The human-induced increases in atmospheric carbon dioxide since the beginning of the industrial revolution have led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. To date, surface ocean acidity has increased by 30% compared with pre-industrial times. The aim of this study was to investigate the relationship between increasing pCO2, decreasing pH and changes in volatile dimethylsulphide (DMS) and halocarbon concentrations, through 70,000 litre, high pCO2 mesocosm experiments and laboratory culture studies. DMS is a climatically important trace gas produced by marine algae: it transfers sulphur into the atmosphere and is a major influence on biogeochemical climate feedbacks. Halocarbons are also important biogenic trace gases which undergo atmospheric photochemical degradation, releasing halide radicals to participate in atmospheric ozone cycling, and transfer halogens from sea to land. Evidence is presented from a Norwegian coastal study which showed a 60% DMS, 30% DMSP and 40% iodocarbon reduction in high pCO2 mesocosms, and in the Baltic Sea, known for its low-salinity, cyanobacterial dominated community, where DMS concentrations showed an 80% reduction under high pCO2 but halocarbon concentrations were unaffected. No decrease in DMS or DMSP concentrations were identified in high pCO2 laboratory cultures of the DMSproducing species Emiliania huxleyi RCC1229, and halocarbons were undetectable. Changes in trace gas concentrations may arise due to pH effects on the interactions between microbial producers and consumers. Other effects may arise from cell biochemistry due to long-term adaptation to increased ρCO2 and reduced pH on the enzymatic activity production of the compounds. Further studies should determine the nature of the pCO2 and pH effect on bacterial interactions with DMS, DMSP and halocarbon production and breakdown. There should also be attention given to the DMS source in the cyanobacterial-dominated community of the Baltic Sea.
Posts Tagged 'Baltic'
The effects of elevated CO2 and ocean acidification on the production of marine biogenic trace gases
Published 18 August 2015 Science ClosedTags: Baltic, biogeochemistry, biological response, BRcommunity, field, laboratory, mesocosms, North Atlantic, prokaryotes
Seagrass beds as ocean acidification refuges for mussels? High resolution measurements of pCO2 and O2 in a Zostera marina and Mytilus edulis mosaic habitat
Published 23 July 2015 Science ClosedTags: algae, Baltic, biogeochemistry, BRcommunity, chemistry, field, mollusks, primary production, respiration
It has been speculated that macrophytes beds might act as a refuge for calcifiers from ocean acidification. In the shallow nearshores of the western Kiel Bay (Baltic Sea), mussel and seagrass beds are interlacing, forming a mosaic habitat. Naturally, the diverse physiological activities of seagrasses and mussels are affected by seawater carbonate chemistry and they locally modify it in return. Calcification by shellfishes is sensitive to seawater acidity; therefore the photosynthetic activity of seagrasses in confined shallow waters creates favorable chemical conditions to calcification at daytime but turn the habitat less favorable or even corrosive to shells at night. In contrast, mussel respiration releases CO2, turning the environment more favorable for photosynthesis by adjacent seagrasses. At the end of summer, these dynamics are altered by the invasion of high pCO2/low O2 coming from the deep water of the Bay. However, it is in summer that mussel spats settle on the leaves of seagrasses until migrating to the permanent habitat where they will grow adult. These early life phases (larvae/spats) are considered as most sensitive with regard to seawater acidity. So far, the dynamics of CO2 have never been continuously measured during this key period of the year, mostly due to the technological limitations. In this project we used a combination of state-of-the-art technologies and discrete sampling to obtain high-resolution time-series of pCO2 and O2 at the interface between a seagrass and a mussel patch in Kiel Bay in August and September 2013. From these, we derive the entire carbonate chemistry using statistical models. We found the monthly average pCO2 more than 50 % (approx. 