DGFI participates in the IGS TIGA Project by i) operating continuously observing GPS stations at six tide gauges in the Atlantic Ocean and ii) processing a network of about sixty GNSS sites as a TIGA Analysis Centre. The weekly processing of this network results in a seven years time series of station coordinates starting in January 2000, and a multi year solution (DGF07P01-TIGA) of epoch station coordinates with linear velocities. The vertical velocities derived from GPS at coastal sites are analyzed together with sea level trends derived from tide gauge records to distinguish sea level variations from vertical crustal movements. This procedure is complemented by including the sea surface trend obtained from satellite altimetry in the marine areas surrounding the tide gauge sites. The absolute sea level trends derived from satellite altimetry data and from the combination of GPS positioning and tide gauge records are in a good agreement. These results should be applied to refer the local mean sea levels (which realize the reference level of classical height datums) to a global reference surface W0.