Determination of gaseous elemental mercury air-sea exchange in the Baltic Sea

2020 ◽  
Author(s):  
Stefan Osterwalder ◽  
Michelle Nerentorp ◽  
Wei Zhu ◽  
Erik Nilsson ◽  
Mats Nilsson ◽  
...  
Keyword(s):  
Wind Speed ◽  
Baltic Sea ◽  
Elemental Mercury ◽  
The Baltic Sea ◽  
Transfer Velocity ◽  
Field Station ◽  
Gaseous Elemental Mercury ◽  
Starting Point ◽  
Flux Measurements ◽  
The Baltic

<p>Ocean waters store approximately 400 Gg of mercury (Hg) and exchange it with the atmosphere at a high rate. Air-sea exchange of gaseous elemental mercury (Hg<sup>0</sup>) is a key process in global Hg cycling because evasion lowers the reservoir of Hg(II) available for methylation and subsequent bioaccumulation in marine fish and prolongs the atmospheric lifetime and subsequently global cycling of Hg. However, global estimates on the air-sea flux are not well constrained (1.9 to 4.2 Gg a<sup>-1</sup>) mainly because high-resolution measurements of Hg<sup>0</sup> in seawater are largely lacking and parameterization of the Hg<sup>0</sup> transfer velocity introduces uncertainties in Hg<sup>0</sup> flux modelling. We present estimates of the net Hg<sup>0</sup> flux for the Baltic Sea derived from land-based marine measurements of Hg<sup>0</sup> in air and seawater as well as micrometeorological techniques. We found that coastal waters at the ICOS field station Östergarnsholm, located east of Gotland, Sweden, were typically supersaturated with seawater Hg<sup>0</sup> (mean ± SD = 13.5 ± 3.5 ng m<sup>-3</sup>; ca. 10 % of total Hg) compared to ambient Hg<sup>0</sup> (1.3 ± 0.2 ng m<sup>-3</sup>). The Hg<sup>0</sup> flux calculated using gas-transfer wind speed relationships ranged from 0.1 to 1.3 ng m<sup>-2</sup> h<sup>-1</sup> over the course of the campaign (May 10 – June 20, 2017). The modeled Hg<sup>0</sup> flux showed a distinct diel pattern with an average daytime flux of 0.6 ng m<sup>-2</sup> h<sup>-1</sup> and nighttime flux of 0.4 ng m<sup>-2</sup> h<sup>-1</sup>, indicating that temperature and light induced production of seawater Hg<sup>0</sup> was of significance in shallow waters. Preliminary calculations of the average coastal Hg<sup>0</sup> flux simultaneously measured using direct, non-intrusive gradient-based, aerodynamic gradient and relaxed eddy accumulation techniques were 0.5 ± 1, 0.6 ± 3.8 and 0.6 ± 37 ng m<sup>-2</sup> h<sup>-1</sup>, respectively. Although, these flux estimates were in good agreement, there were indications in the temporal patters of the observations, which suggest that there is a need to reconsider the modeled flux with the support of more direct flux measurements. Direct flux measurements revealed not only Hg<sup>0</sup> evasion but also periods of Hg<sup>0</sup> dry deposition. In addition, direct measurements indicated a stronger wind speed dependence of the Hg<sup>0</sup> transfer velocity compared to CO<sub>2</sub> which appears to coincide with whitecap formation in the open sea flux footprint (wind speed > 5 m s<sup>-1</sup>). Hence, we anticipate this study as a starting point for more land-based, marine, continuous measurements of seawater Hg<sup>0</sup> concentration in combination with micrometeorological fluxes in order to improve Hg<sup>0</sup> flux estimates in regional and global scale models. In this context, directly measured Hg<sup>0</sup> fluxes will be pivotal to improve transfer velocity estimates of Hg<sup>0</sup> especially during periods of high wind speed.</p>

scholarly journals Variability of air-sea gas transfer velocities in the Baltic Sea