640 μatm for August and September) above atmospheric equilibrium right above the mussel patch together with large diel variations of pCO2 within 24 h: 887 ± 331 μatm in August and 742 ± 281 μatm in September (mean ± SD). We observed important daily corrosiveness for calcium carbonates (Ωarag and Ωcalc < 1) centered on sunrise. On the positive side, the investigated habitat never suffered from hypoxia during the study period. We emphasize the need for more experiments on the impact of these acidic conditions on (juvenile) mussels with a focus on the distinct day-night variations observed. Continue reading ‘Seagrass beds as ocean acidification refuges for mussels? High resolution measurements of pCO2 and O2 in a Zostera marina and Mytilus edulis mosaic habitat’
Impact of seawater carbonate chemistry on the calcification of marine bivalves (update)
Published 21 July 2015 Science ClosedTags: Baltic, biological response, calcification, laboratory, mollusks, morphology, physiology, respiration
Bivalve calcification, particularly of the early larval stages, is highly sensitive to the change in ocean carbonate chemistry resulting from atmospheric CO2 uptake. Earlier studies suggested that declining seawater [CO32−] and thereby lowered carbonate saturation affect shell production. However, disturbances of physiological processes such as acid-base regulation by adverse seawater pCO2 and pH can affect calcification in a secondary fashion. In order to determine the exact carbonate system component by which growth and calcification are affected it is necessary to utilize more complex carbonate chemistry manipulations. As single factors, pCO2 had no effects and [HCO3–] and pH had only limited effects on shell growth, while lowered [CO32−] strongly impacted calcification. Dissolved inorganic carbon (CT) limiting conditions led to strong reductions in calcification, despite high [CO32−], indicating that [HCO3–] rather than [CO32−] is the inorganic carbon source utilized for calcification by mytilid mussels. However, as the ratio [HCO3–] / [H+] is linearly correlated with [CO32−] it is not possible to differentiate between these under natural seawater conditions. An equivalent of about 80 μmol kg−1 [CO32−] is required to saturate inorganic carbon supply for calcification in bivalves. Below this threshold biomineralization rates rapidly decline. A comparison of literature data available for larvae and juvenile mussels and oysters originating from habitats differing substantially with respect to prevailing carbonate chemistry conditions revealed similar response curves. This suggests that the mechanisms which determine sensitivity of calcification in this group are highly conserved. The higher sensitivity of larval calcification seems to primarily result from the much higher relative calcification rates in early life stages. In order to reveal and understand the mechanisms that limit or facilitate adaptation to future ocean acidification, it is necessary to better understand the physiological processes and their underlying genetics that govern inorganic carbon assimilation for calcification.
Direct effects of increased CO2 concentrations in seawater on the net primary production of charophytes in a shallow, coastal, brackish-water ecosystem
Published 8 July 2015 Science ClosedTags: algae, Baltic, biological response, chemistry, field, mesocosms, photosynthesis, primary production
Charophytes are found in fresh and brackish waters across the globe and play key roles in coastal ecosystems. However, their response to increasing CO2 is not well understood. The aim of the study was to detect the effects of elevated CO2 on the physiology of charophyte species growing in the brackish Baltic Sea by measuring net primary production. Mesocosm experiments were conducted in the Kõiguste Bay (N Gulf of Riga) during the field season of 2012. Separate mesocosms were maintained at different pCO2 levels: ~2000, ~1000 and ~200 µatm. The experiments were carried out with three species of charophytes: Chara aspera, C. tomentosa and C. horrida. The short-term photosynthetic responses of charophytes to different treatments were measured by the oxygen method. The results show that elevated CO2 levels in brackish water may enhance the photosynthetic activity of charophyte species and suggest that increasing CO<sub>2</sub> in the Baltic Sea could have implications for interspecific competition and community structure in a future high CO2 world.
