Description: Two high-resolution hydrographic sections occupied during February, March 1989 in the western and eastern basins of the North Atlantic at 14.5N are combined to study the water mass structure and meridional mass and heat transports. Absolute velocities were determined using these data and an earlier section at 8N in a linear inverse analysis. Mass balance for several layers representing the main water masses in the region and a zero net divergence for the sum of geostrophic and Ekman transport between the two sections are assumed. Using the annual mean of Ekman transports (13.6 Sv, 14.5N), (15.2 Sv, 8N) based on the climatology by Isemer and Hasse (1985) the annual average fluxes for the sections at 8N and 14.5N have been calculated. For the annual mean the strength of the meridional overturning cell at 14.5N amounts to 15.9 Sv with an associated heat transport of 1.22 PW. A similar value can be obtained at 8N where the annual mean heat transport reaches 1.18 PW and the overturning cell measures 15 Sv. The total northward heat transport is strongly dominated by the wind-driven Ekman heat transport. 'In-situ' values of heat transport using the actual wind-driven transports for the respective months yield even higher estimates. Heat transport at 14.5N rises to 1.37 +/- 0.42 PW (February) and the maximum is now at the 8N section, 1.69 +/- 0.52 PW (May). Comparisons of our results with another tropical section at 11N occupied concurrently demonstrate the large variability in heat transport related to changes in the wind field. Due to extremely weak winds in the eastern Atlantic and a resulting low Ekman transport, the 'in-situ' value of heat transport through this section ranged between 0.30 +/- 0.18 PW and 0.59 +/- 0.18 PW depending on the value chosen for the Ekman transport. The lower of the two heat transport estimates results from calculations with the actual observed winds and the other using a monthly climatological mean. That even the computations with the climatological monthly mean give such a low heat transport points to additional changes in the baroclinic structures between 11N and 14.5N.

Description: Continuous current measurements at the 1000 m level were obtained in the central Canary Basin of the northeast Atlantic near 33°N, 22°W for 2398 days. Even with this very long time series no statistically significant mean current could be estimated at that level, because the energetic fluctuations are large compared to the weak mean. In the eddy scale range, i.e. at current fluctuations are scales between 47 and 455 days, a pronounced anisotropy between zonal and meridional components is apparent. For the first time in the subtropical North Atlantic gyre our data allow confirmation of the expected spectral decrease beyond the eddy scale peak in an eastern basin. With respect to future global experiments we wonder if our results from an eastern basin location are representative for the general circulation at mid-ocean sites?

Description: Two major water masses dominate the deep layers in the Mariana and Caroline Basins: the Lower Circumpolar Water (LCPW), arriving from the Southern Ocean along the slopes north of the Marshall Islands, and the North Pacific Deep Water (NPDW) reaching the region from the northeastern Pacific Ocean. Hydrographic and moored observations and multibeam echosounding were performed in the East Mariana and the East Caroline Basins to detail watermass distributions and flow paths in the area. The LCPW enters the East Mariana Basin from the east. At about 13°N, however, in the southern part of the basin, a part of this water mass arrives in a southward western boundary flow along the Izu–Ogasawara–Mariana Ridge. Both hydrographic observations and moored current measurements lead to the conclusion that this water not only continues westward to the West Mariana Basin as suggested before, but also provides bottom water to the East Caroline Basin. The critical throughflow regions were identified by multibeam echosounding at the Yap Mariana Junction between the East and West Mariana Basins and at the Caroline Ridge between the East Mariana and East Caroline Basins. The throughflow is steady between the East and West Mariana Basins, whereas more variability is found at the Caroline Ridge. At both locations, throughflow fluctuations are correlated with watermass property variations suggesting layer-thickness changes. The total transport to the two neighboring basins is only about 1 Sverdrup (1Sv ≡ 106 m3 s−1) but has considerable impact on the watermass structure in these basins. Estimates are given for the diapycnal mixing that is required to balance the inflow into the East Caroline Basin. Farther above in the water column, the high-silica tongue of NPDW extends from the east to the far southwestern corner of the East Mariana Basin, with transports being mostly southward across the basin.

Description: Time series of currents from an array of 22 subsurface moorings in the Canary and Iberian Basins of the North Atlantic are analyzed with respect to low-frequency variability. The record lengths are usually 1 to 2 years but almost 9 years (site KIEL276, 33N, 22W) in one case. Maximal energies are observed at periods between 50 and 500 days, and high-energy events are found from time to time. The 9-year long series indicates changes in currents with a 3-4 year period, primarily in the zonal component, and anisotropic energy distributions are found for both current components at periods around 200 days. The vertical structure can be well approximated by the barotropic and first-order baroclinic dynamical modes or by one empirical orthogonal function. The regional distribution of spectral properties indicates higher energies in frontal zones and in the neighborhood of the Canary archipelago. In general, the kinetic energy in the month-to-year variability is lower than in the western basins of the North Atlantic.

Description: To study the EasternBoundaryCurrentsystem off Northwest Africa in detail several CTD/ADCP-sections and long-term mooring work were carried out in the channel between Lanzarote and Africa. The observations are compared with a fine-resolution model, which was developed in the framework of the CANIGO project. The water masses, which are observed in this area, are characterised and classified in density ranges. The current field shows a high spatial and temporal variability with maximum velocities of about 35 cm/s. Seasonal means as well as currents averaged across the channel are only a few cm/s. In the surface water a steady southward flow in the middle of the channel indicates the CanaryCurrent in this area. During fall a strong northward current is observed close to the African shelf. Though the CanaryCurrent strengthens during summer and fall due to an increase of the trade winds, the transport in the channel decreases or turns northward during that time due to the enhanced poleward current at the eastern side. A northward undercurrent with a mean velocity of +2.3 cm/s is observed at the African slope in 950 m depth. The poleward transport of AAIW increases during fall and a strong influence of relatively fresh AAIW is observed during that time. Most of the observations fit well to the results of the CANIGO model, but the occurrence of MW at the bottom of the channel and the corresponding southward flow cannot be resolved by the model.