Global hydrographic variability patterns during 2003-2008

Monthly gridded global temperature and salinity fields from the near-surface layer down to 2000 m depth based on Argo measurements are used to analyze large-scale variability patterns on annual to interannual time scales during the years 2003-2008. Previous estimates of global hydrographic fluctuations have been derived using different data sets, partly on the basis of scarce sampling. The substantial advantage of this study includes a detailed summary of global variability patterns based on a single and more uniform database. In the upper 400 m, regions of strong seasonal salinity changes differ from regions of strong seasonal temperature changes, and large amplitudes of seasonal salinity are observed in the upper tropical and subpolar global ocean. Strong interannual and decadal changes superimpose long-term changes at northern midlatitudes. In the subtropical and tropical basin, interannual fluctuations dominate the upper 500 m depth. At southern midlatitudes, hydrographic changes occur on interannual and decadal time scales, while long-term changes are predominantly observed in the salinity field. Global mean heat content and steric height changes are clearly associated with a positive trend during the 6 years of measurements. The global 6-year trend of steric height deduced from in situ measurements explains 40% of the satellite-derived quantities. The global freshwater content does not show a significant trend and is dominated by interannual variability.