Two-dimensional reconstruction of the Mediterranean sea level over 1970–2006 from tide gage data and regional ocean circulation model outputs

Two-dimensional reconstructions of the Mediterranean sea level corrected for the atmospheric effects are proposed at monthly interval over the period 1970–2006 using 14 tide gage records and 33-year long (1970–2002) sea level grids from the NEMOMED8 regional ocean circulation model (NM8) and the PROTHEUS System Atmosphere–Ocean coupled model (PS). They are compared with a similar reconstruction using decade-long sea level grids from altimetry (Topex/Poseidon and Jason1) and a published reconstruction by Calafat and Gomis (2009). Tests with extra tide gages, not used in the computation, show that interannual variability is better captured when using long (33-year) spatial grids. In particular the NM8-based reconstruction reproduces better the sea level variability at all independent tide gages. An empirical Orthogonal Function decomposition of this reconstruction over 1970–2006 shows that the temporal curve of the two first modes are highly correlated with the North Atlantic Oscillation. We note in particular different behaviors over the 1970–1994 and 1994–2006 time spans. Results suggest that the North Atlantic Oscillation forcing modified the spatial patterns of the Mediterranean sea level around the year 1993 close to the date of occurrence of the Eastern Mediterranean Transient (a major change in the deep water formation of the Levantine and Ionian basin that occurred in the early 1990s).