Hydrographic Reanalysis

A hydrographic reanalysis reconstructs the historical three-dimensional ocean state from temperature and salinity profile observations, optimally interpolated or assimilated onto a regular grid over decades. It draws on the bottle, CTD, XBT, XCTD, and Argo float record, applying quality control, bias correction, and gap filling to produce gridded fields of temperature, salinity, density, and derived heat and freshwater content. Products such as the in-situ analyses behind GLORYS and the EN4 and World Ocean Atlas series anchor climate change estimates and serve as the observational constraint for ocean reanalyses. The sparse early record limits accuracy before the Argo era after 2005.