Warming, but not enhanced CO2 concentration, quantitatively and qualitatively affects phytoplankton biomass
Published 11 June 2015 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, growth, laboratory, mesocosms, multiple factors, otherprocess, phytoplankton, primary production, temperature
We investigated the impacts of predicted ocean acidification and future warming on the quantity and nutritional quality of a natural phytoplankton autumn bloom in a mesocosm experiment. Since the effects of CO2-enrichment and temperature have usually been studied independently, we were also interested in the interactive effects of both aspects of climate change. Therefore, we used a factorial design with 2 temperature and 2 acidification levels in a mesocosm experiment with a Baltic Sea phytoplankton community. Our results show a significant time-dependent influence of warming on phytoplankton carbon, chlorophyll a, and particulate organic carbon. Phytoplankton carbon, for instance, decreased by more than half with increasing temperature at bloom time. Additionally, elemental carbon to phosphorus ratios (C:P) increased significantly, by approximately 5 to 8%, due to warming. Impacts of CO2 or synergetic effects of warming and acidification could not be detected. We suggest that stronger grazing pressure induced by temperature was responsible for the significant decline in phytoplankton biomass. Our results suggest that the biological effects of warming on Baltic Sea phytoplankton are considerable and will likely have fundamental consequences for trophic transfer in the pelagic food web.
Warming and ocean acidification effects on phytoplankton—from species shifts to size shifts within species in a mesocosm experiment
Published 4 June 2015 Science ClosedTags: abundance, Baltic, biological response, community composition, mesocosms, morphology, multiple factors, otherprocess, phytoplankton, temperature
While the isolated responses of marine phytoplankton to climate warming and to ocean acidification have been studied intensively, studies on the combined effect of both aspects of Global Change are still scarce. Therefore, we performed a mesocosm experiment with a factorial combination of temperature (9 and 15°C) and pCO2 (means: 439 ppm and 1040 ppm) with a natural autumn plankton community from the western Baltic Sea. Temporal trajectories of total biomass and of the biomass of the most important higher taxa followed similar patterns in all treatments. When averaging over the entire time course, phytoplankton biomass decreased with warming and increased with CO2 under warm conditions. The contribution of the two dominant higher phytoplankton taxa (diatoms and cryptophytes) and of the 4 most important species (3 diatoms, 1 cryptophyte) did not respond to the experimental treatments. Taxonomic composition of phytoplankton showed only responses at the level of subdominant and rare species. Phytoplankton cell sizes increased with CO2 addition and decreased with warming. Both effects were stronger for larger species. Warming effects were stronger than CO2 effects and tended to counteract each other. Phytoplankton communities without calcifying species and exposed to short-term variation of CO2 seem to be rather resistant to ocean acidification.
Growth and survival in a changing environment: Combined effects of moderate hypoxia and low pH on juvenile bivalve Macoma balthica
Published 12 May 2015 Science ClosedTags: Baltic, biological response, growth, laboratory, mollusks, mortality, multiple factors, oxygen
Baltic Sea species live in a complex, variable environment characterized by highly fluctuating hydrology, including large seasonal and diel pH variations. For decades, oxygen deficiency caused by anthropogenic eutrophication has affected the Baltic Sea, and large areas of the seafloor are permanently hypoxic resulting in severely degraded benthic communities. Species living in this system are thus potentially tolerant and adapted to this fluctuating environment, but also vulnerable as illustrated by high mortality of benthic species as a result of hypoxia. In future, the frequency and extent of regularly co-occurring low oxygen and low pH levels will likely increase with on-going climate change. A key species in the Baltic Sea soft-bottom communities, the bivalve Macoma balthica (L.), experiences such conditions throughout its life-cycle, and therefore serves as a good model organism for studying the combined effects of oxygen and pH conditions. To study the response of M. balthica to multiple changes occurring in the benthic environment, we conducted an experiment to investigate the survival and shell growth of newly settled juveniles simultaneously exposed to two pH levels (7.85 and 7.35) and two oxygen levels (8.5 and 3.0 mg/l) for 29 days in a fully factorial design. Survival was high in all treatments (> 60%), but significantly higher in the two low oxygen treatments (> 70%). Although positive growth was observed in all treatments, pH and oxygen as well as their interaction significantly affected relative growth. The highest growth was observed in the “low O2/high pH” treatment, which was 2.4 times higher than in both treatments with high oxygen. Although the mechanism for these differences remains unknown, hypoxia-induced metabolic depression likely plays a role. Our results highlight the need to know more about the occurrence and performance of benthic species regularly exposed to changing conditions, and of the range and conditions encountered in situ. With the predicted future negative changes in oxygen availability as well as pH, the adaptive responses of benthic species to multiple stressors will be critical in understanding ecosystem dynamics in the face of change.
