Tuesday, 20 August
15:30 – 17:00
De Geer lecture hall

Water exchange between the Baltic Sea Proper and the Åland Sea

Pekka Alenius, Finnish Meteorological Institute, pekka.alenius@fmi.fi

Kimmo Tikka, Finnish Meteorological Institute; Laura Tuomi, Finnish Meteorological Institute; Urmas Lips, Tallinn Technical University

We present hydrographic conditions in the Lågskär Deep between Baltic Proper and Åland Sea in context of water exchange between the Baltic Proper and Åland Sea. Our data consists of 128 CTD profiles from R/V Aranda and 15 sections across the trench and 9 along it with two gliders. We show how dynamic this small trench is with moving fronts and rapidly changing conditions.

Water exchange between the Baltic Sea Proper and the Bothnian Sea goes in great extent through Lågskär Deep and Åland Sea. The sill depths are ca. 55 m and 65 m. We aim to study how the waters from Baltic proper go to the Bothnian Sea and to see if there would be conditions where the deep waters of the Baltic Proper could flow to the Bothnian Sea. We conducted a field experiment with R/V Aranda in early May 2017 to the Northern Baltic Proper, Åland Sea, and Southern Bothnian Sea.

During the cruise, two Slocum G2 gliders operated in the Lågskär Deep. Finnish glider 'Uivelo' measured 15 times a section across the trench and Estonian glider 'Mia' 9.5 sections along the deep in 9 days. Aranda observed meteorology and measured 128 CTD profiles in the Lågskär and Åland Sea area. The sea was in the early spring state with crowing seasonal thermocline though the SST was still only 3.5 – 5.5°C. The 36 km long, 12 km wide and 150 m deep Lågskär trench turned out the be a very dynamic area with rapidly changing conditions, mass flows in both directions, and fast moving fronts. In general, the deeper saltier waters flow from the South and fresher waters from the North, as expected.

Dynamics of the Baltic Sea Straits via Numerical Simulation of Exchange Flows

Emil Vassilev Stanev, Helmholtz-Zentrum Geesthacht, emil.stanev@hzg.de

Johannes Pein, Helmholtz-Zentrum Geesthacht; Sebastian Grashorn, Helmholtz-Zentrum Geesthacht; Yinglong Joseph Zhang, Virginia Institute of Marine Science, College of William & Mary; Corinna Schrum, Helmholtz-Zentrum Geesthacht; Verena Haid, Helmholtz-Zentrum Geesthacht

The Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), which uses unstructured grids, is set up for the North and Baltic Seas. With a resolution of ∼100m in the narrow straits connecting the two basins, this model accurately resolves the inter-basin exchange. Validation against observations in the straits shows the model has good skill in simulating the transport and vertical profiles of temperature, salinity and currents. The timing and magnitude of the major inflow event in 2014–2015 is also realistically simulated. The analysis is focused on the two-layer exchange, its dependence on the atmospheric forcing, and dominant physical balances. The two-layer flows in the three connecting straits show different dependencies upon the net transport. The spatial variability of this dependence is also quite pronounced. The three-strait system developed specific dynamics, with time lags and differences between currents in the individual straits during inflow and outflow conditions. Analysis on the impact of resolution indicates that the performance of the model changes depending on whether the narrow parts of the straits are resolved with a resolution of 500m or 100 m. With this ultra-fine resolution, gravity flows and variability of salinity in deep layers is generally more adequately simulated. This paper identifies the needs for more profound analysis of the coupled dynamics of Baltic and North Seas with a focus on the Danish straits.

The Knudsen theorem and the Total Exchange Flow analysis framework applied to exchange flow in the Baltic Sea

Hans Burchard, Leibniz Institute for Baltic Sea Research Warnemünde, hans.burchard@io-warnemuende.de

Karsten Bolding, University of Aarhus; Rainer Feistel, Leibniz Institute for Baltic Sea Research Warnemünde; Ulf Gräwe, Leibniz Institute for Baltic Sea Research Warnemünde; Knut Klingbeil, Leibniz Institute for Baltic Sea Research Warnemünde; Parker MacCready, University of Washington; Volker Mohrholz, Leibniz Institute for Baltic Sea Research Warnemünde; Lars Umlauf, Leibniz Institute for Baltic Sea Research Warnemünde; Eefke van der Lee, Leibniz Institute for Baltic Sea Research Warnemünde

The Knudsen theorem for estuarine exchange flow and its generalization with resolution in salinity coordinates, the Total Exchange Flow (TEF) analysis framework, are reviewed here. Using the Knudsen theorem and the TEF analysis framework, validated multi-decadal (years 1949-2013) model simulations are analyzed in terms of exchange flow, including the reproduction of Major Baltic Inflows.

The Knudsen theorem for estuarine exchange flow, based on mass conservation of water and salt, and its generalization with resolution in salinity coordinates, the Total Exchange Flow (TEF) analysis framework, are reviewed here. The former had been developed, and applied to quantify exchange flow between the North Sea and the Baltic Sea, more than a century ago. Using the Knudsen theorem and the TEF analysis framework, validated multi-decadal (years 1949-2013) model simulations are analyzed in terms of exchange flow through straits of the Western Baltic Sea. The model-based long-term Knudsen and TEF analyses of exchange flow in the Western Baltic Sea reproduces the Major Baltic Inflows (MBIs) that have occurred since the 1950s. In addition, the recently discovered relationship between exchange flow and mixing in estuaries will be applied to the Baltic Sea, including the isohaline perspective.

The future of Gulf of Bothnia: Long term hydrodynamic and wave scenarios

Simo-Matti Siiriä, Finnish Meteorological Institute, simo.siiria@fmi.fi

Lars Arneborg, Swedish Meteorological and Hydrological Institute; Sam Fredrikkson, Swedish Meteorological and Hydrological Institute; Jari Haapala, Finnish Meteorological Institute; Jenny Hieronumys, Swedish Meteorological and Hydrological Institute; Robinson Hordoir, Institute of Marine Research; Anders Höglund, Swedish Meteorological and Hydrological Institute; Annu Oikkonen, Finnish Meteorological Institute; Jani Särkkä, Finnish Meteorological Institute; Laura Tuomi, Finnish Meteorological Institute

We have made hydrodynamic and wave model runs up to year 2059 for estimating the impacts of changing climate on Gulf of Bothnia. The models used are 1 nmi NEMO setup with LIm³ ice model and 1 nmi WAM for waves. Scenario runs are forced with several downscaled global climate models. This study is part of the SmartSea project, aiming to develop a plan for sustainable future for the Gulf of Bothnia.

As the climate changes, so will the Gulf of Bothnia. In addition to warming, the possible impacts include a shorter ice-season, changes in salinity, sea level, wave and current conditions. All this may significantly affect many activities within the area, including fishing, aquaculture and possibilities of wind parks, to name a few.

In order to estimate these impacts, we have made high-resolution hydrodynamic and wave model runs up to year 2059 with two different climate scenarios, RCP 4.5 and RCP 8.5. Our analysis of the scenarios concentrates especially on extreme events. Planning future activities in the Gulf of Bothnia requires knowledge of these, e.g. maximum ice loads for designing wind parks, or maximum temperature anomalies for aquaculture. The models used are 1 nmi NEMO setup with LIm³ ice model and 1 nmi WAM for waves. Scenario runs are forced with several downscaled global climate models. Hindcasts and historical scenario runs are compared to available measurements for estimating the quality of the setup. This study is part of the SmartSea project which aims to develop a plan for sustainable future for the Gulf of Bothnia.

Spring cold/saline intrusions in the Baltic Proper: in search of the mechanism for formation of the cold intermediate layer

Andrei Bagaev, Shirshov Institute of Oceanology, Russian Academy of Sciences, a.bagaev1984@gmail.com

Tatiana Bukanova, Shirshov Institute of Oceanology, Russian Academy of Sciences; Irina Chubarenko, Shirshov Institute of Oceanology, Russian Academy of Sciences

We examine a hypothesis of the formation of the Cold Intermediate Layer in the Baltic Proper. Joint analysis of field observations in the south-eastern part of the Baltic Sea (the Gdansk Bay) and remote sensing data on sea surface temperature is performed. We provide arguments that the intrusion waters observed in the Gdansk Bay were formed in the western part of the Bornholm Basin in March.

