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The Baltic Sea is a semi-enclosed sea and consists of brackish water with a salinity of about 7 g/kg. It sporadically experiences salt water inflow events through the Danish straits with strong inflows occurring once per year on average. An increase in mean sea level, which is expected to rise similarly to the projected global mean sea level (GMSL), impacts the dynamics of these salt water inflow events. Therefore, we use a regional setup of the ocean circulation model GETM spanning over the western Baltic Sea and having a spatial resolution of 600 meter to investigate the response of GMSL rise to inflow events during the years 1980 to 2015. As case study, the processes of a recent inflow event in December 2014 are additionally simulated with a model setup, using a horizontal resolution of 200 meter. It is analyzed how transports of volume and salt would differ, if GMSL would be one meter higher than present day sea level. Hence, a simulation is performed with the same model setup as the reference simulation, only the bathymetry of the model setup is deepened by one meter.The results of the reference model simulations are evaluated by comparisons with observations. For example, salinity and temperature at two stations located at the Darss Sill and in the Arkona Basin agree well. In addition, the volume transport through the Öresund, computed from sea surface height in Viken and Klagshamn, have a correlation of 0.96 with observations during the years 2014 and 2015 (nudging of sea surface height is applied at the model boundaries). A detailed analysis of the change in the physical processes with one meter GMSL rise will be presented. However, first analyses of the inflow event in December 2014, simulated with the 600m GETM model setup, show that the duration of this event did not change. However, the volume of high saline water (> 17 g/kg) in the Arkona Basin increased by about 10.7% during the inflow event. In addition, results show similar relative changes in volume and salt transport through the Danish straits (at Darss Sill and Drodgen Sill), and a less than 2% higher relative salt transport than volume transport when considering only the transports where salinity is greater than 17 g/kg. These results suggest a quite linear increase in salt inflow with increasing volume transport through the Danish straits during this inflow event. [ABSTRACT FROM AUTHOR]

In this contribution we present a comprehensive analysis of sea level data around the Baltic Sea from 1777 to the present with a focus on the southwestern part, concentrating on quantifying and understanding long-term trends and the influence of inter-annual and decadal variability. Our analysis focuses on a new monthly mean sea level (MSL) dataset, generated from a first time available compilation of high-resolution sea level measurements combined with already existing monthly MSL time series. Our final MSL dataset consists of records at 139 sites in the Baltic Sea with a temporal resolution of at least 19 years. Additionally, we analyze outputs of barotropic and baroclinic reanalysis runs from a 3D hydrodynamic numerical ocean model to quantify different meteorological and climatological processes contributing to the local sea level budget. Throughout the 20th century (1900 to 2015), an average linear trend for the whole Baltic Sea of 1.66 ± 0.14 mm/yr could be determined (corrected for the in the region dominant vertical land motion signal from Glacial Isostatic Adjustment). This is in principal consistent with current GMSL trend estimates (1.3 to 2 mm/yr) for the same period (Church and White 2006, Hay et al., 2015; Dangendorf et al., 2017) within their specific error bars. However, within the basin large differences in trends from different stations are found, which reach from minimum values in the southwestern part (0.94 ± 0.15 mm/yr in Kolobrzeg) to maximum values in the eastern Gulf of Finland (2.21 ± 0.32 mm/yr in Kronstadt). These differences can primarily be explained by an intensification of westerly winds and a decrease of atmospheric pressure over the 20th century pushing lowering MSL rates in the west and increasing them in the east. With our study we outline major existing knowledge gaps in understanding sea level change and variability in the southwestern Baltic Sea. A better understanding of the past and present development of the MSL provides the basis for deriving more reliable future projections of sea-level rise. Church and White (2006): A 20th century acceleration in global sea-level rise. In: Geophysical Research Letters, Jg. 33, 1, n/a. doi: 10.1029/2005GL024826.Dangendorf et al. (2017): Reassessment of 20th century global mean sea level rise. In: Proceedings of the National Academy of Sciences of the United States of America, Jg. 114, 23, 5946-5951. doi: 10.1073/pnas.1616007114.Hay et al. (2015): Probabilistic reanalysis of twentieth-century sea-level rise. In: Nature, Jg. 517, 7535, 481-484. doi: 10.1038/nature14093. [ABSTRACT FROM AUTHOR]

Insight into processes contributing to the onset and breakdown of stratificationenhances our understanding of the ecosystem dynamics of shallow seas. In theGerman Bight, a region of freshwater influence (ROFI), stratification is mainlyinfluenced by tidal mixing, fresh water river inflow and wind forcing. The physicalregime of the German Bight in the ROFI region switches between stably stratified tosemi-diurnal stratification. In order to investigate the processes contributing to thisvariability, a three dimensional high resolution numerical model is setup basedon the General Estuarine Transport Model (GETM). The model has a horizontalresolution of 300 m in the inner German Bight and incorporates 30 vertically adaptivelayers. The model results are first compared against observations, showing that the model is ableto reproduce the observed physical regime. The model results are then used to calculate theterms in a dynamic equation for the potential energy anomaly (φ). These termsinclude the horizontal advection, depth-mean straining, non-mean straining, verticaladvection and vertical mixing. The contribution of these processes to stratification isassessed under different conditions in the ROFI region. The results show that inthe semi-diurnal stratification condition, the depth-mean straining and horizontaladvection terms are the most important processes. Both of these processes are in phaseleading to stratified conditions during low water and mixed conditions during highwater. On the other hand, in the stably stratified condition, vertical advection is asimportant as depth-mean straining and horizontal advection. In this condition, thedepth-mean straining and horizontal advection are out of phase and therefore oppose eachother, while the depth-mean straining and vertical advection are in phase. Thisresults in minimum stratification (minimum φ) occurring at maximum ebb andmaximum stratification (maximum φ) occurring at slack after ebb (low water). [ABSTRACT FROM AUTHOR]