The Northwest Tropical Atlantic Station (NTAS) : NTAS-4 mooring turnaround cruise report

Abstract

The Northwest Tropical Atlantic Station (NTAS) was established to address the need for accurate air-sea flux estimates and upper ocean measurements in a region with strong sea surface temperature anomalies and the likelihood of significant local air–sea interaction on interannual to decadal timescales. The approach is to maintain a surface mooring outfitted for meteorological and oceanographic measurements at a site near 15°N, 51°W by successive mooring turnarounds. These observations will be used to investigate air–sea interaction processes related to climate variability. Deployment of the first (NTAS-1), second (NTAS-2) and third (NTAS-3) moorings were documented in previous reports (Plueddemann et al., 2001; 2002; 2003). This report documents recovery of the NTAS-3 mooring and deployment of the NTAS-4 mooring at the same site. Both moorings used 3-meter discus buoys as the surface element. These buoys were outfitted with two Air–Sea Interaction Meteorology (ASIMET) systems. Each system measures, records, and transmits via Argos satellite the surface meteorological variables necessary to compute air–sea fluxes of heat, moisture and momentum. The upper 150 m of the mooring line were outfitted with oceanographic sensors for the measurement of temperature and velocity. The mooring turnaround was done on the NOAA ship Ronald H. Brown, Cruise RB-04-01, by the Upper Ocean Processes Group of the Woods Hole Oceanographic Institution. The cruise took place between 12 and 25 February 2004. The NTAS-3 buoy was found adrift and recovered on 19 February at 14°53.7’N, 51°22.8’W. Deployment of the NTAS-4 mooring was on 21 February at approximately 14°44.4’N, 50°56.0’W in 5038 m of water. A 30-hour intercomparison period followed, after which dragging operations to recover the lower portion of the NTAS-3 mooring commenced. This report describes these operations, as well as other work done on the cruise and some of the pre-cruise buoy preparations.