Description: The circulation of the northeastern Atlantic Ocean at intermediate depths is characterized by watermass transformation processes that involve Iceland–Scotland Overflow Water (ISOW) from the northeast, Labrador Sea Water (LSW) from the west, and Mediterranean Water from the south. Field observations were carried out with 89 eddy-resolving floats (RAFOS and MARVOR types). The data coverage achieved is remarkably high and enables a comprehensive study of the eastern basins between Iceland and the Azores. The trajectories show typical pathways of the water masses involved and the role that the complex bottom topography plays in defining them. The ISOW paths tend to lean against the slopes of the Reykjanes Ridge and Rockall Plateau. Westward escapes through multiple gaps in the ridge are possible, superimposed on a sustained southward flow in the eastern basin along the Mid-Atlantic Ridge. LSW pathways leading to the eastern basins are subject to high variability in flow direction and eddy activity. In addition to a selection of characteristic trajectories, maps of the horizontal distributions of Lagrangian eddy kinetic energy and integral time scales are presented. These reveal distinct areas of intensified mixing in the Iceland Basin, as well as the sharp contrast between the subpolar and subtropical dynamics. A self-contained eddy detection scheme is applied to obtain statistics on individual eddy properties and their abundance. It is suggested that much of the intensified mixing can be related to cyclonic activity, particularly in the subpolar region.

Description: It is becoming increasingly recognized that the eddy field plays an important—possibly dominating—role for oceanic motions in many aspects (e.g., transport of properties and risk assessment in the case of extreme events). This motivates the study of individual eddy events. In the Lagrangian coordinate system, vorticity possibly associated with eddies appears in two forms: as shear vorticity between neighboring particles, and as curvature of the trajectory of a single particle. Typical field experiments in physical oceanography using surface drifters or subsurface floats do not reach data densities high enough to produce enough encounters of drifters to calculate shear vorticity between them. However, curvature in individual tracks is easily observed. This study presents a methodology that extracts segments from within a trajectory that are “looping,” which will be interpreted as a drifter being caught in an eddy. The method makes use of autoregressive processes, a simple type of stochastic processes, which easily enables a fit to the nonperfectly shaped trajectory data usually expected from field experiments. These processes also deliver frequency and persistence of the detected eddies by a very simple calculation, which makes the methodology highly suited for automatized scanning of larger datasets.

Description: State of the climate in 2019

Description: 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 are used to investigate air–sea interaction processes related to climate variability. The NTAS Ocean Reference Station (ORS NTAS) is supported by the National Oceanic and Atmospheric Administration’s (NOAA) Climate Observation Program. This report documents recovery of the NTAS-14 mooring and deployment of the NTAS-15 mooring at the same site. Both moorings used Surlyn foam 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 160 m of the mooring line were outfitted with oceanographic sensors for the measurement of temperature, salinity and velocity. The mooring turnaround was done by the Upper Ocean Processes Group of the Woods Hole Oceanographic Institution (WHOI), onboard R/V Endeavor, Cruise EN573. The cruise took place between January 25 and February 13 2016. The NTAS-15 mooring was deployed on February 2, and the NTAS-14 mooring was recovered on February 4. A 24-hour intercomparison period was conducted on February 5, during which data from the buoy, telemetered through Argos satellite system, and the ship’s meteorological and oceanographic data were monitored while the ship was stationed 0.2 nm downwind of NTAS-15 buoy. A similar procedure was done at NTAS-14 but for only about 10 hours on the morning of February 4. This report describes these operations, as well as other work done on the cruise and some of the precruise buoy preparations. Other operations during EN573 consisted in the recovery and deployment of the Meridional Overturning Variability Experiment (MOVE) subsurface moorings array (MOVE 1 in the east, and MOVE 3 and 4 in the west near Guadeloupe). Acoustic download of data from Pressure Inverted Echo Sounders (PIES) was also conducted. MOVE is designed to monitor the integrated deep meridional flow in the tropical North Atlantic.

Description: Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA14OAR4320158.

Description: This cruise aimed to identify transport pathways from the surface into the interior ocean during the late winter in the Alborán sea between the Strait of Gibraltar (5°40’W) and the prime meridian. Theory and previous observations indicated that these pathways likely originated at strong fronts, such as the one that separates salty Mediterranean water and the fresher water in owing from the Atlantic. Our goal was to map such pathways and quantify their transport. Since the outcropping isopycnals at the front extend to the deepest depths during the late winter, we planned the cruise at the end of the Spring, prior to the onset of thermal stratification of the surface mixed layer.

Description: Funding was provided by the Office of Naval Research under Contract No. N000141613130.

Description: 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 are used to investigate air–sea interaction processes related to climate variability. The NTAS Ocean Reference Station (ORS NTAS) is supported by the National Oceanic and Atmospheric Administration’s (NOAA) Ocean Observing and Monitoring Division. This report documents recovery of the NTAS-16 mooring and deployment of the NTAS-17 mooring at the same site. Both moorings used Surlyn foam 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 160 m of the mooring line were outfitted with oceanographic sensors for the measurement of temperature, salinity and velocity. The mooring turnaround was done by the Upper Ocean Processes Group of the Woods Hole Oceanographic Institution (WHOI), onboard F/V Pisces, Cruise PC-18-03. The cruise took place between May 30 and June 21 2018. The NTAS-17 mooring was deployed on June 10, and the NTAS-16 mooring was recovered on June 12. No inter-comparison between ship and buoys was performed on this cruise. This report describes these operations, as well as other work done on the cruise and some of the pre-cruise buoy preparations. Other operations during PC-18-03 consisted in the recovery and deployment of the Meridional Overturning Variability Experiment (MOVE) subsurface moorings array (MOVE 1 in the east, and MOVE 3 and 4 in the west near Guadeloupe). Acoustic download of data from Pressure Inverted Echo Sounders (PIES) was also conducted. MOVE is designed to monitor the integrated deep meridional flow in the tropical North Atlantic.

Description: Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA14OAR4320158