Effect of elevated CO2 on organic matter pools and fluxes in a summer, post spring-bloom Baltic Sea plankton community
Published 12 May 2015 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, field, mesocosms, otherprocess, phytoplankton
Ocean acidification is expected to influence plankton community structure and biogeochemical element cycles. To date, experiments with nutrient stimulated blooms have been primarily used to study the response of plankton communities to elevated CO2. In this CO2 manipulation study, we used large-volume (~55 m3) pelagic in situ mesocosms to enclose a natural, post spring-bloom plankton assemblage in the Baltic Sea to investigate the response of organic matter pools to ocean acidification. In the mesocosms, fCO2 was manipulated yielding a range of average fCO2 of 365 to ~1231 μatm with no adjustment of naturally available nutrient concentrations. Plankton community development and key biogeochemical element pools were subsequently followed in this nitrogen-limited ecosystem over a period of seven weeks.
We identified three distinct phases based on temperature fluctuations and plankton biomass: a warm, productive period with elevated chlorophyll a and particulate matter concentrations (Phase I), a decline in autotrophic biomass coinciding with cooler water temperatures associated with lower incoming photosynthetically active radiation (PAR) and higher zooplankton grazing pressure (Phase II), and a steady state phase with low net change in particulate and dissolved matter pools (Phase III). We observed higher sustained chlorophyll a and particulate matter concentrations (~25% higher) and lower inorganic phosphate concentrations in the water column in the highest fCO2 treatment (1231 μatm) in Phase III. Size-fractionated phytoplankton pigment analyses indicated that these differences were driven by picophytoplankton (< 2 μm) and were already established early in the experiment during Phase I. However the influence of picophytoplankton on bulk organic matter pools was masked by high biomass of larger plankton until Phase III when the small size fraction (< 2 μm) contributed up to 90% of chlorophyll a. Furthermore, CO2-related differences in water column suspended matter concentrations were not reflected in sinking material flux. Our results from this study indicate that ocean acidification could have significant and sustained impacts on pelagic biogeochemical element pools in nitrogen-limited ecosystems.
Modeling the role of pH on Baltic Sea cyanobacteria
Published 7 April 2015 Science ClosedTags: abundance, Baltic, biological response, growth, individualmodeling, modeling, otherprocess, prokaryotes, regionalmodeling
We simulate pH-dependent growth of cyanobacteria with an ecosystem model for the central Baltic Sea. Four model components—a life cycle model of cyanobacteria, a biogeochemical model, a carbonate chemistry model and a water column model—are coupled via the framework for aquatic biogeochemical models. The coupled model is forced by the output of a regional climate model, based on the A1B emission scenario. With this coupled model, we perform simulations for the period 1968–2098. Our simulation experiments suggest that in the future, cyanobacteria growth is hardly affected by the projected pH decrease. However, in the simulation phase prior to 1980, cyanobacteria growth and N2-fixation are limited by the relatively high pH. The observed absence of cyanobacteria before the 1960s may thus be explained not only by lower eutrophication levels, but also by a higher alkalinity.
