Observations of Irminger Sea Anticyclonic Eddies

Xue Fan (1) , Uwe Send (1) , Pierre Testor (2) , Johannes Karstensen (3) , Pascale Lherminier (4)

1 SIO - UC San Diego - Scripps Institution of Oceanography
2 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
3 IFM-GEOMAR - Leibniz-Institut für Meereswissenschaften
4 LPO - Laboratoire de physique des océans

Mesoscale anticyclonic eddies in the Irminger Sea are observed using a mooring and a glider. Between 2002 and 2009, the mooring observed 53 anticyclones. Using a kinematic model, objective estimates of eddy length scales and velocity structure are made for 16 eddies. Anticyclones had a mean core diameter of 12 km, and their mean peak observed azimuthal speed was 0.1 m s⁻¹. They had core salinities and potential temperatures of 34.91-34.98 and 4.48°-5.34°C, respectively, making them warm and salty features. These properties represent a typical salinity anomaly of 0.03 and a temperature anomaly of 0.28°C from noneddy values. All eddies had small (≪1) Rossby numbers. In 2006, the glider observed two anticyclones having diameters of about 20 km and peak azimuthal speeds of about 0.3 m s⁻¹. Similar salinity anomalies were detected throughout the Irminger Sea by floats profiling in anticyclones. Two formation regions for the eddies are identified: one to the west of the Reykjanes Ridge and the other off the East Greenland Irminger Current near Cape Farewell close to the mooring. Observations indicate that eddies formed in the former region are larger than eddies observed at the mooring. A clear increase in eddy salinity is observed between 2002 and 2009. The observed breakup of these eddies in winter implies that they are a source of salt for the central gyre. The anticyclones are similar to those found in both the Labrador Sea and Norwegian Sea, making them a ubiquitous feature of the subpolar North Atlantic basins.

Mots clés: Mesoscale processes; Eddies; North Atlantic Ocean

Domaines: Océanographie

Xue Fan, Uwe Send, Pierre Testor, Johannes Karstensen, Pascale Lherminier. Observations of Irminger Sea Anticyclonic Eddies. Journal of Physical Oceanography, 2013, 43 (4), pp.805-823. ⟨10.1175/JPO-D-11-0155.1⟩. ⟨hal-00836621⟩