of the proglacial lake Jökulsárlón in the 1930s.Breiðamerkurjökull retreated 4 km during the 20th century and the lake is now 15 km in area.Field observations in 1997 to 1999 revealed ice flow toward the lake with an average velocity of 258 m yr .The calving rate was estimated at 582 m yr and the calving ice flux at m yr .The thermal energy required to melt the ice calving into Jökulsárlón is at present about 2500 MW, of which approximately half to two-thirds, is supplied by warm seawater flowing into the lake.An empirical relationship is derived for the calving rate as a function of the water depth at the calving front.Past ice fluxes at the terminus of Breiðamerkurjökull are simulated using theoretical models and possible future changes predicted for given mass balance scenarios.Both the ice fluxes toward the lake and the calving rates into the lake have increased rapidly during the last two decades.Model calculations suggest similar retreat rate of the calving front position for the next 70 years which would imply an average lake growth rate of 0.5 km yr .At that rate Breiðamerkurjökull would retreat from the lake depression after 200 years and almost vanish in 400 years.