Sea level and vertical land movement

Oceans 2025: Theme 1, work package 1.9

An important indicator of the ocean's role in climate change, and a strong test of model capabilities, is the total volume and mass budget of the oceans. A significant component of the observed sea level rise is the transfer of water from the continents into the oceans, such as fresh water flux from melting glaciers and ice sheets. However, this increase in water in the oceans does not cause a uniform sea level rise. For example, the combination of the decrease in the gravitational potential and the crustal uplift due to mass loss from an ice sheet would cause an apparent sea level fall near that ice sheet. We aim to analyze the pattern of sea level variations to help identify the source of melt water flux.

Because the redistribution of water causes crustal deformations that are much more localized than the gravity perturbations, different observational techniques can be combined to better identify the sources of sea level rise. In addition to satellite altimetry which measures the sea surface, it is vital to understand the crustal motion across the U.K. and globally as measured by GPS, DORIS, SLR and VLBI, and the combination of the crustal and sea surface motion observed by tide gauges and absolute gravity. This study will involve understanding and developing a definitive map of land motion across the U.K.

Among the many causes of vertical land motion in the U.K. is the ongoing response of the Earth to the last Ice Age (post glacial rebound or PGR). This causes regions in Scotland, which were previously glaciated, to uplift, while southeast England is subsiding. In addition, PGR can significantly impact globally-averaged measures of sea level rise, such as those inferred from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. We will work, together with university partners, to understand the impact of PGR on sea level observations in the U.K. and globally.

To help determine whether sea level rise has accelerated since the 19th century, data archaeology will be used to supplement the currently available tide gauge records. It is also hoped that new techniques such as estuarine core analysis will produce long records in regions of the world where long tide gauge records do not exist.