Regional differences of relative sea level changes in the Northwest Atlantic: Historical trends and future projections

Mean sea level is one of the most important indicators for climate variability and change. Here, we use tide-gauge data and satellite measurements to examine recent trends in the mean relative sea level (RSL) in the Northwest Atlantic. We then combine model output and satellite observations to provide sea level projections in the 21st century. The mean RSL trend based on historical tide-gauge data shows large regional variations, from 2 to 4 mm/yr (above the global mean RSL rise rate) in the southeast to -2 mm/yr in the northwest along East Canada. This spatial difference can to a large degree be attributed to that in the vertical land motion measured by the Global Positioning System (GPS). The combination of altimeter-measured sea level change with the GPS data can approximately account for tide-gauge measurements at most stations over 1993-2011. When the GPS data are used, the projected mean RSL rise between 1980-1999 and 2090-2099 ranges from 38 to 63 cm along the Scotia-Fundy and Newfoundland coasts and smaller along Labrador, the northern Gulf of St. Lawrence, and the St. Lawrence Estuary. In spite of considerable uncertainties the ocean steric and dynamical effect is the dominant contributor (35-70 cm) to the RSL rise along the Canadian east coast. The land-ice (glaciers and ice sheets) melt contributes to the RSL rise by 10-15 cm except at Nain where it is negligible. The effect of the vertical land uplift is large (40-50 cm) at Nain, Sept-iles and Rimouski, significantly reducing the magnitude of the RSL rise.