The physical oceanographic conditions along the Mid-Atlantic Ridge north of the Azores in June–July 2004

Abstract

Abstract During the MAR-ECO expedition in June and July 2004, 39 deep CTD stations were occupied with uneven spacing along the Mid-Atlantic Ridge (MAR) between 41°N and 61°N. The CTD stations coincided with the biological sampling stations and thus gave a detailed vertical description of the water properties at these locations. Many different water masses were identified. However, using the predominant water mass in the upper 500 m, four different hydrographic regions were identified. Stations in the vicinity of the Reykjanes Ridge north of 57°N were dominated by Modified North Atlantic Water (MNAW). Stations south of 56°30′N and north of the Sub-Polar Front (SPF) were dominated by Sub-Arctic Intermediate Water (SAIW). CTD data combined with along-track continuous surface temperature and salinity measurements, satellite sea-level anomaly data and sea-surface temperature (SST) and along-track current data (ADCP data) showed that the position of the SPF was at about 52°N, at the southern edge of the Charlie–Gibbs Fracture Zone (CGFZ). South of the SPF a Frontal Region with both North Atlantic Central Water (NACW) and SAIW present was observed, and south of about 50°N the predominant water mass in the upper 500 m was NACW. A ship-mounted RDI 75 kHz ADCP was operated during the cruise and yielded high quality data during the first leg. The currents showed large variations over short distances and were strongly affected by topography. The ADCP data was be used to describe the mesoscale eddy field along the MAR and to detect three jets in the North Atlantic Current (NAC). Data from a current meter mooring left for 10 months after the cruise at a seamount just to the south of CGFZ showed the dominance of the tidal currents in the area. Typical spring tidal currents were about 0.15 m s−1 and the mean flow an order of magnitude smaller, about 0.03 m s−1. A short-term mooring on a seamount farther south showed tidal currents of 0.3 m s−1. Binned 8-day, 4-km SST satellite imagery were collected and processed for 2004. The SST data were analysed, and showed characteristic frontal structures in the MAR-ECO region.