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In dem vorliegenden Beitrag werden Ergebnisse des Teilprojektes AMSeL_Ostsee A (03KIS0114) vorgestellt. Das primäre Ziel war die Ermittlung qualitativ hochwertiger Monatszeitreihen des mittleren Meeresspiegels (MSL) entlang der südwestlichen Ostseeküste sowie die anschließende Analyse der Zeitreihen zur Untersuchung der Langzeitentwicklung und der Variabilität auf unterschiedlichen Zeitskalen. Im Ergebnis konnten 49 MSL-Monatszeitreihen mit einer jeweiligen Zeitreihenlänge von 19 bis 185 Jahren generiert werden. Die Analysen zeigen über das 20. Jahrhundert von 1900 bis 2015 lineare Trends von 0,93 mm/a (Marienleuchte) bis 1,67 mm/a (Travemünde). Die Unterschiede zwischen den einzelnen Pegelstandorten beruhen auf Datenlücken, lokalen Effekten sowie vertikalen Landbewegungen (VLM – engl. vertical land motions). Mithilfe der Pegelzeitreihen, numerischen Modellläufen und Satellitenaltimeterdaten konnten verschiedene Einflussfaktoren auf unterschiedlichen Zeitskalen detektiert und quantifiziert werden. Werden die MSL Zeitreihen um relative Meeresspiegeländerungen aufgrund von postglazialen Landhebungen (GIA – engl. glacial isostatic adjustment) bereinigt, so ändern sich die linearen Trends nur geringfügig, da sich die südwestliche Ostsee im Übergangsbereich zwischen Landhebung und Landsenkung befindet. Für die gesamte südwestliche Ostseeküste ergibt sich für das 20. Jahrhundert (1900 bis 2015) anhand der GIA korrigierten Zeitreihen ein linearer Trend von 1,2 ± 0,1 mm/a. Dieser Wert liegt aufgrund der lokalen Beeinflussungen der südwestlichen Ostseeküste durch unterschiedliche Einflussfaktoren, wie insbesondere Veränderungen in den dominanten Westwindlagen, an der unteren Grenze derzeitiger Trendschätzer des GMSL von 1,3 bis 2 mm/a. Weiterhin zeigen die Untersuchungen eine kontinuierliche Beschleunigung in den Anstiegsraten, die immer wieder durch positive/negative Phasen interner Variabilität überlagert wird., This paper presents the results of the subproject AMSeL_Ostsee A (03KIS0114). The primary goal was the determination of high-quality monthly mean sea level time series (MSL) along the southwestern Baltic Sea coast and the subsequent investigation of long-term changes and variability. As a result, 49 MSL time series with a respective length of more than 19 years have been generated. The analyses show linear trends ranging from 0.93 mm/a (Marienleuchte) to 1.67 mm/a (Travemünde) at individual locations over the 20th century from 1900 to 2015. The differences between different sites result from a combination of data gaps, local effects (e.g. wind effects) and vertical land motions (VLM). To investigate the role of different forcing factors at various timescales the analysis of tide gauge records has been complemented with numerical model simulations and satellite altimetry data. After the adjustment of tide gauge records with estimates of relative sea level changes due to glacial isostatic adjustment (GIA), a linear trend of 1.2 ± 0.1 mm/a is found for the entire southwestern Baltic Sea coast. This value is at the lower limit of current trend estimates of the GMSL with 1.3 to 2 mm/a due to the local influences of various factors on the southwestern Baltic Sea coast, in particular changes in the prevailing westerly winds. Furthermore, our investigations point towards a sustained acceleration in MSL rates starting at the end of the 19th century, which is repeatedly interrupted by periods of pronounced internal variability., Ostsee, Pegelzeitreihen, MSL, Meeresspiegelanstieg, AMSeL_Ostsee, Baltic Sea, sea level time series, MSL, mean sea level rise, AMSeL_Baltic Sea

In diesem Beitrag werden die Ergebnisse des Teilprojektes MSL_Absolut-Rek (03KIS116) vorgestellt. Das prim��re Ziel bestand in der r��umlich-zeitlichen Rekonstruktion des mittleren Meeresspiegels (MSL) entlang der deutschen K��sten seit Beginn des 20. Jahrhunderts unter Ber��cksichtigung vertikaler Landbewegungen (VLM). Hierf��r wurde eine neuartige hybride Rekonstruktionsmethodik entwickelt, mit der der MSL global ��ber eine Kombination von Pegelbeobachtungen und bekannten regionalen Mustern einzelner beteiligter Prozesse zun��chst auf einem globalen Gitter ermittelt und anschlie��end in verfeinerter Aufl��sung an die deutschen K��sten transferiert wird. Im Ergebnis sind ��ber die Periode von 1900 bis 2015 relative MSL Felder in der gleichen