AbstractThe Alkor-Deep (140 m), which forms part of a depression system in the northern Kattegat channel east of the island of Læsø (Denmark), is the location of a self sustaining population of Northern krill, Meganyctiphanes norvegica (Euphausiacea). This population is exposed to one of the most pronounced thermal gradients within the distributional range of this pelagic crustacean. During summer, the tem-perature of the water column ranges between 4 to 6 °C in the deep to 16 °C near the surface which results in the krill being exposed to temperature differences of 8 to 10 °C during diel vertical migration. Oxygen consumption rates were used to investigate the physiological adaptation of the animal to such gradients in temperature. The rates were found to increase exponentially from 31 µmolO2·h-1·gdw-1 at 4 °C to 72 µmolO2·h-1·gdw-1 at 16 °C, giving a Q10-value of 2.0, and indicating that physiological adaptation to varying thermal conditions does not take place. Behavioural adaptations are discussed which may help the krill to cope with large temperature gradients in their environment.