The influence of the North Atlantic Oscillation on sea-level variability in the North Atlantic region

Abstract

Satellite altimeter (Topex/Poseidon, 1992–2001) and tide-gauge measurements are used to explore the relationship of the sea level of the North Atlantic and neighbouring seas and coastlines to the North Atlantic Oscillation (NAO). Altimeter measurements suggest significant gyre-scale influence of the NAO in the North Atlantic, but also stronger influences on the continental shelf and inland seas of Europe. A north–south dipole in sea-level anomaly consistent with a hydrostatic response to the NAO sea-level pressure dipole is evident, but there are also large non-hydrostatic effects. The strongest response on the European Shelf is in the southeastern part of the North Sea where sea level is positively correlated to NAO Index. The sea level in two semi-enclosed seas, the Baltic Sea positively and the Mediterranean Sea negatively, is also strongly influenced by the NAO. A weak negative correlation is apparent around the northeastern coastline of North America. These features are confirmed by contemporary coastal tide-gauge data, but the tide-gauge data also show that the influence of the NAO was weaker early in the Twentieth Century (20C) on parts of the Northwest European coastline. Inter-annual sea-level variability associated with fluctuations in the NAO are generally much larger than those associated with secular trends. Inferred multi-decadal fluctuations associated with the NAO are very substantial compared to the 15(±5) cm estimated for 20C global sea-level rise (Church, J.A., Gregory, J.M., Huybrechts, P., Kuhn, M., Lambeck, K., Nhuan, M.T., Qin, D. and Woodworth, P.L. (2001 Church J.A. Gregory J.M. Huybrechts P. Kuhn M. Lambeck K. Nhuan M.T. Qin D. Woodworth P.L. 2001 Changes in sea level. Chapter 11 of the Intergovernmental Panel on Climate Change Third Assessment Report pp. 639–694 Cambridge University Press Cambridge [Google Scholar]). Changes in sea level. Chapter 11 of the Intergovernmental Panel on Climate Change Third Assessment Report, pp. 639–694. Cambridge University Press, Cambridge.) and scenario forecasts for the 21C (˜50 cm). Therefore, the behaviour of the NAO in the next few decades will be a major regional factor in sea-level rise and coastal vulnerability in some European regions.