2018 ◽  
Author(s):  
Leila Nagel ◽  
Kerstin E. Krall ◽  
Bernd Jähne
Keyword(s):  
Heat Transfer ◽  
Wind Speed ◽  
Baltic Sea ◽  
Active Material ◽  
Gas Transfer ◽  
The Baltic Sea ◽  
Transfer Velocity ◽  
Wind Speeds ◽  
The Baltic ◽  
Surface Active Material

Abstract. Heat transfer velocities measured during three different campaigns in the Baltic Sea using the Active Controlled Flux Technique (ACFT) with wind speeds ranging from 5.3 to 14.8 m s−1 are presented. Careful scaling of the heat transfer velocities to gas transfer velocities using Schmidt number exponents measured in a laboratory study allows to compare the measured transfer velocities to existing gas transfer velocity parameterizations, which use wind speed as the controlling parameter. The measured data and other field data clearly show that some gas transfer velocities are much lower than the empirical wind speed parametrizations. This indicates that the dependencies of the transfer velocity on the fetch, i.e., the history of the wind and the age of the wind wave field, and the effects of surface active material need to be taken into account.

scholarly journals Measurements of air–sea gas transfer velocities in the Baltic Sea

Ocean Science ◽  
2019 ◽  
Vol 15 (2) ◽  
pp. 235-247 ◽  
Author(s):  
Leila Nagel ◽  
Kerstin E. Krall ◽  
Bernd Jähne
Keyword(s):  
Heat Transfer ◽  
Wind Speed ◽  
Baltic Sea ◽  
Active Material ◽  
Gas Transfer ◽  
The Baltic Sea ◽  
Transfer Velocity ◽  
Wind Speeds ◽  
The Baltic ◽  
Surface Active Material

Abstract. Heat transfer velocities measured during three different campaigns in the Baltic Sea using the active controlled flux technique (ACFT) with wind speeds ranging from 5.3 to 14.8 m s−1 are presented. Careful scaling of the heat transfer velocities to gas transfer velocities using Schmidt number exponents measured in a laboratory study allows us to compare the measured transfer velocities to existing gas transfer velocity parameterizations, which use wind speed as the controlling parameter. The measured data and other field data clearly show that some gas transfer velocities are much lower than those based on the empirical wind speed parameterizations. This indicates that the dependencies of the transfer velocity on the fetch, i. e., the history of the wind and the age of the wind-wave field, and the effects of surface-active material need to be taken into account.

scholarly journals Assessment of Wind Shear and Wind Energy Potential in the Baltic Sea Region of Latvia

2015 ◽  
Vol 52 (2) ◽  
pp. 26-39
Author(s):  
V. Bezrukovs ◽  
Vl. Bezrukovs ◽  
A. Zacepins ◽  
V. Komashilovs
Keyword(s):  
Wind Speed ◽  
Wind Energy ◽  
Baltic Sea ◽  
Density Fluctuations ◽  
Western Coast ◽  
The Baltic Sea ◽  
Energy Potential ◽  
North East ◽  
Wind Energy Potential ◽  
The Baltic

Abstract The paper is devoted to the investigation into the wind energy potential based on long-term observations of the wind speed and energy density fluctuations at heights from 10 to 160 m on the Baltic Sea coast of Latvia. During the observations (2004 - 2013), the wind speed and direction values were measured, and the statistical database was accumulated using a LOGGER 9200 Symphonie measuring systems mounted on 60 m masts - one on the western coast and another on the north-east of Latvia. From June 2011 to May 2012, these measurements were complemented with the data for the heights from 40 to 160 m obtained by means of a ZephIR lidar and with the metrological data provided by “Latvian Environment, Geology and Meteorology Centre” for the same period. The graphs of seasonal fluctuations in the wind speed were obtained for the heights up to 160 m by measurements over the period of 2007 - 2013. The results of the research on the wind speed distribution up to 200 m are promising for evaluation of the wind energy potential of Latvia and will be helpful in assessment of prospective sites for construction of WPPs.