We examine a hypothesis of the formation of the Cold Intermediate Layer (CIL) in the Baltic Proper. Joint analysis of field observations in the south-eastern part of the Baltic Sea (the Gdansk Bay) and remote sensing data on sea surface temperature is performed. Time span is early spring (March-April), 2013. Intensification of cold-water intrusion activity in intermediate layers is a well-known every-spring phenomenon in the Baltic Proper, associated with seasonal transition from the two-layered winter density stratification to the three-layered summer stratification. These changes result from gradual arrival of slightly more saline intrusions at various depths in intermediate layers that have extremely low temperature. We provide arguments that the intrusion waters observed in the Gdansk Bay were formed in the western part of the Bornholm Basin in March. Remote sensing data for 2000-2019 demonstrate the regions with the coldest surface waters in early spring, their interannual variability (after cold/mild winters), and reveal potential sources of the observed intrusions. The research was supported by RFBR project №19-05-00717.

Salinity Dynamics of the Baltic Sea

Andreas Lehmann, GEOMAR, alehmann@geomar.de

Kai Myrberg, Finnish Environment Institute SYKE; Piia Post, Institute of Physics University of Tartu

Since BACC II which has been published in 2014, collecting mostly research results until 2012, there has been new research on the salinity dynamics of the Baltic Sea stimulated by Baltic Earth. We will present the current status of the Baltic Earth Assessment Report (BEAR) on Salinity Dynamics and will highlight some newly published results since BACCII.

The salinity in the Baltic Sea is not only a topic of physical oceanography, but it also involves the complete water and energy cycle. It is also a primary factor (driver) controlling the ecosystems of the Baltic Sea. The salinity dynamics is controlled by net precipitation, river runoff and the water mass exchange with the North Sea with outflow of the Baltic Sea due to freshwater surplus and a compensating inflow of higher saline waters from the Kattegat in deeper layers, strongly controlled by the prevailing atmospheric forcing conditions. First studies of future development indicate up to 2‐3 g/kg decrease in salinity due to the expected increase in precipitation to the end of the century. Since the Baltic Sea ecosystem has adapted to the present salinity regime, expected changes would exert enormous stress on marine fauna and flora with associated negative social-economic consequences for the Baltic Sea countries. Since BACCII there has been new research on the salinity dynamics of the Baltic Sea stimulated by Baltic Earth. We will present the current status of the Baltic Earth Assessment Report (BEAR) on Salinity Dynamics and will highlight some newly published results.

Wednesday, 21 August
11:15 – 12:45
De Geer lecture hall

Accumulation of recalcitrant autochthonous organic matter in eutrophic coastal environment

Eero Asmala, University of Helsinki, eero.asmala@helsinki.fi

Lumi Haraguchi, Aarhus University; Hans Jakobsen, Aarhus University; Stiig Markager, Aarhus University; Philippe Massicotte, Université Laval; Bo Riemann, Aarhus University; Peter Staehr, Aarhus University; Jacob Carstensen, Aarhus University

We characterized dissolved organic matter (DOM) pools in a eutrophic estuary over an annual cycle and carried out incubations to examine the processing of fresh autochthonous DOM. The results showed that autochthonous DOM from in situ production was rapidly transformed to more recalcitrant DOM that accumulated in the estuary, contributing significantly to transport of organic carbon to the ocean.

In coastal zones multiple biogeochemical processes remove, produce, and transform nutrients and organic matter transiting from land to sea. The extent to which coastal zones are merely a conduit for terrestrial organic matter versus a distinct source of autochthonous organic matter fueled by eutrophication is unclear. We characterized the coastal dissolved organic matter (DOM) pools in a eutrophic estuary (Roskilde Fjord, Denmark) over an annual cycle. We also carried out incubation experiments to examine the processing of fresh autochthonous DOM produced by coastal plankton communities. Multiple analytical approaches were used to obtain insights about the characteristics of the DOM pool. The results showed that labile autochthonous DOM from in situ primary production was rapidly transformed to more recalcitrant DOM that accumulated in the estuary. Accumulated DOM was characterized by low molecular size and stable carbon isotopic value and by high protein-like fluorescence. These results indicate that autotrophic material can be a major source of recalcitrant DOM in eutrophic coastal waters, contributing to the transport of organic carbon to the ocean.

Future acidification of the Baltic Sea – a sensitivity study

Erik Gustafsson, Baltic Nest Institute, Baltic Sea Centre, Stockholm University, erik.gustafsson@su.se

Bo G Gustafsson, Baltic Nest Institute, Baltic Sea Centre, Stockholm University

A coupled physical-biogeochemical Baltic Sea model is used to test the sensitivity of the carbonate system to changes in external forcing and also the internal cycling of organic matter. The aim is to determine how sensitive different sub-basins of the Baltic Sea are in terms of future acidification when climate and land loads change.

Future acidification of the Baltic Sea will depend on the development of atmospheric CO₂, but also on changes of carbonate system parameters such as the total alkalinity (TA). A coupled physical-biogeochemical Baltic Sea model is used to test the sensitivity of the carbonate system to changes in external forcing and also the internal cycling of organic matter. The experiments include for example changes in riverine TA loads, exchange between the Baltic and North Seas, and changes in nutrient loads. Potentially large changes in TA could emerge if e.g. precipitation and runoff increase in the boreal catchments but decrease in the continental limestone-rich catchments. Another area of interest is changes in nutrient loads and productivity, deep water oxygen concentrations, and oxygen dependent processes that either produce or consume TA. The aim of these experiments is primarily to determine how sensitive different sub-basins of the Baltic Sea are in terms of future acidification when climate and land loads gradually change, and further to determine what factors that exert the main control on acidification in the different sub-basins.

Diurnal cycle of the carbon dioxide in the Baltic Sea

Martti Honkanen, Finnish Meteorological Institute, martti.honkanen@fmi.fi

Jukka Seppälä, Finnish Environment Institute; Sami Kielosto, Finnish Environment Institute; Pasi Ylöstalo, Finnish Environment Institute; Timo Mäkelä, Finnish Meteorological Institute; Juha Hatakka, Finnish Meteorological Institute; Timo Tamminen, Finnish Environment Institute; Lauri Laakso, Finnish Meteorological Institute

The pCO₂ in the surface seawaters of the Baltic Sea is controlled by multiple processes. We will present one year of CO₂ partial pressure and flux measurements gathered in the Archipelago Sea. We separate the diurnal contribution of different processes on the pCO₂ during different seasons. Results indicate that highest variations in the seawater pCO₂ are observed in summer and autumn.

The exchange of carbon dioxide (CO₂) between the sea and the atmosphere is regulated by the CO₂ partial pressure (pCO₂) difference between the sea and the atmosphere. The pCO₂ in the surface seawaters of the Baltic Sea is controlled by multiple processes, such as the changes in temperature and salinity, sea-atmosphere exchange, biological activity and mixing of water masses. Many of these processes contain both the diurnal and annual variability. Research cruises and voluntary observing ships gather valuable information of the annual cycle of the pCO₂ in the Baltic Sea, which can be used for the calculation of the sea-air fluxes of CO₂. However, due to the diurnal variability of pCO₂, the time of the pCO₂ sampling affects the size of the calculated flux. We will present one year of CO₂ partial pressure and flux measurements gathered in the Archipelago Sea. We separate the diurnal contribution of different processes on the pCO₂ during different seasons. Results indicate that highest variations in the seawater pCO₂ are observed in summer and autumn, when the biological activity is strongest and the pCO₂ concentration difference between the surface layer and layers below are largest.

Enhanced surface concentrations and air-sea fluxes of methane and carbon dioxide in the Baltic Sea caused by coastal upwelling

Erik Jacobs, Leibniz Institute for Baltic Sea Research Warnemünde (IOW), erik.jacobs@io-warnemuende.de

Michael Glockzin, Leibniz Institute for Baltic Sea Research Warnemünde (IOW); Carolyn Graves, Centre for Environment, Fisheries and Aquaculture Science (Cefas); Ulf Gräwe, Leibniz Institute for Baltic Sea Research Warnemünde (IOW); Seppo Kaitala, Finnish Environment Institute (SYKE); Bernd Schneider, Leibniz Institute for Baltic Sea Research Warnemünde (IOW); Gregor Rehder, Leibniz Institute for Baltic Sea Research Warnemünde (IOW)

Upwelling of subthermoclinal water in the Baltic Sea increases the surface concentrations and affects the air-sea fluxes of CH₄ and CO₂. In our recent study based on 8 years of ferry-based measurements, we assess the importance of upwelling for the Baltic Sea greenhouse gas air-sea balance on a local and basin-wide scale by also considering interannual variability and the underlying processes.

Upwelling is a common phenomenon in the Baltic Sea. By upward advection of water from below the thermocline, upwelling events in summer lead to a temperature drop as well as increasing CH₄ and CO₂ concentrations in the surface water. The magnitude of upwelling-induced trace gas fluxes into the atmosphere in the Baltic Sea is currently poorly constrained.

