WP A focuses on the mechanisms of sea level variability, primarily on processes leading to spatially highly inhomogeneous patterns of regional sea level change on time scales of up to 50 years.
WP A will provide a comprehensive understanding of the natural and anthropogenic factors governing regional sea level variability and its patterns, by incorporating oceanographic, geodetic and cryospheric research as well as addressing terrestrial hydrological contributions. In order to determine the origin of regional sea level changes at decadal to centennial time scales and the associated mechanisms on decadal time scales, WP A has also to address basin-scale to global data quality issues of in situ and satellite observations.
Results from WP A will provide knowledge of processes leading to past, present and future sea level changes and the associated uncertainties in projected components. Such information is required as a boundary condition for coastal systems and their change on decadal to centennial time scales. Output from WP A will feed directly both into WP B creating an improved knowledge base of coastal sea level change information on the selected study regions, and into WP C by providing regional climate information.
To provide an improved, detailed understanding of the dynamics and forcing functions of past, contemporary and future regional sea level variability and changes, a challenge exists to identify all key processes involved, which in turn, are geographically diverse.
For instance, the tropical Indo-Pacific is governed by steric changes associated with wind-driven ocean circulation dynamics, and modes of climate variability such as El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Indian Ocean Dipole (IOD), while trends at the North American and European coasts will also be affected by thermohaline processes. In addition, land motion and mass redistribution effects impacting the tropical Indo-Pacific (e.g. local land motion due to volcanic activity; groundwater or hydrocarbon extraction; sediment compaction; ocean-shelf ice interactions governing the Antarctic ice sheets) are different from those at the N. American and European coasts (post-glacial vertical motion; melting of the Greenland ice sheet).
Furthermore, in order to simulate and predict decadal to centennial coastal change, we need a comprehensive understanding of the anthropogenic factors superimposed to natural variability, since both govern regional sea level variability and serve as a boundary condition to coastal systems. This includes an improved reconstruction of the spatial patterns of regional sea level change, with particular emphasis on the decadal variability and trends during the last century.
Detailed uncertainty measures are essential in the coastal zone, but are missing from regional sea level projections. Progress in this regard clearly necessitates an integration of hitherto rather disparate strands of research. As an example, large uncertainties in solid-Earth and gravity models hinder determination of Earth's mantle viscosity structure and its response to the last deglaciation (GIA models). Consequently, reconstructed paleo-sea levels in coastal regions can deviate from the eustatic value by more than 20 m due to continental levering or hydroisostatic correction (e.g., Lambeck et al., 2002), with substantial variability due to the regional loading response, whereas this mechanism is negligible for many island sites (e.g. Jevrejeva et al., 2014). Moreover, the contribution of present and future terrestrial hydrology is also considered major to sea level projections over the next 50 years and beyond.
In recent years, satellite measurements in combination with the global ARGO profiling network have revolutionized the observational capabilities in this regard (e.g., Kusche et al., 2012). Nevertheless, various data quality issues still need to be addressed, which are essential for improving our understanding of sea level changes and their representation in model simulations. The GRACE (since 2002) and GOCE (2009-2013) missions enabled the computation of high-resolution geoid models, and began to allow deriving changes in ocean mass, however their full potential for regional to coastal sea level research has not still been reached. In combination with the new German-US GRACE-follow on mission (anticipated starting data 2017), a new view on satellite gravity and altimetry observations is required for any sea level effort.
WP A provides an integrated approach investigating changes in sea level due to changes in the ocean circulation and ice-sheet - sea level - solid Earth interactions. WP A utilizes a combination of analyses of historic and contemporary ocean observations, sea level reconstructions from geological archives, and global ocean models with enhanced process dynamics in relevant regions. Thus, in addition to regional phenomena, WP A further addresses aspects of a more global or generic nature.
In addition, research projects that fall within both the Research Areas A and B (WP A/B) are:
The work program of SeaLevel is structured in four basic topics, which are addressed by several working groups:
Coordinated by Universität Hamburg, Center for Earth System Research and Sustainability
