Decomposing Mean Sea Level Rise in a Semi-Enclosed Basin, the Baltic Sea

Abstract

We analyzed changes in mean sea level (MSL) for the period 1950–2015 using a regional ocean model for the Baltic Sea. Sensitivity experiments allowed us to separate external from local drivers and to investigate individual forcing agents triggering basin-internal spatial variations. The model reveals a basin-average MSL rise (MSLR) of 2.08 ± 0.49 mm yr−1, a value that is slightly larger than the simultaneous global average of 1.63 ± 0.32 mm yr−1. This MSLR is, however, spatially highly nonuniform with lower than average increases in the southwestern part (1.71 ± 0.51 mm yr−1) and higher than average rates in the northeastern parts (2.34 ± 1.05 mm yr−1). While 75% of the basin-average MSL externally enters the Baltic basin as a mass signal from the adjacent North Sea, intensified westerly winds and a poleward shift of low pressure systems explain the majority of the spatial variations in the rates. Minor contributions stem from local changes in baroclinicity leading to a basin-internal redistribution of water masses. An observed increase in local ocean temperature further adds to the total basinwide MSLR through thermal expansion but has little effect on the spatial pattern. To test the robustness of these results, we further assessed the sensitivity to six different atmospheric surface forcing reanalysis products over their common period from 1980 to 2005. The ensemble runs indicated that there are significant differences between individual ensemble members increasing the total trend uncertainty for the basin average by 0.22 mm yr−1 (95% confidence intervals). Locally the uncertainty varies from 0.05 mm yr−1 in the central part to up to 0.4 mm yr−1 along the coasts.

Likely and High-End Impacts of Regional Sea-Level Rise on the Shoreline Change of European Sandy Coasts Under a High Greenhouse Gas Emissions Scenario

“…In a similar way, the Baltic Sea projections are calculated using those of the North Sea. This procedure leads to an increase in the consistency of multi-model statistics compared to those relying on the CMIP5 models within the semi-enclosed basins [54,57,80] and is also more realistic with regard to the processes governing multi-decadal sea-level changes in these marginal seas [81][82][83]. Finally, our selection choice leads to an increase in the Mediterranean projections compared to previous assessments based on AR5 data.…”

Upwelling-induced trace gas dynamics in the Baltic Sea inferred from 8 years of autonomous measurements on a ship of opportunity

“…The model run covers the period from 1961 to 2019. For a detailed analysis of the model performance see Placke et al (2018) and Gräwe et al (2019). For the present run, we restarted the model in 2003, but changed the atmospheric forcing to the operational reanalysis data set of the German Weather Service (DWD), with a spatial resolution of 7 km and a temporal resolution of 3 h (Zängl et al, 2015).…”

“…The co-occurrence of episodic upwelling periods and dynamic trace gas patterns, and the combination of the presented eightyears data set of SOOP Finnmaid and of high-resolution models (Placke et al, 2018;Gräwe et al, 2019) allow us to investigate the influence of coastal upwelling on surface pCO 2 and cCH 4 in the Baltic Sea on a large spatial and temporal scale. In this study we are aiming at:…”

ICONGETM v1.0 – Flexible two-way coupling via exchange grids between the unstructured-grid atmospheric model ICON and the structured-grid coastal ocean model GETM

“…An efficient decomposition into subdomains offers high-performance computing on massively parallel systems for high-resolution and climate-scale simulations (e.g. Lange et al, 2020;Gräwe et al, 2019). For coupling to other models GETM already provides an interface to ESMF (Lemmen et al, 2018…”