Abstract. This study focuses on the improved estimation of mesoscale surface ocean circulation obtained by merging TOPEX/Poseidon (T/P) and ERS-1 and -2 altimeter measurements between October 1992 and May 1998. Once carefully intercalibrated and homogenized, these data are merged through an advanced global objective analysis method that allows us to correct for residual long wavelength errors and uses realistic correlation scales of ocean dynamics. The high-resolution (0.25 ø x 0.25 ø) merged T/P + ERS-1 and -2 sea level anomaly maps provide more homogeneous and reduced mapping errors than either individual data set and more realistic sea level and geostrophic velocity statistics than T/P data alone. Furthermore, the merged T/P + ERS-1 and -2 maps yield eddy kinetic energy (EKE) levels 30% higher than maps of T/P alone. They also permit realistic global estimates of east and north components of EKE and their seasonal variations, to study EKE sources better. A comparison of velocity statistics with World Ocean Circulation Experiment surface drifters in the North Atlantic shows very good agreement. Comparison with contemporary current meter data in various oceanic regimes also produces comparable levels of energy and similar ratios of northward and eastward energy, showing that the maps are suitable to studying anisotropy. The T/P + ERS zonal and meridional components of the mapped currents usually present comparable rms variability, even though the variability in the Atlantic is more isotropic than that in the Pacific, which exhibits strong zonal changes. The EKE map presents a very detailed description, presumably never before achieved at a global scale. Pronounced seasonal changes of the EKE are found in many regions, notably the northeastern Pacific, the northeastern and northwestern Atlantic, the tropical oceans, and the zonally extended bands centered near 20øS in the Indian and western Pacific Oceans and at 20øN in the northwestern Pacific. IntroductionIt is now generally admitted that at least two altimetric missions are needed to resolve the main space scales and timescales of the ocean circulation, in particular, However, merging multisatellite data sets is not an easy task. It first requires homogeneous and intercalibrated sea surface height (SSH) data sets. It is then necessary to extract consistent sea level anomaly (SLA) data from the different satellites. Finally, advanced interpolation techniques are needed to map SLA data onto a regular space/time grid. Gridded SLA data can be considered as a final merged product; they can be used directly for signal analysis and in comparison with numerical models and in situ measurements [e.g., Chao and Fu, 1995; Hernandez et al., 1995]. They may also be assimilated into ocean circulation models since they provide both data and associated error estimates at each grid point, although the assimilation of along-track data may be preferred for sophisticated assimilation schemes [Fukumori, 1995].Effective merging techniques have been developed at CLS Space Oceanograp...

The Atlantic Ocean overturning circulation is important to the climate system because it carries heat and carbon northward, and from the surface to the deep ocean. The high salinity of the subpolar North Atlantic is a prerequisite for overturning circulation, and strong freshening could herald a slowdown. We show that the eastern subpolar North Atlantic underwent extreme freshening during 2012 to 2016, with a magnitude never seen before in 120 years of measurements. The cause was unusual winter wind patterns driving major changes in ocean circulation, including slowing of the North Atlantic Current and diversion of Arctic freshwater from the western boundary into the eastern basins. We find that winddriven routing of Arctic-origin freshwater intimately links conditions on the North West Atlantic shelf and slope region with the eastern subpolar basins. This reveals the importance of atmospheric forcing of intra-basin circulation in determining the salinity of the subpolar North Atlantic.