r��umlichen Aufl��sung entstanden, in der Satellitendaten seit 1993 vorliegen. Die auf diese Weise regionalisierten MSL Felder sind sowohl konsistent mit Tidepegelbeobachtungen als auch mit den einzelnen zu Grunde liegenden physikalischen Prozessen. Dies erm��glicht in der Folge nicht nur die Ableitung der klimatisch induzierten relativen MSL Entwicklung, sondern auch die Bewertung potentieller anthropogener und isostatischer VLM sowie bisher nicht detektierter Nullpunktverschiebungen an einzelnen Standorten. Die Ergebnisse zeigen zwischen 1900 und 2015 etwas h��here relative MSL Trends entlang der deutschen Nordseek��ste (1,9���2 mm/Jahr) als an der deutschen Ostseek��ste (1,6 mm/Jahr), wobei die r��umlichen Differenzen ma��geblich durch eine Intensivierung und H��ufung von Westwindlagen begr��ndet sind. ��berlagert werden diese Entwicklungen durch VLM, die sich mit wenigen Ausnahmen in einem Bereich ��0,5 mm/Jahr bewegen. Hauptursache stellen hierf��r isostatische VLM infolge der letzten Vereisung dar, die aber lokal auch durch anthropogene Ursachen wie Gasentnahmen ��berlagert werden k��nnen., We present the results of the sub-project MSL_Absolut-Rek (03KIS116). The primary goal of the project was the spatial and temporal reconstruction of mean sea level (MSL) along the German coastlines since the early 20th century under the consideration of vertical land motion (VLM). A novel hybrid reconstruction approach has been developed, which first models MSL globally as a combination of tide gauge observations and a priori known regional patterns of certain contributing processes. Then the resulting fields are downscaled to the German coastlines. As a result, relative MSL fields with the same spatial resolution as provided by satellite data since 1993 have been produced over the period 1900-2015. The fields regionalize MSL in a way that they (i) optimally fit to changes observed by the global tide gauge network, and (ii) are consistent with certain physical processes. This provides not only the possibility of assessing climate-induced relative MSL changes along the entire coastlines but also facilitates the subsequent detection of potential anthropogenic and postglacial VLM as well as previously undetected datum shifts at individual locations. The results point towards slightly higher relative MSL trends along the German North Sea (1.9-2.0 mm/yr) than along the Baltic Sea coastline (1.6 mm/yr), whereby the spatial differences are suggested to be primarily driven by an intensification and increase in frequency of westerly winds. These relative MSL trends are locally superimposed by VLM, which are in most cases not larger than ��0.5 mm/yr. The major driving factor of VLM are postglacial rebound processes, which can be locally superimposed by anthropogenic factors such as gas withdrawals., Meeresspiegelanstieg, Tidepegel, Meeresspiegelrekonstruktion, vertikale Landbewegung, sea level rise, tide gauge, sea level reconstruction, vertical land motion

Organic matter production by cyanobacteria blooms is a major environmental concern for the Baltic Sea as it promotes thespread of anoxic zones. Partial pressure of carbon dioxide (pCO2) measurements carried out on Ships of Opportunity (SOOP) since 2003 have proven to be a powerful tool to resolve the carbon dynamics of the blooms in space and time. However, SOOP measurements lack the possibility to directly constrain the depth–integrated net community production (NCP) due to their restriction to the sea surface. This study tackles the resulting knowledge gap through (1) providing a best–guess NCP estimatefor an individual cyanobacteria bloom based on repeated profiling measurements of pCO2 and (2) establishing an algorithm to accurately reconstruct depth–integrated NCP from surface pCO2 observations in combination with modelled temperature profiles. Goal (1) was achieved by deploying state–of–the–art sensor technology from a small–scale sailing vessel. The low–cost and flexible platform enabled observations covering an entire bloom event that occurred in July and August 2018 in the Eastern Gotland Sea. For the biogeochemical interpretation, recorded pCO2 profiles were converted to CT*, which is the dissolved inorganic carbon concentration normalised to alkalinity. We found that the investigated Nodularia–dominated bloom event had many biogeochemical characteristics in common with blooms in previous years. In particular, it