The role of the ocean circulation in melting the glaciers in Iceland

Iceland enjoys a much warmer climate than the average for its latitude. A major reason for this is the warm ocean currents in the Atlantic south of Iceland. There is a large heat flux from the ocean to the atmosphere and the air temperature therefore depends to a high degree on the ocean temperature. During the last roughly two decades, glaciers in Iceland have generally been retreating as well as having a negative mass balance due to a warmer climate, whereas during three decades prior to that, most of the glaciers in Iceland were advancing. The air temperature in Iceland south of the largest Icelandic glacier, Vatnajökull, showed a rise in temperature of about 1°C from 1995 to the early 2000’s and since then it has mostly remained at this high level. Often this warmer climate is attributed entirely to global warming. However, the temperature in the warm and saline Atlantic water south of Iceland also increased by about 1°C during the same period. This rise in ocean temperature was accompanied by an increase in salinity which indicates that the temperature rise was mostly due to a change in the ocean circulation, resulting in advection of warmer and saltier water to the area. In the period from 1995 to the early 2000’s the ocean heat flux with the Atlantic water across the Greenland-Scotland ridge increased by 21 TW, partly through Denmark Strait towards the continental shelf north of Iceland. The increased heat flux was attributed to a rising temperature as well as increased flow of Atlantic water. Only about 0.5% of this heat flux increase is needed to explain the recent melting of Icelandic glaciers. With a relatively sudden 1°C rise in temperature the glaciers will take decades to reach equilibrium with this new temperature and if the temperature does not decrease, the glaciers will continue to lose mass. There are records of advancing and retreating Icelandic glaciers from 1930 and they show a good correspondence with the Atlantic Multidecadal Oscillation (AMO), that reflects temperature variations in the North Atlantic Ocean.