A Northern Meddy at the Mid-Atlantic Ridge

Within the scope of the international project NA-VICE, an oceanographic campaign was conducted from the Azores to Iceland in the summer of 2012. During this campaign, a Mediterranean Water Eddy (meddy) was identified at 41.3ºN, 27.1ºW. Meddies are deep subsurface anticyclones containing anomalously warm, saline modified Mediterranean Water. Generated at the topographically trapped Mediterranean Undercurrent, they can transport salt and heat great distances from the eastern boundary, accounting for at least half of the Mediterranean Water salt flux into the North Atlantic. Despite their significant role in forming the Atlantic intermediate water masses, their life cycle remains poorly understood. In this study, a meddy was identified using vertical CTD casts and ADCP data. Its core was located between 900 and 1100 m and was characterized by a salinity anomaly of 0.26, a temperature anomaly of 2.4 °C, and a negative anomaly in the buoyancy frequency. Tracing the meddy via its sea-surface manifestation and an Argo float suggests that it originated on the Irish continental slope and moved southwest toward the Mid-Atlantic Ridge. The existence of meddy generation sites well north of the Iberian Peninsula, not listed in recent studies, implies that meddies’ contribution to the heat and salt budget of the North Atlantic mid-depths might be underestimated. The detailed ADCP observations during the cruise suggest that, at that time, the meddy was interacting with a strong surface cyclone, which trapped a portion of the Mediterranean Water from the meddy, thus contributing to its decay. Future studies should investigate the additional contribution of meddies generated north of the Iberian Peninsula to the thermohaline balance of the interior North Atlantic.