Addressing the effects of bottom trawling on benthic processes using experimental and field studies in the Baltic Sea

2020 ◽  
Author(s):  
Claudia Morys ◽  
Martin Jakobsson ◽  
Mattias Sköld ◽  
Pere Masqué ◽  
Volker Brüchert ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Field Experiments ◽  
Biogeochemical Cycling ◽  
Field Studies ◽  
The Baltic Sea ◽  
Bottom Trawling ◽  
Flux Measurements ◽  
The Baltic ◽  
Benthic Ecosystems ◽  
The Impact

<p>Bottom trawling is one of the most important anthropogenic disturbances affecting marine ecosystems and there has been increased attention to its impacts on seabed habitats as well as the structure and functioning of benthic ecosystems. The impact of bottom trawling is well-known with regard to benthic organisms. However, we still have a poor understanding of its effects on bentho-pelagic coupling and biogeochemical cycling in the sediment. In the Baltic Sea, the study area of the present investigation, there is a particular lack of data.<br>Here, we present new results from field experiments to quantify changes in sediment properties, macrofauna and biogeochemical cycling after the passage of a benthic dredge. To put the results in a broader context, a field survey was conducted in six areas of different commercial trawling intensities in the Bornholm Basin. Acoustic geophysical mapping, isotope profiling, functional categorization of macrofauna and sediment-water nutrient and oxygen flux measurements were used to evaluate the physical disturbance of the seabed. Preliminary results suggest a range of ecological, biogeochemical and physical impacts of trawling in the Baltic Sea, with implications for benthic ecosystem functioning.</p>

scholarly journals Sensitivity of the air–sea CO<sub>2</sub> exchange in the Baltic Sea and Danish inner waters to atmospheric short term variability

2014 ◽  
Vol 11 (12) ◽  
pp. 16993-17042
Author(s):  
A. S. Lansø ◽  
J. Bendtsen ◽  
J. H. Christensen ◽  
L. L. Sørensen ◽  
H. Chen ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Co2 Flux ◽  
Co2 Concentration ◽  
Co2 Exchange ◽  
Atmospheric Co2 ◽  
The Baltic Sea ◽  
Short Term ◽  
Transfer Velocity ◽  
The Baltic ◽  
Short Term Variability

Abstract. Minimising the uncertainties in estimates of air–sea CO2 exchange is an important step toward increasing the confidence in assessments of the CO2 cycle. Using an atmospheric transport model makes it possible to investigate the direct impact of atmospheric parameters on the air–sea CO2 flux along with its sensitivity to e.g. short-term temporal variability in wind speed, atmospheric mixing height and the atmospheric CO2 concentration. With this study the importance of high spatiotemporal resolution of atmospheric parameters for the air–sea CO2 flux is assessed for six sub-basins within the Baltic Sea and Danish inner waters. A new climatology of surface water partial pressure of CO2 (pCO2) has been developed for this coastal area based on available data from monitoring stations and underway pCO2 measuring systems. Parameterisations depending on wind speed were applied for the transfer velocity to calculate the air–sea CO2 flux. Two model simulations were conducted – one including short term variability in atmospheric CO2 (VAT), and one where it was not included (CAT). A seasonal cycle in the air–sea CO2 flux was found for both simulations for all sub-basins with uptake of CO2 in summer and release of CO2 to the atmosphere in winter. During the simulated period 2005–2010 the average annual net uptake of atmospheric CO2 for the Baltic Sea, Danish Straits and Kattegat was 287 and 471 Gg C yr-1 for the VAT and CAT simulations, respectively. The obtained difference of 184 Gg C yr-1 was found to be significant, and thus ignoring short term variability in atmospheric CO2 does have a sizeable effect on the air–sea CO2 exchange. The combination of the atmospheric model and the new pCO2 fields has also made it possible to make an estimate of the marine part of the Danish CO2 budget for the first time. A net annual uptake of 2613 Gg C yr-1 was found for the Danish waters. A large uncertainty is connected to the air–sea CO2 flux in particular caused by the transfer velocity parameterisation and the applied pCO2 climatology. However, the present study underlines the importance of including short term variability in the atmospheric CO2 concentration in future model studies of the air–sea exchange in order to minimise the uncertainty.