Our recent study within the project BONUS INTEGRAL is based on 8 years of continuous surface water CH₄ and CO₂ measurements aboard the ferry Finnmaid, traversing the Baltic Sea between Travemünde (Germany) and Helsinki (Finland). Using core hydrographic parameters combined with wind and model data, we identify major upwelling areas and periods along the transect. We investigate the effect of upwelling on the surface concentrations of CH₄ and CO₂, the related fluxes to the atmosphere and their interannual variability. Furthermore, we study the relaxation of the upwelling temperature, CH₄  and CO₂ signals to gain a deeper process understanding. By comparing our findings to the larger seasonal CH₄  and CO₂ patterns, we assess the importance of upwelling for the Baltic Sea greenhouse gas air-sea balance on a local and basin-wide scale.

Effect of benthic animals on the phosphorus flux at the sediment-water interface in the eastern Gulf of Finland

Nadezhda Berezina, Zoological Institute RAS, nadezhda.berezina@zin.ru

Alexey Maximov, Zoological Institute RAS; Oksana Vladimirova, Russian State Hydrometeorological University

This study shows that the activity of benthic invertebrates influences nutrient cycling in well-mixed coastal or estuarine areas (Eastern Gulf of Finland). Activity in sediment of polychaetes (Marenzelleria spp) influence notably the direction of phosphate fluxes (release or uptake) depending on its abundance. Mobile amphipods, isopods can transfer phosphates between benthic and pelagic habitats.

This paper focuses on effects of benthic species on the sediment-water phosphate flux in the easternmost part of the Gulf of Finland. We estimated the total phosphate (P) fluxes, the benthic biomass in intact sediment cores and the P excretion by abundant benthic species at 4 sites during the Catamaran Centaurus-II Cruise (2015). The P flux was from -2890 to 1180 µmol/m² day. The significant positive correlations between P excretion and benthic biomass (especially Marenzelleria arctia and Monoporeia affinis) and negative between P flux and benthic variables were found. Excretory products may be important direct sources of phosphates in the Gulf of Finland. The total benthic excretion rate varied 320-3460 µmol/m² day; 79-98% of P were released by M. arctia. Activity in sediment of the polychaetes may influence notably the direction of phosphate fluxes (release or uptake) depending on its abundance. The negative P fluxes, or sedimentary uptakes, were recorded at a location with very high invasive polychaete biomass (40 g/m²). Mobile swimming organisms (amphipods, isopods) can enhance P mobilization from the sediment and transfer to pelagial facilitating pelagic algal production.

Trait-based insights in typical bioturbation patterns

Claudia Morys, Stockholm University, claudia.morys@gmail.com

Mayya Gogina, IOW; Karline Soetaert, NIOZ Yerseke; Michael Zettler, IOW; Martin Powilleit, University of Rostock; Tom Ysebaert, NIOZ Yerseke; Stefan Forster, University of Rostock

Gallery-biodiffusors (GB) and food supply have previously been determined as driving factors for non-local and local sediment mixing, respectively and, thus, for ecosystem functioning. This study supports these findings based on a large data set which was obtained during different seasons. We suggest that these relationships can be used as proxies for simplified bioturbation estimates.

Anthropogenic pressures have profound effects on marine and coastal ecosystems. It is important to understand ecosystem functions and to predict how they will change with human interferences. Gallery-biodiffusors (GB) and food supply have previously been determined as driving factors for non-local and local sediment mixing, respectively and, thus, for ecosystem functioning. In the literature, partly contrasting effects of seasonality on bioturbation activities have been reported. This study presents a large data set of bioturbation and macrofauna in the southwestern Baltic Sea which was obtained during different seasons. No common seasonal structures were found. However, supporting previous findings, a general pattern was detected showing an increase in the extent and intensity of non-local mixing from west to east. GB thereby plays a key role as indicated by 1) their increased abundance with decreasing salinity and 2) the strong relationship between non-local mixing intensities and the abundance of GB. Local mixing intensities decrease with increasing food availability. We suggest that these relationships can be used as proxies for simplified bioturbation estimates.

Wednesday, 21 August
14:00 – 15:00
De Geer lecture hall

Prediction of the eutrophication of the Baltic proper in the period 2020 - 2050

Anders Stigebrandt, Dept of marine Sci, Univ of Gothenburg, anders.stigebrandt@marine.gu.se

Ambjörn Andersson, Dept of marine Sciences, Univ of Gothenburg

The evolution of the phosphorus P concentration c in the surface layer in winter in the period 1950 – 2018 is described very well by a P budget model that includes the internal P loading from anoxic bottoms. The computed evolution of c until 2050 is presented and discussed for the case “business-as-usual” and for a case where the deepwater is kept oxygenated by a natural or man-made event.

In the 1950s a tipping point was crossed when the land-based phosphorus loading of the Baltic Sea LPS exceeded the maximally allowable supply so that deepwater anoxia developed in the permanently salt-stratified Baltic proper. This opened the internal phosphorus source IPS from anoxic bottoms that amplifies eutrophication. LPS culminated in the 1980s and at the present it has about the same value as in the early 1950s. Despite this, the observed winter total P (TP) concentration c in the 60 m thick surface layer still increases with the highest observed value in 2018, about 1 mmol m^-3, which is at least 3 times higher than c in the 1950s. Obviously, the evolution of c cannot be explained by the evolution of LPS. Here we show that the evolution of c in the period 1950 – 2018 is described very well by a time-dependent P budget model that includes the IPS. The computed evolution of c in the period 2020 - 2050 is presented and discussed for the case “business-as-usual” and for a case where the deepwater is kept oxygenated by a natural or man-made event.

Environmental management of oxygen; a new perspective using baseline respiration as a concept

Kevin Vikström, kevinvikstrom@hotmail.com

Ines Bartl; Jan Karlsson; Johan Wikner

Respiration is a key metabolic process in any ecosystem. However, respiration in the absence of contemporary primary production can influence an ecosystems sensitivity to hypoxia. This study obtains a first esimate of baseline respiration and discusses a new perspective on limited success of oxygen concentrations management by limiting eutrophication in area rich with allochthonous carbon.

Respiration is a key metabolic process in the marine environment that is usually assumed to be driven by phytoplankton production. However, respiration in the absence of contemporary phytoplankton production, termed baseline respiration, can influence the energetics of an ecosystem and its sensitivity to hypoxia. Direct studies of baseline respiration and its importance for coastal oxygen status are currently lacking largely due to a lack of clarity in the original definition. This study obtains a first estimate of baseline respiration in a sub-arctic estuary by modifying the original definition, determines its contribution to annual plankton community respiration and presents a novel way of understanding the basal energetic need of a coastal ecosystem. The four analytical methods used to define baseline respiration converged on an average rate of 4.2 mmol O2 m^-3 d-1 ± 0.1 (SE), corresponding to an annual contribution of 50 % of planktonic respiration on the basin scale. The results also form a new way of viewing environmental management of oxygen in ecosystems where allochthonous carbon interferes with the domination of phytoplankton produced carbon. 

Particle shuttling and oxidation efficiency of organic carbon – In situ sediment observations in contrasting brackish marine environments

Madeleine Nilsson, Univ Gothenburg, madeleine.nilsson@gu.se

Nils Ekeroth, Univ Gothenburg; Mikhail Kononets, Univ Gothenburg; Astrid Hylén, Univ Gothenburg; Lena Viktorsson, SMHI; Elin Almroth Rosell, SMHI; Per Roos, DTU; Anders Tengberg, Univ Gothenburg; Per Hall, Univ Gothenburg

Particle shuttling of particulate organic carbon along depth gradients in the Baltic Sea were revealed based on measurements of benthic fluxes and sediment accumulation rates. The efficiency of OC oxidation increased with increasing normalized water depth, which may be explained by the age of the uppermost sediment layer (0–2 cm), which was youngest at the deep accumulation bottoms.

Strong influence of particle shuttling along depth gradients in the Baltic Sea were revealed from an extensive data set of benthic organic carbon (OC) oxidation efficiencies (oxidation rate in relation to OC inventory in surficial sediment). The data set includes in situ lander measurements of benthic dissolved inorganic carbon (DIC) fluxes, and sediment accumulation rates in different depositional regimes in the Baltic Sea. With the exception of permanently oxic stations, we found a positive correlation between the DIC efflux and the normalized water depth (water depth/maximum water depth in the basin) in the Baltic Proper and Gulf of Finland. The DIC flux was not correlated with OC inventories in the upper reactive layer of the sediment. Instead, the efficiency of OC oxidation increased with increasing normalized water depth, which may be explained by the age of the uppermost sediment layer (0–2 cm), which was youngest at the deep accumulation bottoms. This finding was supported by the high content of fresh labile organic material at these sites, and is most likely explained by particle shuttling, i.e. resuspension and redistribution of POC from shallow to deeper bottoms.