Continue reading ‘Modeling the role of pH on Baltic Sea cyanobacteria’
Impact of seawater carbonate chemistry on the calcification of marine bivalves
Published 4 February 2015 Science ClosedTags: Baltic, biological response, calcification, laboratory, mollusks, morphology, physiology, respiration
Bivalve calcification, particular of the early larval stages is highly sensitive to the change of ocean carbonate chemistry resulting from atmospheric CO2 uptake. Earlier studies suggested that declining seawater [CO32−] and thereby lowered carbonate saturation affect shell production. However, disturbances of physiological processes such as acid-base regulation by adverse seawater pCO2 and pH can affect calcification in a secondary fashion. In order to determine the exact carbonate system component by which growth and calcification are affected it is necessary to utilize more complex carbonate chemistry manipulations. As single factors, pCO2 had no and [HCO3−] and pH only limited effects on shell growth, while lowered [CO32−] strongly impacted calcification. Dissolved inorganic carbon (CT) limiting conditions led to strong reductions in calcification, despite high [CO32−], indicating that [HCO3−] rather than [CO32−] is the inorganic carbon source utilized for calcification by mytilid mussels. However, as the ratio [HCO3−] / [H+] is linearly correlated with [CO32−] it is not possible to differentiate between these under natural seawater conditions. Therefore, the availability of [HCO3−] combined with favorable environmental pH determines calcification rate and an equivalent of about 80 μmol kg−1 [CO32−] is required to saturate inorganic carbon supply for calcification in bivalves. Below this threshold biomineralization rates rapidly decline. A comparison of literature data available for larvae and juvenile mussels and oysters originating from habitats differing substantially with respect to prevailing carbonate chemistry conditions revealed similar response curves. This suggests that the mechanisms which determine sensitivity of calcification in this group are highly conserved. The higher sensitivity of larval calcification seems to primarily result from the much higher relative calcification rates in early life stages. In order to reveal and understand the mechanisms that limit or facilitate adaptation to future ocean acidification, it is necessary to better understand the physiological processes and their underlying genetics that govern inorganic carbon assimilation for calcification.
Continue reading ‘Impact of seawater carbonate chemistry on the calcification of marine bivalves’
Metabolic rate and activity of blue mussel Mytilus edulis trossulus under short-term exposure to carbon dioxide-induced water acidification and oxygen deficiency
Published 23 December 2014 Science ClosedTags: Baltic, biological response, laboratory, mollusks, multiple factors, oxygen, physiology
This work investigated the effect of carbon dioxide-induced decreased water pH (8.1 – control, 7.5 and 7.0), oxygen saturation (~100% and ~20%) and the combination of both factors on the behaviour (gaping activity) and the total metabolic rate of blue mussel Mytilus edulis trossulus from the southern Baltic Sea. Heat dissipation measurements were carried out in a Calvet-type isothermal twin calorimeter equipped with a flow-through system. The resting metabolic rate was not significantly (p > 0.05) affected by pH or oxygen saturation. Neither was there significant (p > 0.05) effect of the interaction of both factors on this process. The high inter-individual variability in behaviour affected the value of maximal recorded activity and duration of activity peaks connected with shell gaping behaviour. In some mussels, they were short and appeared periodically, and other individuals were inactive or exhibited temporal activity terms of different duration. The lowered oxygen saturation significantly (p < 0.05) affected the time spent on activity. However, there was no effect (p > 0.05) of lowered pH on this parameter, which indicates that oxygen deficiency may affect the Baltic population of M. edulis trossulus more seriously than acidification.
Juvenile sea stars exposed to acidification decrease feeding and growth with no acclimation potential
Published 8 September 2014 Science ClosedTags: adaptation, Baltic, biological response, calcification, echinoderms, growth, laboratory, mortality, otherprocess, performance, physiology
Ocean acidification has the potential to affect growth and calcification of benthic marine invertebrates, particularly during their early life history. We exposed field-collected juveniles of Asterias rubens from Kiel Fjord (western Baltic Sea) to 3 seawater CO2 partial pressure (pCO2) levels (ranging from around 650 to 3500 µatm) in a long-term (39 wk) and a short-term (6 wk) experiment. In both experiments, survival and calcification were not affected by elevated pCO2. However, feeding rates decreased strongly with increasing pCO2, while aerobic metabolism and NH4+ excretion were not significantly affected by CO2 exposure. Consequently, high pCO2 reduced the scope for growth in A. rubens. Growth rates decreased substantially with increasing pCO2 and were reduced even at pCO2 levels occurring in the habitat today (e.g. during upwelling events). Sea stars were not able to acclimate to higher pCO2, and growth performance did not recover during the long-term experiment. Therefore, the top-down control exerted by this keystone species may be diminished during periods of high environmental pCO2 that already occur occasionally and will be even higher in the future. However, some individuals were able to grow at high rates even at high pCO2, indicating potential for rapid adaption. The selection of adapted specimens of A. rubens in this seasonally acidified habitat may lead to higher CO2 tolerance in adult sea stars of this population compared to the juvenile stage. Future studies need to address the synergistic effects of multiple stressors such as acidification, warming and reduced salinity, which will simultaneously impact the performance of sea stars in this habitat.
