Analysing the 100year sea level record of Leixões, Portugal

► The long-term historic sea level data from Leixões (Portugal) has been recovered. ► Estimated mean sea level trend is not in line with global MSL rise predictions. ► Observed sea levels are influenced by prevailing weather systems and local atmospheric pressure. ► Caution is needed using a single tide gauge as representative of regional sea level. A new data set from the tide gauge at Leixões (North–West Portugal) has recently been transferred from its paper format into a digital time series of hourly sea level values. By measuring sea level variations since 1890, this tide gauge station is one of the few in the world with over 100yr of digitised hourly records and the longest for the South West of Europe and Iberian Peninsula. This paper presents the procedures adopted to recover the Leixões sea level data from paper chart records as well as the data quality control and data editing methodologies. The mean rate of sea level change between 1906 and 2008 is −0.70±0.27mmyr−1, which does not agree with the global mean sea level rise of 1–2mmyr−1. No evidence for vertical land movement was found and Global Isostatic Adjustment influence on sea level, at this location, can be neglected. It is likely that prevailing weather systems in the North Atlantic, especially in the winter, and local atmospheric pressure, influence sea levels at Leixões. A further contribution is found from tides and surges. The evolution of the port cannot be ignored when trying to understand sea level change.