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From Arctic to Atlantic oceans: currents along Greenland's east coasts

Ocean currents are major actors in climate regulation, yet some of them are still poorly known. This is the case of those flowing along Greenland's east coasts, which have long been identified but whose water transport has rarely been measured. This set of currents named "East Greenland Current - Irminger Current" (EGIC) is an important component of the subpolar oceanic circulation. It contributes to the transport of waters mixed and made denser in the Irminger Sea towards the area of deep water formation in the Labrador Sea; in this region, between south Greenland and Labrador, these waters complete their transformation, sink and are incorporated in the Atlantic meridian overturning circulation. In the context of a warming of the Arctic Ocean, a strengthening of EGIC could have significant climatic consequences.

Carte_Ovide

North Atlantic section studied during Ovide cruises and EGIC study area (red frame)

Within Ovide project (Observatory of interannual to decennal North Atlantic variability), a set of current meters were moored along a ~100 km-long line perpendicular to the direction of these currents, from the southeast tip of Greenland to a depth of about 2000 m. These instruments recorded data from June 2004 to June 2006. Two types of current meters were used on these fixed moorings: some measured current direction and speed with a vane and a propeller, whereas others used Doppler effect to make an acoustic measurement of the movement of particles carried by the current. In addition, this latter kind of measurement was made by the research vessels during the cruises where fixed current meters were moored (2004) and hauled (2006). All the current speeds were measured with a precision around 1 cm/s.

 

Couranto1

Couranto2
The two types of current meters used during one of the cruises
(photos Ifremer/Ovide)

The data recorded by the ships in 2004 and 2006 show the main currents flowing south-east alongside the underwater topography of Greenland coast, with speed reaching and sometimes exceeding 50 cm/s. Close to the shore, the East Greenland Coastal Current flows in surface waters above the continental shelf. Farther offshore, the EGIC extends from the surface to more than 1000 m.

Daniault_fig5
Current speed (cm/s) along a section perpendicular to the coast. East Greenland Coastal Current (above continental shelf) and EGIC (offshore) are clearly visible in red

 

The data recorded during two years by the moored current meters confirm that these current are far from being steady flows: contrary to their direction which is almost constant, their speed is highly variable, and they can even reverse occasionally in winter. This variability, which decreases with depth, includes a weak seasonal cycle (a few cm/s) and mainly a strong high-frequency variability (less than one month) of several tens of cm/s at the surface.

The volumes of water transported by the currents were computed from the speed measured by each current meter and the corresponding area crossed by the water. Oceanic currents are measured in Sverdrup (Sv), unit equal to 1 million m3 per second (to give orders of magnitude, the average transport of Amazon River is 0.2 Sv, and that of Gulf Stream is 30 Sv off Florida and 150 Sv off Nova Scotia). On the average, 17.3 million m3 cross each second the section perpendicular to the coast off Greenland. Of course this volume is highly variable, and instantaneous values from 5 to 23 Sv were observed. This variability is mainly driven by the wind over Irminger Sea, but characteristics of upstream circulation (eddies, current inflexion) could also contribute to explain it.

 

The paper

Daniault M., Lherminier P., Mercier H., 2011. Circulation and Transport at the Southeast Tip of Greenland. Journal of physical oceanography, 41: 437-457.

 

The authors

The three authors of the paper are from the Laboratoire de physique des océans (IUEM), but Ovide project and cruises are a partnership between French (LPO ; Laboratoire de chimie marine, Roscoff; Laboratoire d'océanographie et du climat, Paris) and Spanish (IIM, Vigo) scientists.

 

The journal

Published by the American Meteorological Society, Journal of physical oceanography is an monthly international journal devoted to observational, theoretical, and modeling studies of the physics of oceans and to processes operating at its boundaries (interactions between ocean and atmosphere, physics and biology, physics and chemistry).

 

Contacts

Authors : browse IUEM staff directory
Communication and outreach service: communication.iuem@univ-brest.fr


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