Health and population-dependent effects of ocean acidification on the marine isopod Idotea balthica
Published 26 August 2014 Science ClosedTags: Baltic, biological response, crustaceans, laboratory, mortality, physiology
Three populations of the grazing isopod Idotea balthica were exposed to high CO2 treatment for a period of 20 days to investigate the effect of ocean acidification (OA) on animal health and immunocompetence. The results of the populations from more saline habitats were comparable and showed a 60–80 % decrease in immune response as a result of the high CO2 treatment. Analysis of protein carbonyls showed no treatment effect, indicating that short-term OA does not increase oxidative protein damage. Meanwhile, the third tested population from the lower saline Baltic Sea had higher background protein carbonyl levels. Ocean acidification in addition to this resulted in 100 % mortality. The results of this study show that OA reduced immunocompetence of this marine isopod. In addition, populations and individuals in poor health are potentially at greater risk to succumb under OA.
Effect on pCO2 by phytoplankton uptake of dissolved organic nutrients in the Central and Northern Baltic Sea, a model study
Published 21 August 2014 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, chemistry, growth, modeling, mortality, otherprocess, phytoplankton, primary production, regionalmodeling
Dissolved organic matter (DOM) has been added to an existing biogeochemical model and the phytoplankton were allowed to utilize the dissolved organic nutrients for primary production. The results show typical vertical structures for dissolved organic carbon (DOC), and improved or maintained model skill for both mean vertical profiles and mean seasonal variation of biogeochemical variables, evaluated by objective skill metrics. Due to scarce DOM measurements in the Baltic Sea it was hard to validate the new variables, but the model can recreate the general magnitude and distribution of terrestrial and in situ produced DOC, DON, and DOP, as far as we know them. The improvements are especially clear for the total nutrient levels and in recreating the biological drawdown of CO2 in the Eastern Gotland basin. Without phytoplankton uptake of dissolved organic nitrogen and phosphate, CO2 assimilation is lower during the summer months and the partial pressure of CO2 increases by about 200 μatm in the Eastern Gotland Basin, while in the Bothnian Bay, both the duration and magnitude of CO2 assimilation are halved. Thus the phytoplankton uptake of dissolved organic nutrients lowers pCO2 in both basins. Variations in the river transported DOM concentration mainly affect the magnitude of the summer cyanobacteria bloom.
Multiple stressors threatening the future of the Baltic Sea–Kattegat marine ecosystem: implications for policy and management actions
Published 23 July 2014 Science ClosedTags: Baltic, multiple factors, policy, review, temperature
The paper discusses the combined effects of ocean acidification, eutrophication and climate change on the Baltic Sea and the implications for current management strategies. The scientific basis is built on results gathered in the BONUS+ projects Baltic-C and ECOSUPPORT. Model results indicate that the Baltic Sea is likely to be warmer, more hypoxic and more acidic in the future. At present management strategies are not taking into account temporal trends and potential ecosystem change due to warming and/or acidification, and therefore fulfilling the obligations specified within the Marine Strategy Framework Directive, OSPAR and HELCOM conventions and national environmental objectives may become significantly more difficult. The paper aims to provide a basis for a discussion on the effectiveness of current policy instruments and possible strategies for setting practical environmental objectives in a changing climate and with multiple stressors.