scholarly journals Potential links between Baltic Sea submarine terraces and groundwater seeping

2020 ◽  
Vol 8 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Martin Jakobsson ◽  
Matt O'Regan ◽  
Carl-Magnus Mörth ◽  
Christian Stranne ◽  
Elizabeth Weidner ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Geological Mapping ◽  
The Baltic Sea ◽  
Remotely Operated Vehicle ◽  
Sea Floor ◽  
Groundwater Levels ◽  
Starting Point ◽  
Glacial Clay ◽  
Stockholm Archipelago ◽  
The Baltic

Abstract. Submarine groundwater discharge (SGD) influences ocean chemistry, circulation, and the spreading of nutrients and pollutants; it also shapes sea floor morphology. In the Baltic Sea, SGD was linked to the development of terraces and semicircular depressions mapped in an area of the southern Stockholm archipelago, Sweden, in the 1990s. We mapped additional parts of the Stockholm archipelago, areas in Blekinge, southern Sweden, and southern Finland using high-resolution multibeam sonars and sub-bottom profilers to investigate if the sea floor morphological features discovered in the 1990s are widespread and to further address the hypothesis linking their formation to SGD. Sediment coring and sea floor photography conducted with a remotely operated vehicle (ROV) and divers add additional information to the geophysical mapping results. We find that terraces, with general bathymetric expressions of about 1 m and lateral extents of sometimes >100 m, are widespread in the surveyed areas of the Baltic Sea and are consistently formed in glacial clay. Semicircular depressions, however, are only found in a limited part of a surveyed area east of the island of Askö, southern Stockholm archipelago. While submarine terraces can be produced by several processes, we interpret our results to be in support of the basic hypothesis of terrace formation initially proposed in the 1990s; i.e. groundwater flows through siltier, more permeable layers in glacial clay to discharge at the sea floor, leading to the formation of a sharp terrace when the clay layers above seepage zones are undermined enough to collapse. By linking the terraces to a specific geologic setting, our study further refines the formation hypothesis and thereby forms the foundation for a future assessment of SGD in the Baltic Sea that may use marine geological mapping as a starting point. We propose that SGD through the submarine sea floor terraces is plausible and could be intermittent and linked to periods of higher groundwater levels, implying that to quantify the contribution of freshwater to the Baltic Sea through this potential mechanism, more complex hydrogeological studies are required.

scholarly journals High-resolution measurements of elemental mercury in surface water for an improved quantitative understanding of the Baltic Sea as a source of atmospheric mercury

2017 ◽  
Author(s):  
Joachim Kuss ◽  
Siegfried Krüger ◽  
Johann Ruickoldt ◽  
Klaus-Peter Wlost
Keyword(s):  
Surface Water ◽  
High Resolution ◽  
Baltic Sea ◽  
Elemental Mercury ◽  
Ambient Air ◽  
Atmospheric Mercury ◽  
Small Scale ◽  
The Baltic Sea ◽  
Marginal Seas ◽  
The Baltic