Fine-grained sediment dynamics driven by dense bottom currents in the South-West Baltic Sea: Combination of oceanographic and geological data with numerical modelling

Lucas Porz, Helmholtz-Zentrum Geesthacht, lucas.porz@hzg.de

Wenyan Zhang, Helmholtz-Zentrum Geesthacht; Corinna Schrum, Helmholtz-Zentrum Geesthacht

Deposition of fine-grained sediment is key to our understanding of carbon budget and ecosystem functioning. We aim to describe the driving mechanisms of large-scale morphodynamics in the SW-Baltic. A numerical model is used to simulate a dense water inflow that may rework and transport large amounts of material. A preliminary comparison with geological and oceanographic data is presented.

Fine-grained sediment deposits in the Baltic Sea basins act as a sinks for organic matter and contaminants. The goal of this study is to describe the driving mechanisms of large-scale mud deposition in the South-Western Baltic.

Budget calculations show that the majority of mud found in the SW-Baltic originates from the eroding soft cliffs of the bordering states, and riverine input accounts for only ~10% of the mass. A large portion of material may also be transported and reworked by bottom current activity during Major Baltic Inflows (MBI). Geological data suggest that episodic bottom currents play a key role in the morphodynamics in this area.

We set up and validate and unstructured ocean model to simulate the impact of the 2014 MBI on the morphology of the Arkona and Bornholm Basins. The model simulations show the detailed pathways of dense water entering the study area from the Kattegat. Marine seismic profiles display the temporally integrated impact of these events, resulting in intriguing sedimentation patterns.

Our study emphasizes the importance of a holistic approach to understanding sediment transport by combination of geological, oceanographic and numerical methods.

Posters, session 3A

Tuesday, 20 August
17:00 – 19:00
Aula Magna floor 5

Microplastics discharge from sanitary sewer overflow events

Christian Baresel, IVL Swedish Environmental Research Institute, christian.baresel@ivl.se

Mikael Olshammar, IVL Swedish Environmental Research Institute (presenter)

Discharge of microplastics from Sanitary sewer overflow (SSO) can be in the same magnitude as from treated wastewater, although the total flow is much lower than that of treated wastewater. SSO events frequently occur and are expected to increase due to climate change and urbanization, unless infrastructure is rebuild. It is therefore important to put focus and increase knowledge on this matter.

This contribution focus on the quantification of microplastics discharge from wastewater treatment plants (WWTPs) and Sanitary sewer overflow (SSO) to the Baltic Sea based on publicly accessible databases. The data was gathered and compiled within the BONUS project Micropoll.

When considering SSO three different kinds of overflows are considered: (i) sewer overflows caused by technical failures; (ii) Storm event SSO; and (iii) SSO treatment at WWTPs, comprises overflows due to a hydraulic capacity limitation of the WWTP but where the discharged water at least undergoes a partial treatment.

SSO is a category often neglected in conventional wastewater handling, as pollutant concentrations normally are much lower due to dilution with storm water. For MP, however, this does not have to be the case. Considering an increase of MP-concentrations in wastewater at SSO events as reported in literature, storm event SSO contribute substantially to total MP-discharge, here with more than 50%. Even if no changed concentration is considered, real SSO events account almost for 1/5 of the total MP-discharge to the Baltic Sea.

Dynamics of Natural Bromoanisoles in Northern Baltic Estuaries

Terry Bidleman, Umeå University, terry.bidleman@umu.se (presenter)

Agneta Andersson, Umeå University; Sonia Brugel, Umeå University; Peter Haglund, Umeå University; Olle Nygren, Umeå University; Mats Tysklind, Umeå University

Bromoanisoles (BAs) are formed by O-methylation of bromophenols (BPs), which are produced by macroalgae. and cyanobacteria. Concentrations ∑BAs in seawater were higher in four estuaries of the Bothnian Sea (325-919 pg l^-1) than at two offshore stations (142-430 pg l^-1) during spring-summer 2018. Monthly variations differed for 2,4-dibromoanisole (2,4-DiBA) and 2,4,6-tribromoanisole (2,4,6-TriBA).

Bromoanisoles (BAs) are formed by O-methylation of bromophenols (BPs), which are produced by marine macroalgae. and cyanobacteria. Both bioaccumulate in invertebrates and fish. We measured 2,4-dibromoanisole (2,4-DiBA) and 2,4,6-tribromoanisole (2,4,6-TriBA) in seawater of four estuaries and at two offshore stations in the Bothnian Sea during late May-early June, mid-July, mid-August and early September of 2018. Concentrations of 2,4-DiBA (63─457 pg l^-1) and 2,4,6-TriBA (157─768 pg l^-1) were higher in estuaries than offshore (43─120 and 86─311 pg l^-1, respectively) Monthly variations in the estuaries were different for the two compounds; 2,4-DiBA peaked in mid-July while 2,4,6-TriBA was higher in spring and September than in midsummer. Offshore concentrations were steady over most of spring-summer, rising slightly in September. Similar concentrations were found in August at the island Holmön, where 2,4-DiBA and 2,4,6-TriBA were 340 and 400 pg l^-1 in a shallow strait with visible macrophytes vs. 53 and 102 pg l^-1 offshore. Dynamics of the BAs are likely due to macrophyte populations, phytoplankton productivity, rates of formation and degradation, and estuarine-offshore water mixing.

Seasonal evolution of the spring bloom in the Gotland Deep in the years 2013-2018

Henry Bittig, IOW, henry.bittig@io-warnemuende.de (presenter)

Laura Tuomi, FMI; Gregor Rehder, IOW; Simo Siiriä, FMI; Bernd Schneider, IOW

The spring phytoplankton bloom accounts for a significant portion of marine biomass production and carbon fixation. Here, we use observations from BGC-Argo floats and from the ICOS VOS Finnmaid to find common patterns and differences in the 2013-2018 advent, evolution, and decay of the spring bloom and summer situation. The aim is to better understand mechanisms and relevant driving factors.

The spring phytoplankton bloom accounts for a significant portion of marine biomass production and carbon fixation. Upon decay, it causes a considerable export of organic matter below the surface mixed layer and fuels mesopelagic and benthic systems. In the Baltic Sea, the Gotland Deep is one of the most intensively and well-studied areas. Here, we add to these works the timing and subsurface progression of the spring bloom and its transition towards summer conditions using observations from BGC-Argo floats by Argo Finland and from the ICOS voluntary observing ship (VOS) Finnmaid. The BGC-Argo floats provide weekly water column data of phytoplankton (Chl a fluorescence) and net production proxies (O2), whereas the VOS line gives surface CO₂ observations every 2 days. These are used, together with regular monitoring data, to find common patterns and differences in the 2013-2018 advent, evolution, and decay of the spring bloom and summer situation. The aim is to better understand the mechanisms, to identify relevant driving factors as well as their interplay / dominance to improve process understanding and eventually regional ecosystem models.

Does bottom trawling release contaminants from sediments to the water column?

Clare Bradshaw, Stockholm University, clare.bradshaw@su.se (poster)

Baltic Sea sediments are a sink for a range of contaminants, but also support benthic fisheries using bottom trawling, an activity that is known to disturb the seafloor and suspend bottom sediments. The potential release of contaminants from sediment to the water by bottom trawling is poorly understood; this study presents new data from a field study addressing this question in the Bornholm Basin

Bottom trawling for benthic species such as cod and flatfish is known to disrupt benthic ecosystems and suspend bottom sediments. However, the resuspension of potentially contaminated sediments, and the resulting release of buried contaminants to the water column, is poorly understood. Baltic Sea sediments are known to be a sink for a large range of different contaminants that have accumulated over the last 50 years or more. At the same time, there is a locally intensive commercial fishery that uses bottom trawling to catch its target species.

In a previous study in a contaminated Norwegian fjord we used passive samplers attached to a bottom to demonstrate an order of magnitude increase in freely dissolved PCCD/F concentrations in the bottom water within minutes of the sediment being resuspended by bottom trawling. In this study, we used the same approach in the southern Baltic Sea to quantify release of organic contaminants (e.g. dioxins, PCBs) and metals from sediments in the Bornholm Basin, where there is a commercial demersal fishery for cod.

Iron speciation in sediments of the Gdańsk Basin (Southern Baltic)

Olga Brocławik, University of Gdańsk, olga.broclawik@onet.pl (presenter)

Katarzyna Łukawska-Matuszewska, University of Gdańsk; Aleksandra Brodecka-Goluch, University of Gdańsk

We found that iron mediated anaerobic methane oxidation (AOM) strongly impacts sedimentary iron cycling in the Gdańsk Basin. Iron dependent AOM leads to the consumption of iron oxyhydroxides. In addition, ferrous iron released in the process precipitates as carbonate minerals.

