The water that flows into Eyjafjörður normally originates in the Irminger Current which is a branch of the Gulf Stream or the North Atlantic Current as the Gulf Stream is called after it leaves the coast of USA east of Cape Cod. The Irminger Current transports Atlantic water, which is relatively warm and saline, along the west coast of Iceland.

Off Breiðafjörður it splits into two branches with the larger one crossing the Irminger Sea towards Greenland where it subsequently flows southwards over the Greenland continental slope. A smaller branch continues northwards along the West Fjords and enters the north Icelandic shelf and then flows eastwards along the north coast. Along its path the Atlantic water mixes with freshwater from land and the salinity decreases, especially close to land. The water also cools on its way northwards. By the time the Atlantic water reaches Eyjafjörður it has lost most of its original character by mixing and cooling.

Sometimes cold and low salinity polar water that originates from the Arctic Ocean is brought in large quantities to the north Icelandic shelf and then flows eastwards over the shelf. This water brings with it sea ice and it has for a long time been feared in Iceland because it brings with it deteriorating climate both on land and at sea.

Sea ice was hardly observed after 1920 until suddenly in spring 1965 all fjords and bays on the north coast, including Eyjafjörður, were filled with sea ice. Then it was a regular visitor to Iceland until 1971 but after that sea ice has been much less frequently observed

Steingrímur Jónsson