Sea ice incidents in Icelandic waters
and their monitoring
by Thor Edward Jakobsson
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Monitoring procedures
Sea ice monitoring of Icelandic waters as well as archiving of sea ice observation data is looked after by the Icelandic Meteorological Office. Icelandic waters are defined as the economic zone around Iceland, extending outwards to a 200-nautical miles distance from the coast or to the midline between Iceland and Greenland in the Denmark Strait.
Sea ice movement
Annual extension of sea ice in the vicinity of Iceland fluctuates between open sea across the Denmark Strait in late summer to sea ice in the Strait in late winter covering the ocean at the coast of East Greenland halfway towards Iceland. Much of the sea ice is carried by the East Greenland Current from the Arctic Ocean and the Northern Greenland Sea but considerable amounts form during winter along the coasts of Greenland further south. Besides variable amounts being brought south by the East Greenland Current, year-to-year fluctuations in surface ocean conditions in the Denmark Strait and the Iceland Sea give rise to different sea ice extent in Icelandic waters. However, the final cause at present resulting in sea ice reaching as far east as sailing routes around northwest and north Iceland, and even to the coasts, is the effect of prevailing winds, that is, the atmospheric pressure configuration over the North Atlantic. In earlier centuries of colder climate, with more extensive sea ice in the Greenland Sea, Icelandic coasts were visited by sea ice more frequently.
Sea ice in the Denmark Strait (Greenland Sound)
The charts shown below are based on sea ice reconnaissance flights of the Icelandic Coast Guard and supplemented by ship reports and other available information.
Figure 1 displays a rather normal extent of sea ice in the Denmark Strait in June, soon after maximum extent in late May. The chart resulted from an expedition in June 1982 on board the Soviet icebreaker Otto Schmidt with Icelandic participation. Meteorological and oceanographic observations were made in the marginal sea ice zone between Iceland and Greenland. The broken line in Figure 1 displays the general position of the sea ice edge during the expedition. The encircled points show the locations of oceanographic stations. During middle of June - the month of the cruise - the sea ice is normally on retreat but still extensive.
Figure 2 shows in detail the characteristics of part of the sea ice edge investigated during the cruise, described by the international sea ice symbols, at that time newly adopted. The sea ice amount was still quite large after the gradual accumulation through the winter months. The sea ice in the southern part of the area investigated was in general characterised by thick ice. However, the overall panorama during the cruise was surprisingly variable in terms of concentration, stage of development, floe size and other ice features.
Figure 3 indicates position changes of the ice edge in the Denmark Strait in June, 1982. The eastward movement of the ice edge was associated with moderate winds from south, southwest and west.
Examples of sea ice incidents
Sea ice off the Icelandic coasts has been recorded for centuries, first by remarks in annals and diaries kept by farmers and officials, and in a more regular manner during the last couple of centuries. In an effort to find a measure of variability from one year to another, an index was developed indicating the severity of sea ice incident during a particular year along the coasts of Iceland. The index refers both to the extent of the Icelandic coastline being visited by sea ice and number of weeks with recorded sea ice during the year.
Figure 4 shows the sea ice index during most of 20th century. During the first two decades heavy sea ice was quite common along the coasts of Iceland, but in the 1920s a drastic change occurred. Sea ice along the coasts of Iceland became an uncommon characteristic and almost a forgotten phenomena around the middle of the century. An abrupt change occurred in the mid-1960s.
Figure 5 shows the distribution of sea ice along the northern coast of Iceland in February 1965. Heavy sea ice distribution occurred almost each year following, but since 1980 widespread and long-lasting sea ice off Iceland took place at rather irregular intervals.
Figure 6 displays a mid-summer sea ice distribution in 1984, showing the effect of prevailing southwesterly and westerly winds due to a dominating blocking high-pressure area over the North Atlantic.
Finally, in Figure 7 a more recent mid-winter incident in March 1988 is shown, demonstrating a combined effect of above-average sea ice extent in the Greenland Sea in the weeks before and atmospheric pressure configuration favouring westerly winds.
The sea ice index graph during this century is an indication of interesting climate changes on decadal time scales. However, changes of sea ice distribution in Icelandic waters on smaller time scales, down to a few days, and even from one hour to another, are important as sea ice affects human activities on fishery grounds, sailing routes and in the most serious scenarios can threaten access to harbours in northern Iceland. Due to its irregular, almost erratic, behaviour, sea ice around Iceland is an important natural feature that has to be watched and studied.
Scientific projects and integrated monitoring systems
In addition to conventional sea ice service based on flow of data from ships and aircraft and archiving of obtained information, the Icelandic Meteorological Office has participated in European and Nordic research projects in the North Atlantic where international co-operation results in increased knowledge of the physical processes involved in variable sea ice amount on many scales. The Greenland Sea Project (GSP) and the European Sub-polar Ocean Programmes (ESOP-1 and ESOP-2) have contributed to improved understanding of the northern seas and a series of Nordic research projects for the sub-Arctic have concentrated on analysis of meteorological and oceanographic observation time series around the North Atlantic. Useful experience in the fields of remote sensing, sea ice modelling and so on has been gained.
More on the practical operational side, a three-year European project in the field of information society technology was completed recently, called 'Integrated weather, sea ice and ocean service system' (IWICOS). Six institutions and a private company in the Nordic countries worked together on the design of a co-operating platform of marine services in the North Atlantic and along the Northern Sea Route in the Arctic Ocean. Closer co-operation between different organisations will improve service and safety at sea.
Conclusion
Despite indications of decreasing sea ice amount in the Arctic, the East Greenland Current - the main current leaving the Arctic - will continue to bring sea ice long distances south along the coasts of Greenland. Conditions for local sea ice formation en route will also persist. Helped by atmospheric variability, sea ice in Icelandic waters will still in the years to come be of concern to seafarers, be they on board small sailing boats, fishing boats, big tank ships or cruise liners.
© Thor Edward Jakobsson 2003. Dr Jakobsson is Project Manager, Sea ice Research Unit at the Icelandic Meteorological Office in Reykjavik, Iceland.
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