lasted for about three weeks, caused a CT* drawdown of 80 μmol kg−1, and was accompanied by a sea surface temperature increase of 10 °C. The novel finding of this study is the vertical extension of the CT* drawdown up to 12 m water depth. Integration of the CT* drawdown across this depth and correction for vertical fluxes permit a best–guess NCP estimate of ~1.2 mol–C m−2. Addressing goal (2), we combined modelled hydrographical profiles with surface pCO2 observations recorded by SOOP Finnmaid within the study area. Introducing the temperature penetration depth (TPD) as a new parameter to integrate SOOP observations across depth, we achieve a reconstructed NCP estimate that agrees to the best–guess within 10 %. Applying the TPD approach to almost two decades of surface pCO2 observations available for the Baltic Sea bears the potential to provide new insights into the control and long–term trends of cyanobacteria NCP. This understanding is key for an effective design and monitoring of conservation measures aiming at a Good Environmental Status of the Baltic Sea.

Fluid flows in the ocean have a strong impact on the growth and distribution of planktonic communities. In this case study, we applied a Lagrangian eddy detection and tracking tool and a transfer operator approach to data from a coupled hydrodynamical-chemical-biological model of the Western Baltic Sea and studied the effects of eddies on plankton in the blooming period March to October 2010. We investigated the residence times of water bodies inside these eddies, using a tracer analysis and found that eddies can act in two different ways: They can be transporters of an enclosed water body that embodies nutrients and the plankton community and export them from the coast to the open sea; and they can act as fluid dynamical niches that enhance the growth of certain species or functional groups by providing optimal temperature and nutrient composition.

The eastern Baltic cod stock is in distress, but the underlying mechanisms are still poorly understood. To improve the understanding of their behaviour and ecology, 1260 cod were internally tagged with data storage tags (DSTs) during 2016 to 2019, within the international project TABACOD. The cod were caught, tagged and released in the Baltic Sea off the coast of Denmark, Germany and Sweden. 15 of the cod recaptured so far spent more than 90 days at liberty. The DSTs recorded pressure and water temperature experienced by the cod. Given the characteristic bathymetry between adjacent Baltic basins and the recapture distribution of conventionally externally tagged cod (T-bar anchor-tags), we could distinguish different patterns depending on release location. We found a surprising variety in horizontal movements; however, between June and November, all tagged cod apparently spent time in the Bornholm Basin, a major spawning area of eastern Baltic cod. While cod released near Bornholm (Denmark) displayed localized behaviour and frequently went to the deep Bornholm Basin (stationary behaviour), most of the cod tagged in Hanö Bay (Sweden) and near Rügen (Germany) returned to their shallower release areas after spawning (migratory behaviour). Additionally to these horizontal movements, cod displayed distinct vertical movements, again varying between individuals. However, a clear twilight-triggered pattern emerged year-round: with the onset of sunset, cod swam to shallower water or rose in the water column (up to 30m within 30 minutes) and returned to deeper water at sunrise. These vertical movements resulted in temperature changes of up to 9.6°C during single excursions crossing the thermocline. The unexpected spatio-temporal dynamics challenge our present understanding of eastern Baltic cod ecology. Moreover, the extended use of shallow water areas and the open water column suggest that the present survey approach of the Baltic International Trawl Survey has an unknown bias

