Deep and intermediate layer warming in the western Mediterranean: Water mass changes and heaving

Abstract

Temperature and salinity have increased in the Western Mediterranean Deep Water during the second half of the 20th century, but surprisingly, the two water masses contributing to its formation (Atlantic Water and Levantine Intermediate Water) show no clear warming trends, at least for the same period of time. Previous studies concerned with long term TS property changes in the Western Mediterranean had dealt with changes on isobaric surfaces. In this study we decompose these changes into their two natural contributions: Changes on isopycnal surfaces and changes induced by heaving (vertical displacements of density surfaces). This decomposition shows that LIW temperature and salinity have increased when changes on density surfaces are analyzed. The upward movement of deep layers has induced cooling on isobaric levels masking LIW temperature trends and underestimating deep layers temperature trends. Copyright 2009 by the American Geophysical Union.