Oceanography

Oceanography

The continental shelf around Iceland is generally fairly wide, except off the south coast, sometimes stretching as far as 150 kilometres from the coast. Beyond the shelf, the depth to seabed is about 1000 metres compared to an average depth of 200 to 400 metres on the shelf. The Icelandic EEZ includes almost the entire continental shelf around Iceland.

Three major current systems

Three major current systems influence Icelandic waters. The warm and saline Irminger current, an offshoot from the Gulf Stream, the cold and less saline East-Greenland current flowing directly from the Arctic, and the intermediate East Icelandic current from the Northeast, a merger of cold Arctic waters and warmer Atlantic waters northeast of Iceland. As the Irminger current makes its way along the west and north coasts of Iceland, it mixes with the colder currents causing increase in vertical mixing which leads to enhanced primary production.

The Marine Research Institute (MRI) has by law as one of its tasks to improve knowledge on the physical and chemical oceanography of Icelandic waters, particularly in relation to  biological resources and their productivity. For this purposes, the oceanography group at MRI runs various projects monitoring the environment and climate parameters.

Monitoring since 1950

In order to monitor and climatic variations, annual observations of temperature and salinity have been been undertaken since 1950 at a number of fixed locations on the Icelandic shelf. Initially only done once a year in the springtime, the MRI has since 1970 monitored these locations on a quarterly basis. The findings provide baseline information for studies on marine ecology. Simultaneously, nutrients are monitored as well as primary production of phytoplankton and the abundance and species of zooplankton to name just a few tasks.

In the quarterly cruises there has been regular monitoring of carbon dioxide in the sea in addition to several other paramenters,  for example trace elements, radioactivity and sediment flux.

Topography

Located in the northern North Atlantic Ocean, Iceland is just south of the Arctic Circle. The island is the largest part of the Mid Atlantic Ridge that rises above sea level. Apart from the sandy southern coast, Iceland‘s coastline is interspersed with fjords and bays in an array of shapes and sizes that provide good facilities for harbours.

A typical cross section of an Icelandic fjord has steep sides and a flat bottom filled with sediments. Approaching the open shelf, the fjords gradually deepen to 100-200 metres. Only a few have shallow thresholds. This makes them different from many fjords in other high latitude regions.

Ranging from 20 kilometres at its narrowest up to 150 kilometres where it is widest, the continental shelf is indented by deep channels, often an extension of the fjords. Depth rises steeply at the shelf break before sloping more gently towards the abyss.

At a junction of ridges

Iceland lies at the junction between two submarine ridges, the Mid Atlantic Ridge and the Greenland-Scotland Ridge. The exchange of water across the Greenland-Iceland Ridge through the Denmark Strait and over the Iceland-Faroe Ridge is of particular importance as both present a division of waters below their threshold depth of 620 and 550 metres. Only a narrow channel with depths exceeding about 300 m separates the Icelandic shelf and the broad shelf off Greenland. In contrast the Iceland-Faroe Ridge has a more even depth of 400-550 m over its whole length.

The Mid-Atlantic Ridge to the southwest of Iceland is called the Reykjanes Ridge, it‘s extension gradually increasing in depth. To the north of Iceland the ridge is named the Kolbeinsey Ridge, stretching to the Jan Mayen fracture zone between Jan Mayen and Greenland. South of Jan Mayen, the Iceland-Jan Mayen Ridge extends to the Iceland-Faroe Ridge and separates the Iceland Sea from the Norwegian Sea.

A natural boundary

The northern boundary of the Iceland Sea is the Jan Mayen Fracture Zone, separating it from the Greenland Sea. To the south, the Greenland-Iceland Ridge provides a natural boundary. The Iceland Sea is split in half by the Kolbeinsey Ridge. It‘s eastern half, the Iceland Plateau, reaches to a depth of 2200 metres. West of the ridge, a channel connects to the Denmark Strait, bordered in the west by the East Greenland shelf. While the Iceland Basin lies south of Iceland and east of the Reykjanes Ridge, the Irminger Sea is west of the Reykjanes Ridge between Iceland and Greenland.


Ocean currents and climate

Surface water circulation around Iceland is fairly well studied. Once the Gulf Stream approaches, bringing warm and saline water from the south, it splits into two branches. One flows east, towards The Faroe Islands while the other, The Irminger Current, flows north along the west coast of Iceland.

Most of this water branches off into the Irminger Sea and then follows the East Greenland slope southwards. A relatively small branch continues farther northeast through the Denmark Strait and along the shelf north of Iceland.  There is a further coastal water mass, visible as a low salinity band close to the coast during spring and summer that flows clockwise around Iceland along with the Irminger current.

Impact of currents

The swifter East Greenland Current flows from the North along the shelf and slope off East Greenland, bringing cold low salinity water close to Iceland mainly through the Denmark Strait. However, a small but highly variable percentage finds its way into the Iceland Sea, occasionally covering the shelf off the north coast.  The East Icelandic Current brings a flow of cold water over the slope north east of Iceland.  

The fastest currents around Iceland travel just above the seabed, over the Iceland-Faroe Ridge and particularly in the Denmark Strait. These currents are the results of deep water formation occurring north of the Greenland-Scotland Ridge, filling up the deeper levels of the ocean north of the ridge until it spills over the Greenland-Scotland Ridge and into the North Atlantic.

The most stable marine climate is off the south coast, where the relatively homogeneous, warm and saline Atlantic water dominates. Over the shelf north of Iceland, where the Atlantic and Polar water masses mix, ocean conditions can vary greatly depending on strength of wind.

Climate change concerns

Iceland‘s weather system is primarily defined by the Icelandic low-pressure area and the Greenland high-pressure area, the strength of which greatly influences the climate in the Northern hemisphere. The combined effort of lows and the contrasting water masses and their varying distribution around Iceland has long had a defining effect on ocean conditions.

The conditions in Icelandic waters during the 20th century can be roughly divided into four periods. Generally cold until 1925, followed by a warmer period lasting until 1964, a brief cold period affected Icelandic waters until 1971. Conditions then fluctuated between short warm and cold periods until 1995. Conditions have since been generally been warm.

There have been concerns that the pattern of the main currents in the North Atlantic might be altered due to climate change, and in particular large amounts of fresh water coming from the melting ice in the north. At this stage it is, however, extremely difficult to make any predictions due to the complex interactions between the land, sea and atmosphere that are far from fully charted.