ИСТИНА

Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García (2015) On the causes of the differential mean sea level variations between the northern and southern hemispheres of the Earth. Workshop global and regional sea level variability and change. Mallorca Spain, 10-12 June 2015. Book of abstract. p.28. On the causes of the differential mean sea level variations between the northern and southern hemispheres of the Earth. Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García In the last decades, satellite altimetry has provided sea level data more densely distributed in space and time, with the consequent improvement of information with respect to the sea level observation series from historical tide gauge records. It is well known that sea level does not rise (or fall) uniformly all over the oceans, but follow complex patterns in space and time. Among the attempts of gathering the observed behaviour in few intuitive parameters, a candidate to consider are the variations restricted to some large chosen oceanic areas. Several studies have shown, e.g. differences in the secular trend of sea level variations between the northern and southern hemispheres of the Earth. In 2011 Barkin pointed an averaged trend of about 2.45 ± 0.32 mm / year sea level rise in the northern hemisphere, in contrast to a much lower average rate of 0.67 ± 0.30 mm / yr in the southern one. That estimation showed a clear difference of 1.78 mm / year between the N/ S hemispherical rates of sea level change. It is in good agreement with more recent determinations obtained from the coastal tide gauge observations, like those reported by Woppelman et al. in 2014, which included corrections for the vertical geodetic displacements of the stations. That observed behaviour has not been fully explained yet. Among the potential causes, we analyze the effects of the changes of the gravitational attraction of the core, which is not invariant but experiences changes of various reported origins. Among them, we consider here the shifting with respect to the centre of mass of the whole Earth, which was suggested by Barkin et al in 2008 and treated later in 2011. In that previous work it was shown that the displacement of the core relative to the mantle would generate a slow tide of inner origin, asymmetric with respect to the equator and thus redistributing the oceanic and atmospheric masses between the southern and the northern hemispheres. This dynamical effect can contribute to driving the observed distinct behaviour of mean sea level rates between the opposite northern and southern hemispheres and even to be a leading mechanism to an extent that must be assessed. Along with the fundamental core of the tide, we consider other phenomena that can produce secular changes in sea level. Factors as e.g. the role of the asymmetric arrangement of the continents in relation to the northern and southern hemispheres, and the ocean volume and its thermal expansion,have been also invoked in the literature as potential sources of differences in the regional behaviour of sea level variations.