Coping with climate change? Copepods experience drastic variations in their physicochemical environment on a diurnal basis
Published 21 July 2014 Science ClosedTags: abundance, Baltic, biological response, crustaceans, field, laboratory, multiple factors, otherprocess, performance, temperature, zooplankton
Migratory zooplankton, such as copepods experience widely varying conditions in their physicochemical environment on a diurnal basis. The amplitude of the fluctuations may affect the copepods’ ability to respond to climate change. The environment in coastal areas is naturally fluctuating and the effects of ocean acidification are difficult to predict. Negative effects on copepods may affect the whole food web as they are the most abundant zooplankton, constituting a major part of the diet of fish. In this study, we determined the vertical profiles of an array of environmental variables and the vertical distribution of common copepods in a shallow coastal area of the Baltic Sea. We sampled once a month, in June, July and August, every sixth hour during 24 h. We found that copepods experience a change in pH of more than 0.5 units and 5 °C change in temperature during migration. Thus, on diurnal time scales copepods experience a range in their physicochemical environment that is equal to or larger than the predicted climate change scenarios.
Precision and accuracy of spectrophotometric pH measurements at environmental conditions in the Baltic Sea
Published 27 May 2014 Science ClosedTags: Baltic, chemistry, field, methods
The increasing uptake of anthropogenic CO2 by the oceans has raised an interest in precise and accurate pH measurement in order to assess the impact on the marine CO2-system. Spectrophotometric pH measurements were refined during the last decade yielding a precision and accuracy that cannot be achieved with the conventional potentiometric method. However, until now the method was only tested in oceanic systems with a relative stable and high salinity and a small pH range. This paper describes the first application of such a pH measurement system at conditions in the Baltic Sea which is characterized by a wide salinity and pH range. The performance of the spectrophotometric system at pH values as low as 7.0 (“total” scale) and salinities between 0 and 35 was examined using TRIS-buffer solutions, certified reference materials, and tests of consistency with measurements of other parameters of the marine CO2 system. Using m-cresol purple as indicator dye and a spectrophotometric measurement system designed at Scripps Institution of Oceanography (B. Carter, A. Dickson), a precision better than ±0.001 and an accuracy between ±0.01 and ±0.02 was achieved within the observed pH and salinity ranges in the Baltic Sea. The influence of the indicator dye on the pH of the sample was determined theoretically and is presented as a pH correction term for the different alkalinity regimes in the Baltic Sea. Because of the encouraging tests, the ease of operation and the fact that the measurements refer to the internationally accepted “total” pH scale, it is recommended to use the spectrophotometric method also for pH monitoring and trend detection in the Baltic Sea.
The marine carbonate system: ionic interactions and biogeochemical processes
Published 19 May 2014 Science ClosedTags: Arctic, Baltic, biogeochemistry, chemistry, modeling, regionalmodeling
The absorption of atmospheric carbon dioxide (CO2) by seawater and subsequent equilibrium reactions within this ionic medium give rise to a complex chemical system often referred to as the marine carbonate system. This system is influenced by physical and biogeochemical processes in the ocean. The marine carbonate system is a major component of the global carbon cycle and is, by virtue of its interaction with atmospheric CO2, of fundamental importance to the Earth’s climate. Accurate knowledge of the properties of the marine carbonate system is a prerequisite for understanding the chemical forcing and consequences of key biogeochemical processes such as biological production, organic matter respiration, or uptake of anthropogenic carbon. The assessment of the marine carbonate system builds on precise measurements by state-of-the-art analytical methods as well as an understanding of the underlying fundamental chemistry in terms of ionic interactions and equilibrium thermodynamics. This thesis focuses on different aspects of the marine carbonate system with emphasis on biogeochemical processes and thermodynamic modelling of the seawater ionic medium. A quantitative understanding of the equilibrium solution chemistry of seawater ultimately relies on accurate estimations of activity coefficients of all the various components that make up the solution. Activity coefficients of the carbonate system in sodium chloride solution of varying ionic strength were estimated by Monte Carlo simulations at different temperatures, as well as activity coefficients of chloride and sulfate salts of a simplified seawater electrolyte, suggesting that a complete Monte Carlo description of seawater activity coefficients may be achievable using the hard sphere approach with a very limited number of fitted parameters. Chemical speciation modelling showed that the measured excess alkalinity of Baltic seawater is consistent with an organic alkalinity derived from humic substances of terrestrial origin. In deep waters of the Baltic Sea, oxygen and sulfate was found to be the major electron acceptors to the remineralization of organic matter under different redox conditions. It was further suggested that this organic matter predominantly had a terrestrial origin. The subsurface waters of the central Arctic Ocean were found to be a sink of anthropogenic CO2, attributed to uptake by source waters of Atlantic origin. The seaice covered central Arctic Ocean was also shown to harbor low, but significant biological productivity. Late summer net community production was estimated using multiple approaches based on both discrete and underway measurements and results showed large spatial variability between the deep basins with extremes at the marginal ice zone.