Abstract. Marginal seas are directly subjected to anthropogenic and natural influences from land in addition to receiving inputs from the atmosphere and open ocean. Together these lead to pronounced gradients and strong dynamic changes. However, in the case of mercury emissions from these seas, estimates often fail to adequately account for the spatial and temporal variability of the elemental mercury concentration in surface water (Hg0wat). In this study, a method to measure Hg0wat at high resolution was devised and subsequently validated. The better-resolved Hg0wat dataset, consisting of about one measurement per nautical mile, yielded insight into the sea's small-scale variability and thus improved the quantification of the sea's Hg0 emissions, a major source of atmospheric mercury. Research campaigns in the Baltic Sea were carried out between 2011 and 2015 during which Hg0 both in surface water and in ambient air were measured. For the former, two types of equilibrators were used. A membrane equilibrator enabled continuous equilibration and a bottle equilibrator assured that equilibrium was reached for validation. The measurements were combined with data obtained in the Baltic Sea in 2006 from a bottle equilibrator only. The Hg0 sea-air flux was newly calculated with the combined dataset based on current knowledge of the Hg0 Schmidt number, Henry's law constant, and a widely used gas-exchange transfer velocity parameterization. By using a newly developed pump-CTD with increased pumping capability in the Hg0 equilibrator measurements, Hg0wat could also be characterized in deeper water layers. A process study carried out near the Swedish island Øland in August 2015 showed that the upwelling of Hg0-depleted water contributed to Hg0 emissions of the Baltic Sea. However, a delay of a few days after contact between the upwelled water and light was apparently necessary before the biotic and abiotic transformations of ionic to volatile Hg0 produced a distinct sea-air Hg0 concentration gradient. This study clearly showed spatial, seasonal, and interannual variability in the Hg0 sea-air flux of the Baltic Sea. The average annual Hg0 emission was 0.90 ± 0.18 Mg for the Baltic Proper and to 1.73 ± 0.32 Mg for the entire Baltic Sea, which is about half the amount entrained by atmospheric deposition. A comparison of our results with the Hg0 sea-air fluxes determined in the Mediterranean Sea and in marginal seas in East Asia were to some extent similar but they partly differed in terms of the deviations in the amount and seasonality of the flux.

Diet composition of herring (Clupea harengus L.) and cod (Gadus morhua L.) in the southern Baltic Sea in 2007 and 2008

2011 ◽  
Vol 40 (4) ◽  
Author(s):  
Diana Dziaduch
Keyword(s):  
Baltic Sea ◽  
Diet Composition ◽  
Gadus Morhua ◽  
Clupea Harengus ◽  
The Baltic Sea ◽  
Commercial Fish ◽  
Southern Baltic Sea ◽  
Starting Point ◽  
Southern Baltic ◽  
The Baltic

AbstractDiet composition of two commercial fish species, herring and cod, were studied in some regions (mainly Gda’nsk and Bornholm Basins, and the Polish coast) of the southern Baltic Sea in 2007 and 2008. Herring is the dominant zooplanktivorous species in the ecosystem of the Baltic Sea, but apart from mesoplanktonic organisms it also eats macroplanktonic and benthic species in considerable amount. The diet of cod consists of fish and crustaceans from pelagic, hyperbenthic and benthic habitats. The feeding preferences of fish indirectly reflect changes in the whole food chain in the Baltic Sea. This research focuses specifically on these invertebrate species, which are eliminated from the environment by most of the ichthyofauna of this region. The aim of this research is to examine the role of invertebrate organisms belonging to Crustacea in the diet of herring and adult cod to supply updated results about feeding of these fish as little data have been collected since the 1990s. The present study is a preliminary survey and results can not be considered conclusive. The restricted numbers of analyzed stomachs of fish and selected seasons of the year addressed in this paper are a starting point for further studies with a larger scope. In this study, 20 to 90% of herring had empty stomachs. Mesozooplankton dominated the diets of small and large herring. Mysidacea, which were historically important prey for herring, are now scarce and have been replaced by planktonic Amphipoda. In the case of cod, consumption of Mysidacea has never been as low as in this study. As for other invertebrate prey, the benthic isopod Saduria and Crangon shrimp achieved the highest amount by number and weight. These results show distinct changes in diet when compared to previous investigations and require verification at a larger spatial scale.

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