Sea-level change over the northern European continental shelf due to atmospheric and oceanic contributions

Abstract

Global mean sea level (GMSL) is a key indicator of climate change as it comprises information on different components of the climate system. However, despite its importance for climate and society, GMSL cannot be used for coastal adaptation policies because regional sea-level variations can significantly depart from the global average. Providing accurate estimates of sea-level rise is therefore one of the most important scientific issues that climate change poses, with a large impact for the human population as it is recognized as the main driver for changes in sea-level extremes, influencing the non-linear interactions between processes acting over different temporal and spatial scales in coastal areas.

This thesis addresses different aspects of the sea-level variability over the northern European continental shelf. Paper I uses gridded satellite altimetry data and adopts the jet clusters perspective of the winter-time atmospheric variability over the North Atlantic to reassess the contribution of local winds to the sea-level variability over the northern European continental shelf. By using the jet clusters, Paper I distinguishes itself from the existing literature since the jet clusters provide a physical description of the atmospheric variability in the North Atlantic.

Papers II and III focus on the steric and manometric components of the sea-level over the Norwegian section of the northern European continental shelf and on the sea-level observing system in the region. Paper II first evaluates a coastal altimetry dataset, reprocessed with the ALES-retracker, against the Norwegian set of tide gauges. After showing a good agreement between the two, it exploits the coastal satellite altimetry dataset to reassess the steric component of the sea level over the Norwegian shelf: the paper finds that the estimates of the steric component of the sea-level do not depend much on the choice of the tide gauges or satellite altimetry. Paper III evaluates the sea-level observing system along the Norwegian coast by assessing the ability of a satellite gravimetry mission, the Gravity Recovery and Climate Experiment (GRACE), and of a combination of satellite altimetry and hydrography to monitor manometric sea-level variations in the region. It then investigates the open-ocean contribution to the inter-annual manometric sea-level variations along the coast of Norway. It shows that, while commonly considered not reliable in the coastal region, GRACE captures the main features of the manometric sea-level change in the area, which on interannual and longer time scales can be attributed to along-slope winds and open-ocean steric changes. Therefore, GRACE can be used to analyze the manometric sea-level variability, such as in sea-level budget studies, especially in those areas of the coastal ocean where in-situ measurements are sparse.

Overall, by focusing on the northern European continental shelf due to its well developed sea-level observing system, this thesis has demonstrated the potential of remote sensing observations in improving our understanding of sea-level variability and change in the coastal ocean.