Waves and tides

Both waves and tides cause mixing in the ocean that can be of importance to many marine species. They affect the coastal geomorphology as they shape the coastal landscape. They have also to be taken into account when considering constructions along the coast and offshore.

If one travels from Iceland’s south coast along the 20°W longitude southwards, the next continent one encounters is Antarctica. Travelling in any other direction from the coast of Iceland also takes you over vast oceanic areas before reaching land. Thus the wind has ample time and space to create large waves before they reach the Icelandic coast. It is therefore not surprising that the wave climate around Iceland is harsh, especially considering the fact that the Icelandic low, one of the most powerful weather systems in the world, regularly traverses the area. Only around Antarctica is there a stronger wave climate than in the area south of Iceland. The coast of Iceland and, in particular, the south coast is in most places rather exposed to the open ocean and therefore experiences great impact from large ocean waves.

The tides in Iceland are mainly of semidiurnal type or M₂, which means that there are 12 hours and 25 minutes between consecutive floods. The tidal wave arrives from the south and then rotates clockwise around Iceland in 12 hours and 25 minutes. The mean speed of the wave is around 150 km/hour. There is an amphidromic point in the Denmark Strait and another one close to the Faroe Islands. Amphidromic point is where the tidal range is almost zero. The tidal elevations in Iceland are greatest on the west coast, especially in Breiðafjörður where the difference between ebb and flood for mean spring tides can exceed 4 meters. Along the north and east coasts, this difference is considerably smaller, typically 1-2 meters.

Since the tides involve movement of water, tidal currents are associated with them. These currents can become very strong where there are constrictions through which the water must go. This occurs in Breiðafjörður at Hvammsröst, where there is a narrow entrance to the fjord Hvammsfjörður in the inner part of Breiðafjörður, and the current reaches several m/s. Also off some peninsulas, in particular Reykjanes, Látrabjarg and Langanes, strong tidal currents occur when the tidal wave has to pass the peninsulas. However, no direct measurements of those strong tidal currents have been made. Apart from those special regions, the strongest tidal currents are observed along the east coast where the tidal elevations are very small. Direct measurements have shown tidal currents with amplitude exceeding 50 cm/s. In other areas typical tidal currents have an amplitude of about 10 cm/s. The tidal currents are even smaller in many fjords along the north and east coast with an amplitude of only about 5 cm/s.

The Icelandic Maritime Administration publishes regular forecasts on the web of waves for the area around Iceland They also provide forecasts of tides and storm surges for the area.

References and further reading

The Icelandic Maritime Administration wave-forecast

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

Steingrímur Jónsson, The Marine Research Insitute/University of Akureyri