The aim of this study was to determine the influence of methane presence on iron speciation in sediments of the Gdańsk Basin. Sediment cores were collected in 2015-2017 from three sites: two where methane was found (P1, MET2) and one where it was absent (W6). Concentrations of the following iron species: carbonate-associated; easily reducible oxides (ferrihydrite, lepidocrocite); reducible oxides including goethite, hematite; magnetite; poorly reactive sheet silicate and pyrite; were investigated using the sequential extraction. Additionally, concentrations of total iron and methane in sediment were determined. Pore water was also collected and analyzed for vertical profiles of hydrogen sulphide and sulphate. The highest total iron concentration was observed on the deepest P1 station. At the W6, surface sediment layer was rich with iron oxyhydroxides, while at MET2 low concentration of iron oxyhydroxides and high of carbonates were observed. This is due to the reduction of Fe during anaerobic methane oxidation and the precipitation of ferrous with carbonates. This study was financed by the Polish National Science Centre (UMO-2013/11/B/ST10/00322; UMO-2016/21/B/ST10/02369).

Temporal and spatial variations of methane concentration in sediments of the Gdańsk Basin (Southern Baltic) over a period of 10 years (2009-2019)

Aleksandra Brodecka-Goluch, University of Gdańsk, Institute of Oceanography, a.brodecka@ug.edu.pl (presenter)

Katarzyna Łukawska-Matuszewska, University of Gdańsk, Institute of Oceanography; Damian Jaśniewicz, Institute of Oceanology, Polish Academy of Sciences; Jerzy Bolałek, University of Gdańsk, Institute of Oceanography

In the present study we investigated temporal and spatial changes in methane concentration in sediments of three environmentally different sites of the southern Baltic Sea. In the coastal area, methane content of sediments significantly decreased over 8 years and the sulfate-methane transition (SMT) moved down the sediment.

Continental shelf seas are considered the key regions in terms of methane production in marine sediments. Methanogenesis is strongly related to eutrophication of the marine environment. The objective of this study was to estimate the changes in methane concentration in sediments of three environmentally different areas of the southern Baltic Sea: 1) coastal region of the Bay of Puck, 2) pockmark area of the central Gulf of Gdańsk, and 3) stratified deepwater site within the Gdańsk Deep, over a period of 2009-2019. The most pronounced variations were observed for the coastal area. It turned out that in some sites methane concentration in surface (0-40 cm) sediments decreased by about 50% in 8 years. Moreover, the sulfate-methane transition (SMT) moved down the sediment and both DIC and ammonia concentrations were reduced, which points to the effect of lower supply of dead organic matter to the bottom. The spatial range of methane-bearing sediments also changed, e.g. one of the pockmark structures significantly developed. This study was financed by the Polish National Science Centre (UMO-2016/21/B/ST10/02369).

An autonomous profiler for extended monitoring and sampling of the turbulent benthic boundary layer

Jonas Fredriksson, Stockholm University, jonas.teddy.fredriksson@gmail.com

Julia Steinbach, Stockholm University (presenter); Volker Brüchert, Stockholm University

The marine benthic boundary layer provides a critical ecosystem function and controls the net exchange of carbon, nutrients, and gases between sediment and seawater. We deployed a lander system that resolves the temporal chemical and physical dynamics in this water layer. First data from a station in the Trosa archipelago indicate substantial episodic and temporal variability in this water layer.

Coastal and shelf sediments exchange particles, solutes, and gases with the overlying water through the turbulent benthic boundary layer (BBL), the commonly several decimeter-thick water layer above all sediments. Processes in the BBL have been suggested to provide key ecosystem functions, but few studies have investigated the temporal biogeochemical dynamics in the BBL. We show how this environment can be sampled using a profiling, autonomous benthic lander system for extended time periods up to one month. The lander has a programmable vertical sliding stage with a sensor package that records time series of salinity, temperature, oxygen, turbidity, fluorescence, and PAR. An ADCP obtains a current profile over the bottom 50 cm above the sediment surface and an underwater video camera system records the benthic environment. A peristaltic pump collects individual water samples from 12 depths for chemical analysis or incubation studies. We show that the system records substantial episodic and periodic changes over minutes to hours in the hydrographic and chemical state of the BBL in a coastal environment at 27 m water depth in the Trosa archipelago.

Some characteristics of air temperature variations over coastal waters of the south-eastern Baltic Sea for 2004-2017

Zhanna Stont, Shirshov Institute of Oceanology, Russian Academy of Sciences, ocean_stont@mail.ru

Tatiana Bukanova, Shirshov Institute of Oceanology, Russian Academy of Sciences (presenter)

The climate of the study area has become more marine. The air temperature is higher than in the 20th century, and rises at a rate of 0.005 °C/month. The lower values of the NAO cause the decrease of air temperature. The NAO's positive phase leads to the air temperature increase. The slowdown of air temperature rise is caused by enhancement of the eastern form of circulation by Wangenheim-Girs.

The study of air temperature variability in the south-eastern Baltic Sea uses the data from the automatic hydrometeorological station located 20 km from the coast on the offshore ice-resistant fixed platform. The annual mean air temperature is 8.8 ± 0.6 ºС, which is 1.4 ºС higher than in the middle of the last century. The annual minimum of air temperature has shifted towards February, therefore the climate of the south-eastern Baltic Sea has become more marine. The rate of monthly mean air temperature increase is 0.005 °C/month. A close relationship between the North Atlantic Oscillation (NAO) index and the air temperature is shown (correlation coefficient r = 0.7). The lower values of the NAO stipulate the intensification of anticyclonic activity and the decrease of air temperature in the study area. The predominance of a positive phase of the NAO causes the strengthening of the Icelandic Low and a west-east transfer what results in the air temperature rise. The enhancement of the eastern form of circulation by Wangenheim-Girs induces the slowdown of the air temperature increase in the study area. The study was done with a support of the state assignment № 0149-2019-0013.

Microplastic load in Baltic Sea invertebrates

Aymeric Chancel, Stockholm University, chancel.aymeric@gmail.com (presenter)

Ekaterina Gutovskaia, Stockholm University; Lisa Winberg von Friesen, IVL Swedish Environmental Research Institute; Evelyne Hamacher-Barth, Stockholm University; Elena Gorokhova, Stockholm University

Microplastic is recognized as an emerging contaminant in aquatic environments. Standard methods for the extraction of microplastics from biota are currently lacking. We report a method optimization for extracting microplastics from pelagic and benthic invertebrates collected in the Baltic Sea.

Microplastic (MP) is recognized as an emerging contaminant in aquatic environments. To understand the MP fate in the system, we need efficient screening methods applicable to different ecosystem components. Standard methods for the extraction of microplastics from biota are currently lacking, and most methods employing strong acids can also degrade the polymers. Here, we report a method optimization for extracting microplastics from crustaceans using pancreatic enzymes and amphipods Monoporeia affinis as a test species. Further, the method was applied to a range of pelagic and benthic invertebrates collected in the Baltic Sea. To identify MP, the digested samples were stained with Nile Red and pre-screened using a fluorescence microscope. The putative MP were analysed using micro-FTIR. The method optimization and data on MP occurrence will be presented and discussed.

Coastal-marine solute spreading from different Baltic coastlines

Yuanying Chen, Stockholm University, yuanying.chen@natgeo.su.se (presenter)

Vladimir Cvetkovic, Royal Institute of Technology; Georgia Destouni, Stockholm University

We simulate solute release-spreading scenarios in different Baltic coast cases. Results show similar concentration spreading into the sea for similar (diffuse or large-river) loading from land in different coastal flow situations. For nutrients, loading from land differs substantially between total and per-capita terms, with fairness implications for requirements of per-capita load reductions.

The Baltic Sea suffers from eutrophication largely due to the loading of waterborne nutrients from land. In this study, we compare solute release and spreading scenarios for two different types of coastal load and spreading cases: (1) the Swedish Kalmar County coastline with diffuse loading and further flow-transport largely along the coastline; and (2) the coastal outlet of the Vistula River in Poland, with large river loading and flow-transport largely normal to the coastline. We simulate the coastal-marine solute spreading for these two types of cases over a 5-year period (2005-2009) under different solute load scenarios. Results show essentially similar concentration spreading into the sea for similar (diffuse or large-river) loading from land in the parallel (1) as the normal (2) coastline flow-transport case. For nutrients, loading from land is much greater (smaller) and, as such, has much greater (smaller) reach in total (per-capita) terms from coast (2). These results have fairness implications for the per-capita load reductions required in The Baltic Sea Action Plan, which are on average smaller for the larger Swedish per-capita loads.

