Analyses of sea surface height (SSH) records based on satellite altimeter data and hydrographic properties have suggested a considerable weakening of the North Atlantic subpolar gyre during the 1990s. Here we report hindcast simulations with high‐resolution ocean circulation models that demonstrate a close correspondence of the SSH changes with the volume transport of the boundary current system in the Labrador Sea. The 1990s‐decline, of about 15% of the long‐term mean, appears as part of a decadal variability of the gyre transport driven by changes in both heat flux and wind stress associated with the North Atlantic Oscillation (NAO). The changes in the subpolar gyre, as manifested in the deep western boundary current off Labrador, reverberate in the strength of the meridional overturning circulation (MOC) in the subtropical North Atlantic, suggesting the potential of a subpolar transport index as an element of a MOC monitoring system.

[1] There is an incomplete description of the middepth circulation and its link to the oxygen minimum zone (OMZ) in the eastern tropical South Pacific. Subsurface currents of the OMZ in the eastern tropical South Pacific are investigated with a focus at 400 m depth, close to the core of the OMZ, using several acoustic Doppler current profiler sections recorded in January and February 2009. Five profiling floats with oxygen sensors were deployed along 85°50′W in February 2009 with a drift depth at 400 m. Their spreading paths are compared with the model flow field from a 1/10°tropical Pacific model (TROPAC01) and the Simple Ocean Data Assimilation (SODA) model. Overall the mean currents in the eastern tropical South Pacific are weak so that eddy variability influences the flow and ultimately feeds oxygen-poor water to the OMZ. The center of the OMZ is a stagnant area so that floats stay much longer in this region and can even reverse direction. In one case, one float deployed at 8°S, returned to the same location after 15 months. On the northern side of the OMZ in the equatorial current system, floats move rapidly to the west. Most current bands reported for the near-surface layer exist also in the depth range of the OMZ. A schematic circulation flow field for the OMZ core depth is derived which shows the northern part of the South Pacific subtropical gyre south of the OMZ and the complicated zonal equatorial flow field north of the OMZ.

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Sea level anomalies measured by the altimeters aboard the TOPEX/Poseidon and ERS satellites for the periods 1993–2001 and 1997–2001, respectively, are used to investigate the eddy field in the subpolar North Atlantic and in the Labrador Sea. A quadratic correction of the obtained eddy kinetic energy (EKE) with respect to significant wave height is applied that led to an increased correlation between moored and altimetric EKE in the central Labrador Sea. The mean EKE field shows higher levels associated with the main currents and a strong seasonality in the Labrador Sea. The annual cycle of the EKE shows a propagation of West Greenland Current (WGC) EKE into the central Labrador Sea with a mean southward propagation speed of about 3 cm s−1, while the EKE maximum in the Labrador Current is well separated from the interior by local EKE minima. The interannual variability of the EKE in the Labrador Sea shows distinct regional differences. In the WGC region, strong early winter maxima are found during 1993 and 1997–1999. In the central Labrador Sea, maxima are found during March/April 1993–1995 and 1997. Variations in the annual cycle of the WGC EKE are observed: While there is a weak annual cycle in the WGC region during 1994–1996 with more continuous EKE generation, during 1997–2000, there is a strong seasonal cycle with maximum EKE during January and particularly low EKE during summer. The propagation of WGC EKE into the central Labrador Sea is enhanced during 1997–2000, leading to a long persistence of EKE in the central Labrador Sea. During 1993–1995 and 1997 the central Labrador Sea EKE almost instantaneously increased during March/April, followed, in the earlier years, by a relatively fast destruction of the winterly generated EKE.

Zonal wind anomalies in the western equatorial Atlantic during late boreal winter to early summer precondition boreal summer cold/warm events in the eastern equatorial Atlantic (EEA) that manifest in a strong interannual Atlantic cold tongue (ACT) variability. Local intraseasonal wind fluctuations, linked to the St. Helena anticyclone, contribute to the variability of cold tongue onset and strength, particularly during years with preconditioned shallow thermoclines. The impact of cold tongue sea surface temperature (SST) anomalies on the wind field in the Gulf of Guinea is assessed. It contributes to the northward migration of humidity and convection and possibly the West African monsoon (WAM) jump.