FIELDWORK -> March 2004

Cruise D277, D278 : First deployment of the monitoring array


The vertical density profiles provided by the moorings should allow an estimation of the vertical structure of the return flow compensating the surface branch of the MOC. This is an essential prerequisite to estimate the MOC and the related meridional heat transport.


Departed Santa Cruz de Tenerife, Tenerife, February 26, 2004
Arrived Freeport, Grand Bahama, March 16, 2004.

Departed Freeport, Grand Bahama, March 19, 2004
Arrived Freeport, Grand Bahama, March 30, 2004


Eight full-depth moorings were deployed. Three moorings were equipped with a McLane Moored Profiler (MMP) that takes approximately one CTD profile every other day. Profilers were used instead of individual, fixed-location CTD sensors to reduce the number of instruments that need to be calibrated.

It was decided to have several moorings near each boundary to obtain boundary current measurements through thermal wind, to improve the signal-to-noise ratio, and to provide failsafe redundancy in the array. Also, at each boundary, one conventional full-depth mooring was deployed with 14 fixed-depth CTDs to obtain vertical sampling throughout the water column.

While all moorings were equipped with CTDs, bottom pressure sensors, and current meters are placed on some moorings. These instruments give information about the depth-independent part of the MOC that is dominated by highly variable dynamics.

The presence of the Mid-Atlantic Ridge (MAR) complicates the endpoint monitoring of the MOC, because a pressure drop may exist across the ridge. Below the ridge crest, the sub-basins to the east and west have to be monitored separately. We use an MMP mooring on one side of the MAR and a conventional fixed depth CTD mooring on the other. There are also back-up fixed-depth CTD moorings that only reach to the ridge crest.

Additional moorings were deployed along the sloping continental shelves equipped with CTDs, bottom pressure recorders, and current meters. The length of these moorings was varied so as to obtain continuous observations at fixed depths. This created an alternative vertical sampling strategy that helped solve the bottom triangle problem. This process was the continuous analogue to the sampling strategy employed by Lynch-Stieglitz et al. (1999) who used density information inferred from foraminiferal oxygen isotope data.

In total 22 moorings have been deployed: 9 at the eastern boundary, 4 east and west of the Mid Atlantic Ridge and 9 at the western boundary. Figure 1 shows the approximate locations of the moorings.

Figure 1: Approximate locations of deployed moorings. The upper panels show a zoom of the western (left) and eastern (right) boundaries. The red crosses indicate the location of the moorings.

Further details about the structure of the mooring array and instruments used along the western boundary, Mid-Atlantic Ridge, and eastern boundary can be found by clicking on Figure 2.

Figure 2: Depth profile of the longitudinal track shown in Figure One.


Group photo at the end of Cruise D278
Attaching a CTD logger and glass buoyancy during deployment
Deploying the top of a mooring with subsurface steel buoyancy and current meter
Attaching a Sontek current meter and Seabird CTD to an inductive mooring
Deploying the top of a mooring
Just before anchor release and final part of a mooring deployment
Preparing to deploy a mooring