Implication of grain-size trend analysis in sediment transport pathways determination (Southeastern Baltic Sea)

Aira Dubikaltienė, Institute of Geosciences, aira.dub@gmail.com (presenter)

Donatas Pupienis, Nature Research Center; Dovilė Karlonienė, Institute of Geosciences; Kristina Viršilaitė, Institute of Geosciences; Darius Jarmalavičius, Nature Research Center; Gintautas Žilinskas, Nature Research Center

The aim of this study was to determine the sediments transport pathways in the Southeastern Baltic Sea by applying grain-size trend analysis. In total 844 surface bottom sediment samples were used. The sediment transport vectors have a general direction from shallow water towards the depression. The sediment transport trends are in relatively good agreement with the previous published results.

The assessment of sediment transport in oceans and seas are problematic because of limited access and possibility for in situ measurements to carry out. Therefore, sediment transport investigation is often based on alternative methods, such as grain size statistical parameters analysis and interpretation. Our aim was to determine the sediments transport pathways in the Southeastern Baltic Sea using grain-size trend analysis method. This study is based on grain size analysis of 844 surface bottom sediment samples. The Klaipėda-Ventspils and Curonian-Sambian plateaus are covered by fine-coarse sands, while in northern part of Gdansk depression the silt predominates. The preliminary results show that sand sediments are transported in northwest and north direction, whereas silt sediment vectors are directed to west or southwest. The calculated sediment transport vectors have a general direction from shallow water and plateaus towards the Gdansk depression. The obtained sediment transport pathways are in relatively good agreement with the previous in situ measurements and modeling results.

The South-Western Baltic coast storm surge event Axel in a climate perspective

Nikolaus Groll, Helmholtz-Zentrum Geesthacht, Centre for Material and Coastal Research, nikolaus.groll@hzg.de (presenter)

Ute Deawel, Helmholtz-Zentrum Geesthacht, Centre for Material and Coastal Research; Beate Geyer, Helmholtz-Zentrum Geesthacht, Centre for Material and Coastal Research

To assess marine climate variability and long-term changes in the Baltic Sea, long homogenous data set are important. Using new marine hindcasts with 3d physical-biogeochemical model ECOSMO and the ocean wave model WAM using the new regional reanalysis COMSO REA6 as atmospheric forcing, will provide such climate data. Results from the hindcast will be discussed and compared to observations.

To assess climate variability and long-term changes in marine environments, homogenous data sets over long time periods are important. Even in the North and Baltic Sea with a relatively good spatial observational coverage, datasets with a long enough temporal coverage to analyse climate variability are rare. In recent decades numerical hindcast simulations of complex marine systems became a common tool to overcome the lack of the spatial and temporal coverage with observations.

However, challenges related to model simulations include, besides model errors and inaccuracies, the identification of uncertainties due to the forcing conditions and the model setup. Within the project MarEns we aim to asses the latter uncertainties, by using an ensemble of atmospheric forcing data and model setups. As one of the atmospheric forcing the regional atmospheric reanalysis COSMO REA6 from the German Weather Service is used to drive the 3d physical-biogeochemical model ECOSMO and the ocean wave model WAM.

The results from the hindcasts will be discussed with focus on the Baltic Sea and compared to observations and other available hindcast simulations using alternative forcing data.

Particle shuttling and oxidation efficiency of sedimentary organic carbon in contrasting brackish marine environments

Madeleine Nilsson, University of Gothenburg, SMHI; N. Ekeroth, University of Gothenburg; M. Kononets, University of Gothenburg; A. Hylén, University of Gothenburg; L. Viktorsson, SMHI, E. Almroth Rosell, SMHI, P. Roos, Technical University of Denmark, A. Tengberg, University of Gothenburg; P.O.J. Hall, University of Gothenburg, per.hall@marine.gu.se (presenter)

Indications of considerable focusing of particulate organic carbon (POC) by large-scale particle shuttling along depth gradients in the Baltic Sea were revealed from analyses of an extensive data set of benthic OC oxidation efficiencies (oxidation rate in relation to OC inventory in surficial sediment). The investigated data set contain in situ lander measurements of benthic dissolved inorganic carbon (DIC) fluxes, OC burial rates as well as sediment accumulation rates in different depositional regimes (i.e. accumulation and erosion/transport bottoms) in the Baltic Sea. With the exception of permanently oxic stations, we found a positive correlation between the DIC efflux and the normalized water depth (water depth/maximum water depth in the basin) in the Baltic Proper and Gulf of Finland. The DIC flux was not correlated with OC inventories in the upper reactive layer of the sediment. Instead, the efficiency of OC oxidation increased with increasing normalized water depth. The reason for this pattern was largely explained by the age of the uppermost sediment layer (0–2 cm), which was found to be youngest at the deep accumulation bottoms. This finding was further supported by the high content of fresh labile organic material (as indicated by chlorophyll-a) at these sites, and is most likely explained by particle shuttling, i.e. resuspension and redistribution of POC from shallow to deeper bottoms. A very high POC oxidation efficiency was also characteristic for permanently oxygenated sites in the Baltic Proper, probably due to stimulation of organic matter degradation by bioturbation. Despite similar inventories of OC in the sediment, OC oxidation rates were significantly lower in the oligotrophic Gulf of Bothnia than in the Baltic Proper and the Gulf of Finland. The lower oxidation efficiency of deposited POC in the Gulf of Bothnia, compared to the other basins, is most likely a result of terrestrial matter making up a larger proportion of the sedimentary POC-pool in this basin as indicated by elevated sedimentary organic C/N ratios.

Enhanced sedimentary phosphorus release following a natural oxygenation event

Astrid Hylén, University of Gothenburg; Sebastiaan van de Velde, University of California; Mingyue Luo, Vrije Universiteit Brussel; Mikhail Kononets, University of Gothenburg; Elin Almroth Rosell, SMHI; Per O.J. Hall, University of Gothenburg, per.hall@marine.gu.se (presenter)

The Baltic Sea contains one of the largest hypoxic zones in the world as a consequence of severe eutrophication. The eutrophication and hypoxia are sustained largely by elevated phosphate fluxes from hypoxic sediments. In 2015, parts of these long-term hypoxic sediments were oxygenated by a deep-water inflow from the North Sea. During four yearly expeditions in 2015-2018, we studied whether the oxygenation event would lead to a long-term removal of dissolved inorganic phosphate (DIP) from the water column through burial in the sediment. Measurements of pore water DIP and solid phase phosphorus fractions showed that 4.8 – 8.4 mmol P m-2 were retained in the sediment by adsorption onto iron oxides right after the inflow, but that less than half of this fraction remained when the system returned to anoxia. Sediment-water fluxes of DIP and other biogenic compounds were measured in situ using a benthic chamber lander. Intriguingly, the efflux of these compounds increased considerably after the inflow before stepwise decreasing to pre-inflow values. This increase in fluxes was likely caused by temporarily elevated organic matter remineralisation rates due to the oxygenation event. As a result, the net sedimentary DIP release increased with about 70-100 % per m2 over the measurement period compared to a scenario without the inflow. In conclusion, the transient oxygenation caused by the inflow had minor effects on long-term sedimentary phosphorus retention. Furthermore, this small retention was completely offset by the enhanced DIP release from degradation of organic matter. The inflow thus worsened the eutrophication situation in the Baltic Sea.

Effects of endobenthic meiofauna on sediment profiles (O2, H2S & pH) and bacterial community structure

Johanna Hedberg, Stockholm University, johannahedberg84@gmail.com (presenter)

Francisco Nascimento, Stockholm University; Sven Iburg, Stockholm University; Ugo Marzoccho, Aarhus University; Stefano Bonaglia, Stockholm University

Meiofauna was successfully extracted from hypoxic coastal Baltic Sea sediments and a gradient of abundance was created in the lab. Both oxygen penetration depths and sulphide appearance fronts in the cores were affected by the meiofauna and the microbial community structure was significantly different among treatments, suggesting an effect of meiofauna on sediment chemistry and biology.

Baltic Sea sediments are sites of intense nutrient (re)cycling due to high nutrient input from catchment, high degradation rates and the occurring state of oxygen depleted areas. An increasing number of studies has been quantifying nutrient fluxes from Baltic sediments. However, the role of endobenthic meiofauna on sediment biogeochemistry is much less understood. The aim of this study was to investigate how different abundances of meiofauna affected sulphide, oxygen and pH dynamics, together with bacterial community structure in highly impacted hypoxic Baltic Sea sediments. Meiofauna was successfully extracted from the sediment alive and added to otherwise intact cores to create a gradient of abundance. Microsensor profiling were conducted three times at 1-week intervals during the course of the experiment and showed that higher abundance of meiofauna affected the oxygen penetration depths and sulphide appearance fronts at the end of the experiment. The microbial community structure showed a significant difference among treatments, suggesting an effect of meiofauna on sediment chemistry and biology.

