Temperature and salinity

Iceland is surrounded by two primary water masses with very different origins and properties. Originating far south, the warm and saline Atlantic water is brought by the North Atlantic drift towards the southern shores of the country. This water mass is several hundred metres thick and very homogeneous. When it approaches Iceland it is about 10°C and the salinity is about 35.2. The water then flows westward as the Irminger Current and eventually north along the west coast. Along this route it cools down and the salinity decreases. Most of this water turns west towards Greenland and subsequently flows southwestward along the slope off Greenland. A smaller branch continues northwards onto the north Icelandic shelf area as the North Icelandic Irminger Current. As the water enters the North Icelandic shelf, it has cooled down to 4-5°C and the salinity has dropped to about 35.0. The cooling and dilution continues as the water moves eastwards along the north coast and when at the northeast corner of Iceland, the Atlantic water characteristics are lost.

The other primary water mass is the Polar water, which originates in the Arctic Ocean. It is relatively fresh ( S ≤ 34.5 ) and very cold ( T ≤ 0 °C). It flows as the East Greenland Current out of the Arctic Ocean through the Fram Strait between Spitsbergen and Greenland. Below the Polar water, at 150-400 m depth, the East Greenland Current transports remnants of Atlantic water, with salinities as high as 35.0 and temperatures above 0°C. This water mass originates from the Norwegian Atlantic Current that crosses the Fram Strait and sinks under the Polar water. The East Greenland Current also brings sea ice from the Arctic Ocean along the whole coast of East Greenland and even beyond Cape Farewell. Some of the ice is occasionally transported into north Icelandic waters. In extreme years it can cover the north and east coasts of Iceland and has even been observed to almost surround the country.

The mixing and cooling of different parts of Atlantic and Polar waters form almost all the other water masses in the area, and these mixtures are usually called Arctic waters. An exception is the low salinity coastal water mass in spring and summer caused by freshwater run-off that circulates clockwise around Iceland with the general circulation. In the surface layers over the Iceland Plateau, there is a mixture of Polar water from the East Greenland Current and Atlantic water that enters the Iceland Sea south of Jan Mayen and to a lesser extent from the North Icelandic Irminger Current. This water has temperatures generally below 0°C and salinities less than 34.9. It leaves the Iceland Sea to the east with the East Icelandic Current along the northern slope of the Iceland-Faroe Ridge and eventually dives under the Atlantic water in the Norwegian Sea.

Several deep water masses are formed in the seas north of the Iceland-Scotland Ridge. In the Arctic Ocean, deep water is formed over the shelves by freezing. This causes an increase in the salinity of the water remaining under the ice. This Arctic deep water flows through the Fram Strait with the East Greenland Current towards the Denmark Strait. It partly fills up the basin in the Greenland Sea and also the Iceland Sea. However, most of the deep water in the Iceland Sea is deep water from the Norwegian Sea, caused by cooling and subsequent sinking of North Atlantic drift waters. All these deep water masses are rather cold (T < -0.5°C) and the salinity is very stable at around 34.90.

References and further information

References: (Malmberg & Valdimarsson 2003), (Buch et al. 1996)

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

Steingrímur Jónsson, The Marine Research Insitute/University of Akureyri