Continue reading ‘The marine carbonate system: ionic interactions and biogeochemical processes’
Responses of filamentous cyanobacteria to natural and anthropogenic changes in the Baltic Sea
Published 3 March 2014 Science ClosedTags: Baltic, biogeochemistry, biological response, BRcommunity, community composition, field, growth, laboratory, multiple factors, nitrogen fixation, nutrients, otherprocess, photosynthesis, phytoplankton, primary production, prokaryotes
The studies concentrated on 2 diazotrophic cyanobacteria species, Nodularia spumigena and Aphanizomenon sp.. The dissertation includes diurnal observations, laboratory and field studies. The experiments aimed to observe variations concerning day/night rhythms and anthropogenic induced changes of pCO2 levels. I showed 2 to 4 fold diurnal variations within DIC, N2, DIP incorporations, related to daytime and bloom development. Further I showed stimulated C and N2 fixation rates with increasing pCO2 at sufficient DIP concentrations. Reduced or depleted DIP concentrations debate this effect.
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The influence of dissolved organic matter on the acid–base system of the Baltic Sea
Published 12 February 2014 Science ClosedTags: Baltic, biogeochemistry, chemistry
To assess the influence of dissolved organic matter (DOM) on the acid–base system of the Baltic Sea, 19 stations along the salinity gradient from Mecklenburg Bight to the Bothnian Bay were sampled in November 2011 for total alkalinity (AT), total inorganic carbon concentration (CT), partial pressure of CO2 (pCO2), and pH. Based on these data, an organic alkalinity contribution (Aorg) was determined, defined as the difference between measured AT and the inorganic alkalinity calculated from CT and pH and/or CT and pCO2. Aorg was in the range of 22–58 μmol kg– 1, corresponding to 1.5–3.5% of AT. The method to determine Aorg was validated in an experiment performed on DOM-enriched river water samples collected from the mouths of the Vistula and Oder Rivers in May 2012. The Aorg increase determined in that experiment correlated directly with the increased DOC concentration caused by enrichment of the > 1 kDa DOM fraction. To examine the effect of Aorg on calculations of the marine CO2 system, the pCO2 and pH values measured in Baltic Sea water were compared with calculated values that were based on the measured alkalinity and another variable of the CO2 system, but ignored the existence of Aorg. Large differences between measured and calculated pCO2 and pH were obtained when the computations were based on AT and CT. The calculated pCO2 was 27–56% lower than the measured value whereas the calculated pH was overestimated by more than 0.4 pH units. Since biogeochemical models are based on the transport and transformations of AT and CT, the acid–base properties of DOM should be included in calculations of the CO2 system in DOM-rich basins like the Baltic Sea. In view of our limited knowledge about the composition and acid/base properties of DOM, this is best achieved using a bulk dissociation constant, KDOM, that represents all weakly acidic functional groups present in DOM. Our preliminary results indicated that the bulk KDOM in the Baltic Sea is 2.94 · 10– 8 mol kg– 1. Although this KDOM has no thermodynamic meaning, it can be a useful tool in numerical studies as it allows an approximation of Aorg in seawater.
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