Acoustic and geochemical survey of the MET1 site – an active pockmark field located in the central Gulf of Gdańsk (Southern Baltic)

Jakub Idczak, University of Gdańsk, j.idczak@ug.edu.pl (presenter)

Damian Jaśniewicz, Polish Academy of Sciences; Aleksandra Brodecka-Goluch, University of Gdańsk; Zygmunt Klusek, Polish Academy of Sciences; Natalia Gorska, University of Gdańsk; Patryk Pezacki, University of Gdańsk; Jerzy Bolałek, University of Gdańsk

An active pockmark field with irregular nature of gas-bearing sediments has been found in the central part of the Gulf of Gdańsk. It has been investigated over a 10-year period. Profiles of methane concentration in sediments turned out to be significantly different outside and inside the main pockmark. The magnitude of gas emission decreased over time.

The MET1 site (~80 m water depth) has been continuously investigated since 2009 in terms of methane presence. Different acoustic devices have been used: sub-bottom profiler, side-scan sonar, multi-, split- and single-beam as well as, chirp echosounders. Additionally, core sampling was performed in 2009, 2014, 2017 and 2018 in different parts of the study area and several pockmarks (total square area: 311000 m2) have been discovered. Profiles of methane concentration in sediments turned out to be significantly different outside and inside the main pockmark. The obtained data revealed irregular nature of the gas-bearing sediments inside the pockmark, with significant discontinuity zones and general development of the main pockmark over time. Permanent gas emission has been observed within the main structure, however, its magnitude decreased over a 10-year period. Hydroacoustic study carried out in the water column showed the abundance of fish within the pockmark field in relation to the neighboring areas, while the underwater ROV inspection revealed the presence of microbial mats at the bottom. This study was financed by the Polish National Science Centre (UMO-2016/21/B/ST10/02369).

Lithological and geochemical anomalies on the Baltic Sea coast (Curonian Spit, Lithuania)

Dovile Karloniene, Vilnius University, dovile.karloniene@chgf.vu.lt (presenter)

Donatas Pupienis, Vilnius University; Gintautas Žilinskas, Nature Research Centre; Darius Jarmalavičius, Nature Research Centre; Aira Dubikaltienė, Vilnius University; Kristina Viršilaitė, Vilnius University

Lithological and geochemical anomalies in the Curonian Spit sea coast indicated on sites with prevailing coarse sand and highest heavy metal concentrations determined in the very coarse (>1.00 mm), fine and very fine (<0.16 mm) sediment fractions. It is most likely that the heavy metals are of natural origin because of the presence of the heavy minerals in the coarser sediments.

Heavy metals (HM) are among the most common pollutants, especially in the Baltic Sea region. Magnetic susceptibility (MS) method can be valuable when targeting and selecting sampling sites for HM analyses. In this study, we analysed the beach sediments from the Curonian Spit – natural and anthropogenically undisturbed area. MS values of beach sediments measured in situ with a Bartington MS3 field scanning sensor and sand grain size assessed in the laboratory. HMs were partially extracted in acid solution and measured with ICP-MS. Results showed that MS values and the size of the sediment particles, tend to decrease from south to north, i.e., towards the spit formation direction. The HMs content slight positively correlated with MS values and sediment particles sizes. The HM anomalies determined on sites with prevailing coarse sand. The geochemical analysis of different sand fractions of the coarse sand sample revealed that the highest HM concentrations were in the very coarse (>1.00 mm), fine and very fine (<0.16 mm) sediment fractions. It is most likely that the HMs anomalies are of natural origin because of the presence of the heavy minerals in the coarser sediments.

Increasing densities of an invasive polychaete enhance bioturbation with variable effects on solute fluxes

Laura Kauppi, University of Helsinki, laura.kauppi@helsinki.fi (presenter)

Guillaume Bernard, CNRS/University of Bordeaux; Ralf Bastrop, University of Rostock; Alf Norkko, University of Helsinki; Joanna Norkko, University of Helsinki

Increasing densities of the polychaete Marenzelleria spp. enhance bioturbation but effects on solute fluxes vary depending on the solute, species density and identity, and the composition of the surrounding community. This implies spatial and temporal differences in their effects on ecosystem functioning.

The invasive polychaete genus Marenzelleria spp. has increased species and functional diversity in the Baltic Sea with possible density-dependent effects on bioturbation and associated solute fluxes. We tested the effects of increasing density of the different Marenzelleria species on bioturbation and solute fluxes in a laboratory experiment. In general, the polychaetes enhanced all bioturbation metrics, but the effects on solute fluxes varied depending on the solute, on the density and species identity of Marenzelleria, and on the species and functional composition of the surrounding community. M. viridis and M. neglecta were more important in predicting variation in phosphate and silicate fluxes, whereas M. arctia had a larger effect on nitrogen cycling. The complex direct and indirect pathways indicate the importance of considering the whole community and not just species in isolation in the experimental studies. The results also imply spatial and temporal differences in the effects of Marenzelleria spp. on ecosystem functioning.

The influence of the Major Baltic Inflows on the sub-halocline pH variability

Silvie Lainela, Tallinn University of Technology, silvie.lainela@taltech.ee (presenter)

Major Baltic Inflows (MBIs) have significant impact on the biogeochemistry of the Baltic Sea. Biogeochemical processes together with organic matter mineralization influence the alteration of pH in marine environment. The Baltic Proper sub-halocline pH data together with ancillary information have been evaluated in the context of the MBI events.

Major Baltic Inflows (MBIs) have significant impact on the physical conditions and biogeochemistry of the Baltic Sea. During the past decades only a few major MBI events have occurred, latest in December 2014. The latter caused highest salinities of the previous 40-60 years, but fresh oxygen did not reach further from the Gotland Deep.

Biogeochemical processes together with organic matter mineralization influence the alteration of pH. In the central Baltic Proper a permanent halocline separates the less saline cold layer from the warmer more saline deep water. Eutrophication increases the mineralization of organic matter in deep layer and causes a decrease in oxygen and pH. During anoxic mineralization formation of sulphide ions and release of ammonia generates large amount of alkalinity, stabilizing pH around 7. These processes are reversed during deep layer renewal events.

The Baltic Proper sub-halocline pH data together with ancillary information have been evaluated in the context of the MBI events. For more detailed evaluation of the spatial variability the comparison of three different pH methodologies were used to take account the specificities of the Baltic Sea.

Synoptic scale assessment of oxygen depletion in the Gulf of Finland

Taavi Liblik, Department of Marine Systems at Tallinn University of Technology, taavi.liblik@taltech.ee (presenter)

Stella-Theresa Stoicescu, Department of Marine Systems at Tallinn University of Technology; Jaan Laanemets, Department of Marine Systems at Tallinn University of Technology; Oliver Samlas, Department of Marine Systems at Tallinn University of Technology; Ivan Kuprijanov, Department of Marine Systems at Tallinn University of Technology; Fred Buschmann, Department of Marine Systems at Tallinn University of Technology; Urmas Lips, Department of Marine Systems at Tallinn University of Technology

We combine and present data from ship surveys and moored vertical profiling to estimate sub-surface oxygen conditions in the Gulf of Finland. This allows us to compile oxygen distribution maps with weekly temporal resolution. We will present spatial statistics of sub-surface oxygen conditions, the role of physical processes in shaping the conditions and the impact on benthic communities.

Sub-surface oxygen conditions in the Gulf of Finland are strongly impacted by physical processes. Major Baltic Inflows rather deteriorate oxygen conditions in the gulf. Unlike the Central Baltic, wind forcing has strong impact on the area occupied by hypoxic water in the time scales from a few days to seasons. This has been shown by spatial mappings along the gulf and data from the fixed moorings. However, areal extent of hypoxic bottoms in the whole Baltic Sea is today typically presented as seasonal maps, which are often based on very limited data in the gulf.

Oxygen distributions estimated by spatial ship surveys and by data of fixed vertical profiling in the central gulf show in most cases very good coincidence. This allows us to fill the gaps between ship surveys by vertical profiling measurements and compile oxygen distribution maps with weekly temporal resolution. Statistical maps of oxygen situation will be presented and the role of physical processes influencing the areal extent of hypoxia in the gulf will be explained. Likewise, the impact of hypoxic area variability on benthic communities will be discussed.

