Sea-Air Exchange of Methane in Shallow Inshore Areas of the Baltic Sea

We report sea-air fluxes of methane in physically and biologically distinct inshore habitats of the Baltic Sea with the goal to establish empirical relationships that allow upscaling of local site-specific flux measurements. Flux measurements were conducted using floating chambers with and without bubble shields, and by using a boundary layer gas transfer model before, during, and after an annually occurring algal bloom from June to October 2019. Water and air temperature, salinity, wind, sediment organic content, and organic content of floating algal biomass were found to successfully discriminate the different habitats in terms of methane flux, both over periods of days and over a season. Multivariate statistical analysis was used to establish the relative environmental forcing of methane emissions over one growth season for each flux method. Floating algal biomass carbon and sediment organic content were identified as the most important controlling factors for methane emissions based on flux chamber measurements over a period of days to weeks, whereas water and air temperature and wind velocity were the most important factors based on the gas transfer model on these time scales. Over the season, water and air temperature were the most important controlling factors with both methods. We present a first attempt how our observations can be extrapolated to determine the coastal methane emission along the coastline.

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

10.5194/egusphere-egu2020-22362 ◽

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

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. 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.

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Interactive comment to “Variability of air-sea gas transfer velocity on the Baltic Sea” by Nagel et al.

10.5194/os-2018-108-rc2 ◽

2018 ◽

Author(s):

Anonymous

Keyword(s):

Baltic Sea ◽

Gas Transfer ◽

The Baltic Sea ◽

Transfer Velocity ◽

Gas Transfer Velocity ◽

The Baltic

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Numerical modelling of thermodynamics and dynamics of sea ice in the Baltic Sea

Ocean Science ◽

10.5194/os-7-257-2011 ◽

2011 ◽

Vol 7 (2) ◽

pp. 257-276 ◽

Cited By ~ 9

Author(s):

A. Herman ◽

J. Jedrasik ◽

M. Kowalewski

Keyword(s):

Sea Ice ◽

Baltic Sea ◽

Air Temperature ◽

Ice Cover ◽

Surface Fluxes ◽

Rate Of Change ◽

The Baltic Sea ◽

Ice Dynamics ◽

Ice Concentration ◽

The Baltic

Abstract. In this paper, a numerical dynamic-thermo-dynamic sea-ice model for the Baltic Sea is used to analyze the variability of ice conditions in three winter seasons. The modelling results are validated with station (water temperature) and satellite data (ice concentration) as well as by qualitative comparisons with the Swedish Meteorological and Hydrological Institute ice charts. Analysis of the results addresses two major questions. One concerns effects of meteorological forcing on the spatio-temporal distribution of ice concentration in the Baltic. Patterns of correlations between air temperature, wind speed, and ice-covered area are demonstrated to be different in larger, more open sub-basins (e.g., the Bothnian Sea) than in the smaller ones (e.g., the Bothnian Bay). Whereas the correlations with the air temperature are positive in both cases, the influence of wind is pronounced only in large basins, leading to increase/decrease of areas with small/large ice concentrations, respectively. The other question concerns the role of ice dynamics in the evolution of the ice cover. By means of simulations with the dynamic model turned on and off, the ice dynamics is shown to play a crucial role in interactions between the ice and the upper layers of the water column, especially during periods with highly varying wind speeds and directions. In particular, due to the fragmentation of the ice cover and the modified surface fluxes, the ice dynamics influences the rate of change of the total ice volume, in some cases by as much as 1 km3 per day. As opposed to most other numerical studies on the sea-ice in the Baltic Sea, this work concentrates on the short-term variability of the ice cover and its response to the synoptic-scale forcing.

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

10.5194/os-2018-108 ◽

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.

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CO2-flux measurements above the Baltic Sea at two heights: flux gradients in the surface layer?

Earth System Science Data ◽

10.5194/essd-7-311-2015 ◽

2015 ◽

Vol 7 (2) ◽

pp. 311-317 ◽

Cited By ~ 2

Author(s):

A. Lammert ◽

F. Ament

Keyword(s):

Baltic Sea ◽

Eddy Covariance ◽

Latent Heat ◽

Co2 Flux ◽

The Baltic Sea ◽

Near Surface ◽

Constant Flux ◽

Flux Measurements ◽

Flux Layer ◽

The Baltic

Abstract. The estimation of CO2 exchange between the ocean and the atmosphere is essential to understand the global carbon cycle. The eddy-covariance technique offers a very direct approach to observe these fluxes. The turbulent CO2 flux is measured, as well as the sensible and latent heat flux and the momentum flux, a few meters above the ocean in the atmosphere. Assuming a constant-flux layer in the near-surface part of the atmospheric boundary layer, this flux equals the exchange flux between ocean and atmosphere. The purpose of this paper is the comparison of long-term flux measurements at two different heights above the Baltic Sea to investigate this assumption. The results are based on a 1.5-year record of quality-controlled eddy-covariance measurements. Concerning the flux of momentum and of sensible and latent heat, the constant-flux layer theory can be confirmed because flux differences between the two heights are insignificantly small more than 95 % of the time. In contrast, significant differences, which are larger than the measurement error, occur in the CO2 flux about 35 % of the time. Data used for this paper are published at http://doi.pangaea.de/10.1594/PANGAEA.808714.

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Vertical divergence of the atmospheric momentum flux near the sea surface at a coastal site

Journal of Physical Oceanography ◽

10.1175/jpo-d-21-0081.1 ◽

2021 ◽

Author(s):

L. Mahrt ◽

Erik Nilsson ◽

Anna Rutgersson ◽

Heidi Pettersson

Keyword(s):

Momentum Flux ◽

Sea Surface ◽

Layer Depth ◽

The Baltic Sea ◽

Wide Range ◽

Vertical Divergence ◽

Relative Stress ◽

Flux Measurements ◽

The Baltic ◽

The Impact

AbstractMotivated by previous studies, we examine the underestimation of the sea-surface stress due to the stress divergence between the surface and the atmospheric observational level. We analyze flux measurements collected over a six-year period at a coastal tower in the Baltic Sea encompassing a wide range of fetch values. Results are posed in terms of the vertical divergence of the stress scaled by the stress at the lowest observational level. The magnitude of this relative stress divergence increases with increasing stability and decreases with increasing instability, possibly partly due to the impact of stability on the boundary-layer depth. The magnitude of the relative stress divergence increases modestly with decreasing wave age. The divergence of the heat flux is not well correlated with the divergence of the momentum flux evidently due to the greater influence of advection on the temperature. Needed improvement of the conceptual framework and needed additional measurements are noted.

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

Ocean Science ◽

10.5194/os-15-235-2019 ◽

2019 ◽

Vol 15 (2) ◽

pp. 235-247 ◽

Cited By ~ 2

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.

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