Climate variability

The primary weather systems in the vicinity of Iceland are the Icelandic Low and the Greenland High. The relative strength of those two systems greatly influences the climate over the Northern hemisphere. The track of the low as it traverses the Atlantic is also of importance, e.g. whether it goes west or east of Iceland. This, together with the contrasting water masses occupying the Icelandic waters and their varying distributions, makes the climate in Iceland and its waters highly variable. These factors have for centuries produced natural climate variability. In recent years, it has become increasingly evident that the planet is warming due to the release of greenhouse gases to the atmosphere from human activity. To separate these two kinds of climate variability at a certain location is very difficult, especially in a region of large natural variability as in Iceland.

The most stable marine climate is off the south coast, where the relatively homogeneous, warm and saline Atlantic water dominates. Otherwise the temperature and salinity conditions in the ocean around Iceland are very variable in time, particularly over the shelf north of Iceland, where the Polar Front separates the contrasting Atlantic and Polar water masses. This is mainly due to large variations in the relative amounts of Atlantic and Polar water over the northern shelf. It has been shown that strong northerly winds can reduce and even stop the flow of Atlantic water to the north Icelandic shelf while southerly winds tend to increase it. Atlantic water is usually evident as a tongue of relatively warm and saline water, but the temperature and salinity decrease in the direction of the flow due to mixing with colder, less-saline water from the north and freshwater runoff from land.

The marine climatic conditions north of Iceland have been monitored for over 50 years at a hydrographic section across the shelf north of Iceland. After a generally warm period in the northern North Atlantic from 1920 to 1964, the period from 1965 to 1971 was characterized by very low temperatures and salinity typical of polar water. This was often accompanied by sea ice over the northern shelf. In some of those years, the sea ice covered the whole north and east coasts of Iceland. Temperature differences in the waters north of Iceland between these two periods were up to 3°C. Between 1971 and 1995 there were shifting periods of warm and cold conditions.

During 1996 temperatures north of Iceland increased again, and since then the temperature has been relatively high and accompanied by higher salinity as well, indicating an intensified flow of Atlantic water to the area. The increase in temperature and salinity has also been observed south of Iceland in the recent years. In fact this is part of a larger-scale change observed in the northern North Atlantic Ocean. South of Iceland, regular monitoring of the hydrographic conditions started in 1970 and during the past decade record high temperatures and salinities have been observed. This is not the case for the Siglunes section, where the present temperature does not exceed the temperature observed during the warm period from 1920-1964. Whether this recent warming is due to global warming caused by emission of greenhouse gases, or due to a natural change in the circulation in the North Atlantic is uncertain. A combination of both is most likely, but their relative contributions are unknown.

References and further information

References: (Malmberg & Valdimarsson 2003), (Ástþórsson et al. 2007).

For full citation and further information on the ecosystem in general see this page

Steingrímur Jónsson, The Marine Research Insitute/University of Akureyri