Winter re-stratification events and their consequences in the NE Baltic Sea

Taavi Liblik, Department of Marine Systems at Tallinn University of Technology, taavi.liblik@taltech.ee (presenter)

Germo Väli, Department of Marine Systems at Tallinn University of Technology; Kai Künnis-Beres, Department of Marine Systems at Tallinn University of Technology; Madis-Jaak Lilover, Department of Marine Systems at Tallinn University of Technology; Inga Lips, Department of Marine Systems at Tallinn University of Technology; Jaan Laanemets, Department of Marine Systems at Tallinn University of Technology

We analyse CTD data collected in the NE Baltic during winter months in the last decade. We show the observational evidences of temporary re-stratification events, which elevated chl a fluorescence in the upper layer. Spatial extent and duration of the events is analysed by data of in-situ measurements and output of numerical model. The impact to the phytoplankton will be discussed.

Stratification has strong seasonality in the Baltic Sea. Seasonal thermocline vanishes due to convection and wind stirring in every winter. Temperature values drop below the temperature of maximum density in the upper layer in the NE Baltic Sea. General understanding is that the water column is mixed down to the halocline during winter.

In the present study, we analyse CTD data collected in the NE Baltic during winter months in the last decade. We show the observational evidences of re-stratification events. These events were caused by the advection of fresher water in the surface layer during the periods when the estuarine circulation was prevailing in the study area. Upper mixed layer depth during these events was well shallower than the euphotic depth and elevated values of chl a fluorescence were observed despite very low temperature. Temporal and spatial extent of these fresher and cold water events in the surface layer were also analysed using simulation data from GETM (General Estuarine Transport Model). The impact of these events to the phytoplankton biomass and species composition will be discussed.

Cyanobacteria blooms in in the Baltic Sea: A review on models and facts

Britta Munkes, Geomar, bmunkes@geomar.de (presenter)

Ulrike Loeptien, Geomar & Institute of Geosciences, University of Kiel; Heiner Dietze, Geomar & Institute of Geosciences, University of Kiel

This review summarizes our current understanding on cyanobacteria in the Baltic Sea. We compare the specific model formulations of five different coupled biogeochemical ocean models (BALTSEM, CEMBS, ECOSMO, ERGOM and SCOBI) and put these into perspective with direct observations and laboratory studies from literature.

The Baltic Sea has, despite intensive management efforts, still severe eutrophication problems. Nitrogen-fixing cyanobacteria are linked to the eutrophication problem of the Baltic, as they can fuel the primary productivity by adding additional nitrogen to the already overfertilized system. This review summarizes our current understanding on cyanobacteria in the Baltic Sea. We compare the specific model formulations of five state-of-the-art coupled biogeochemical ocean models (BALTSEM, CEMBS, ECOSMO, ERGOM and SCOBI), that were designed for political decision making. Examples for the considered processes are differences in grazing formulations, temperature dependence of growth and half-saturation constants. The model assumptions are then compared to direct observations and laboratory studies from the literature. Specifically, we highlight large differences between species and non-model-resolved processes.

Vertical profiles of hydrophobic organic contaminants (HOCs) in the sediment-water interface – assessing the impact of organic carbon cycling on HOC fate in the marine environment

Inna Nybom, Stockholm University / ACESo, inna.nybom@aces.su.se (presenter)

Anna Sobek, Stockholm University / ACESo

To study the effects of organic carbon origin on the sediment-water fluxes of hydrophobic organic contaminants (HOCs) sediment porewater-bottom water interface was sampled. Results until now have shown strong concentration gradient for several HOCs, indicating a potential flux from sediment to water. Further data will give insights into effects of the different organic carbon cycling on HOC fate.

Environmental fate of hydrophobic organic contaminants (HOCs) is closely linked to cycling of organic carbon (OC). In this project, we hypothesize that OC origin (i.e. terrestrial versus marine) and thus its sorption capacity, affects sediment-water fluxes of HOCs. Four sites with in the Baltic Sea and a Norwegian Fjord, with different primary production regimes and relative contributions of terrestrial versus marine OC, were sampled. Equilibrium passive samplers mounted on a sediment-water interface probe were used to sample freely dissolved HOCs. The OC origin at the different sites was determined using stable carbon isotope signatures (δ13C). Data from the Norwegian site (representing low input of terrestrial organic matter) exhibited a high resolution profile of the sediment porewater-bottom water interface for a wide range of HOCs (PCBs, PAHs, pesticides and chlorobenzenes). A strong concentration gradient between sediment pore water and overlying bottom water was observed for several PAHs indicating a potential flux of the chemicals from sediment to water. Further data will provide insights into effects of the different OC cycling on HOC fate at the investigated sites.

Dissolved oxygen variability (2013-2018) in the Southern Baltic Sea and its impact on the Baltic cod

Daniel Rak, The Institute of Oceanology of the Polish Academy of Sciences (IO PAN), rak@iopan.gda.pl (presenter)

Waldemar Walczowski, The Institute of Oceanology of the Polish Academy of Sciences (IO PAN); Lidia Dzierzbicka-Głowacka, The Institute of Oceanology of the Polish Academy of Sciences (IO PAN); Sergey Shchuka, Shirshov Institute of Oceanology; Anna Przyborska, The Institute of Oceanology of the Polish Academy of Sciences (IO PAN)

This poster presents the dissolved oxygen variability in the Southern Baltic Sea. The presented results of DO changes involve the time variability as well as the changes of DO under influence of the inflows. The cod’s spermatozoa activation together with neutral egg buoyancy layers for the Bornholm Basin and Słupsk Furrow have been presented.

This poster presents the dissolved oxygen (DO) concentration changes in the Southern Baltic Sea. Combination of data obtained during the r/v Oceania cruises (2013-2017), from the moored system (2018) and Argo floats (2018) allowed us to estimate the oxygenation of a whole water column. The monthly mean dissolved oxygen concentrations, as well as detailed yearly surface layers DO cycle has been presented. Moreover, the DO decline time after the major Baltic inflows (MBI) in 2014 was estimated at about 3.5 years for the Bornholm Deep and Słupsk Furrow. While the Bornholm Basin was relatively well oxygenated, the low oxygen concentration

Do we need a new definition for MBI if we can do with the old one?

Oleg Savchuk, Stockholm University Baltic Sea Center, oleg.savchuk@su.se (presenter)

Recently invented indices for ""MBI"" might be useful for characterization of the salt transport. But, as such they can even be misleading for indication of ventilation of Baltic Sea deeps

The answer depends on underlying concept and intended usage of the term “Major Baltic Inflow” rather than on a method of its determination (estimation). Apparently, these sporadic MBIs have from the very beginning (e.g. Fonselius, Dickson) been identified and traced by their capability to supply the deep layers with oxygen brought with salty (=heavy) waters propagated along the bottom from the Entrance area. Thus, the most important property of every such event is as how deep and far it would reach into the Central Baltic, i.e. what water volumes and bottom areas would be refreshed. That, in turn is determined by specific “intensity” of inflow expressed, e.g. with the Q96 index, which successfully singles out inflows reaching deep into the Baltic Sea, e.g. arriving to the Gotland Deep. From such perspective, the estimates of salt transport per se, however important they are for the Baltic Sea salt budget, are less useful for characterization of ventilation. Therefore, the calculation and publication of Q96 time-series should be continued. These considerations are illustrated and discussed with performances of different indices both in the Bornholm and Gotland deeps.

Accounting for dissolved organic nutrients reduces uncertainty in forcing

Oksana Vladimirova, Russian State Hydrometeorological University, 3256767@gmail.com

Tatyana Eremina, Russian State Hydrometeorological University; Alexey Isaev, P.P. Shirshov Institute of Oceanology; Vladimir Ryabchenko, P.P. Shirshov Institute of Oceanology; Oleg Savchuk, Stockholm University Baltic Sea Center (presenter)

Three-dimensional modelling of dissolved organic nutrients.

As demonstrated by the recent compilation of multiple-model simulations of the Baltic Sea eutrophication, one of the major uncertainties in historical and scenario simulations is generated by considerable differences in the prescribed nutrient loads. These differences originate from the models’ formulations and calibration, including assumptions on bioavailable fractions in external nutrient inputs. In result, the external loads range between models up to 50 % for nitrogen and almost three-fold for phosphorus. To eliminate this kind of uncertainties, St.-Petersburg model of eutrophication (SPBEM) has been modified by explicit description of total amounts of organic nutrients, including both dissolved and particulate forms. Namely, besides N and P detritus variables, the dynamics of labile and refractory fractions of dissolved organic nitrogen and phosphorus are now described with four additional equations. The modification was developed and calibrated in numerical experiments at the Gulf of Finland made with plausible initial and realistic boundary conditions for the recent years. Results of both model-data comparison and sensitivity analysis are presented and discussed.