Coastal zones connect terrestrial and marine ecosystems forming a unique environment that is under increasing anthropogenic pressure. Rising sea levels, sinking coasts, and changing precipitation patterns modify hydrodynamic gradients and may enhance sea–land exchange processes in both tidal and non-tidal systems. Furthermore, the removal of flood protection structures as restoration measure contributes locally to the changing coastlines. A detailed understanding of the ecosystem functioning of coastal zones and the interactions between connected terrestrial and marine ecosystems is still lacking. Here, we propose an interdisciplinary approach to the investigation of interactions between land and sea at shallow coasts, and discuss the advantages and the first results provided by this approach as applied by the research training group Baltic TRANSCOAST. A low-lying fen peat site including the offshore shallow sea area on the southern Baltic Sea coast has been chosen as a model system to quantify hydrophysical, biogeochemical, sedimentological, and biological processes across the land–sea interface. Recently introduced rewetting measures might have enhanced submarine groundwater discharge (SGD) as indicated by distinct patterns of salinity gradients in the near shore sediments, making the coastal waters in front of the study site a mixing zone of fresh- and brackish water. High nutrient loadings, dissolved inorganic carbon (DIC), and dissolved organic matter (DOM) originating from the degraded peat may affect micro- and macro-phytobenthos, with the impact propagating to higher trophic levels. The terrestrial part of the study site is subject to periodic brackish water intrusion caused by occasional flooding, which has altered the hydraulic and biogeochemical properties of the prevailing peat soils. The stable salinity distribution in the main part of the peatland reveals the legacy of flooding events. Generally, elevated sulfate concentrations are assumed to influence greenhouse gas (GHG) emissions, mainly by inhibiting methane production, yet our investigations indicate complex interactions between the different biogeochemical element cycles (e.g., carbon and sulfur) caused by connected hydrological pathways. In conclusion, sea–land interactions are far reaching, occurring on either side of the interface, and can only be understood when both long-term and event-based patterns and different spatial scales are taken into account in interdisciplinary research that involves marine and terrestrial expertise. peerReviewed

The skill of the state-of-the-art ocean circulation models GETM (General Estuarine Transport Model), RCO (Rossby Centre Ocean model), and MOM (Modular Ocean Model) to represent hydrographic conditions and the mean circulation of the Baltic Sea is investigated. The study contains an assessment of vertical temperature and salinity profiles as well as various statistical time series analyses of temperature and salinity for different depths at specific representative monitoring stations. Simulation results for 1970–1999 are compared to observations from the Baltic Environmental Database (BED). Further, we analyze current velocities and volume transports both in the horizontal plane and through three transects in the Baltic Sea. Simulated current velocities are validated against 10 years of Acoustic Doppler Current Profiler (ADCP) measurements in the Arkona Basin and 5 years of mooring observations in the Gotland Basin. Furthermore, the atmospheric forcing datasets, which drive the models, are evaluated using wind measurements from 28 automatic stations along the Swedish coast. We found that the seasonal cycle, variability, and vertical profiles of temperature and salinity are simulated close to observations by RCO with an assimilation setup. All models reproduce temperature well near the sea surface. Salinity simulations are of lower quality from GETM in the northern Baltic Sea and from MOM at various stations. Simulated current velocities lie mainly within the standard deviation of the measurements at the two monitoring stations. However, sea surface currents and transports in the ocean interior are significantly larger in GETM than in the other models. Although simulated hydrographic profiles agree predominantly well with observations, the mean circulation differs considerably between the models highlighting the need for additional long-term current measurements to assess the mean circulation in ocean models. With the help of reanalysis data ocean state estimates of regions and time periods without observations are improved. However, due to the lack of current measurements only the baroclinic velocities of the reanalyses are reliable. A substantial part of the differences in barotropic velocities between the three ocean models and reanalysis data is explained by differences in wind velocities of the atmospheric forcing datasets.