scholarly journals Surfactant control of gas transfer velocity along an offshore coastal transect: results from a laboratory gas exchange tank

2016 ◽  
Vol 13 (13) ◽  
pp. 3981-3989 ◽  
Author(s):  
R. Pereira ◽  
K. Schneider-Zapp ◽  
R. C. Upstill-Goddard
Keyword(s):  
Organic Matter ◽  
Gas Exchange ◽  
Trace Gas ◽  
Gas Transfer ◽  
Transfer Velocity ◽  
Chl A ◽  
Gas Transfer Velocity ◽  
Biogeochemical Models ◽  
Sea Surface Microlayer ◽  
Laboratory Water

Abstract. Understanding the physical and biogeochemical controls of air–sea gas exchange is necessary for establishing biogeochemical models for predicting regional- and global-scale trace gas fluxes and feedbacks. To this end we report the results of experiments designed to constrain the effect of surfactants in the sea surface microlayer (SML) on the gas transfer velocity (kw; cm h−1), seasonally (2012–2013) along a 20 km coastal transect (North East UK). We measured total surfactant activity (SA), chromophoric dissolved organic matter (CDOM) and chlorophyll a (Chl a) in the SML and in sub-surface water (SSW) and we evaluated corresponding kw values using a custom-designed air–sea gas exchange tank. Temporal SA variability exceeded its spatial variability. Overall, SA varied 5-fold between all samples (0.08 to 0.38 mg L−1 T-X-100), being highest in the SML during summer. SML SA enrichment factors (EFs) relative to SSW were  ∼  1.0 to 1.9, except for two values (0.75; 0.89: February 2013). The range in corresponding k660 (kw for CO2 in seawater at 20 °C) was 6.8 to 22.0 cm h−1. The film factor R660 (the ratio of k660 for seawater to k660 for “clean”, i.e. surfactant-free, laboratory water) was strongly correlated with SML SA (r ≥ 0.70, p ≤ 0.002, each n = 16). High SML SA typically corresponded to k660 suppressions  ∼  14 to 51 % relative to clean laboratory water, highlighting strong spatiotemporal gradients in gas exchange due to varying surfactant in these coastal waters. Such variability should be taken account of when evaluating marine trace gas sources and sinks. Total CDOM absorbance (250 to 450 nm), the CDOM spectral slope ratio (SR = S275 − 295∕S350 − 400), the 250 : 365 nm CDOM absorption ratio (E2 : E3), and Chl a all indicated spatial and temporal signals in the quantity and composition of organic matter in the SML and SSW. This prompts us to hypothesise that spatiotemporal variation in R660 and its relationship with SA is a consequence of compositional differences in the surfactant fraction of the SML DOM pool that warrants further investigation.

scholarly journals Evidence for surface organic matter modulation of air-sea CO<sub>2</sub> gas exchange

2009 ◽  
Vol 6 (6) ◽  
pp. 1105-1114 ◽  
Author(s):  
M. Ll. Calleja ◽  
C. M. Duarte ◽  
Y. T. Prairie ◽  
S. Agustí ◽  
G. J. Herndl
Keyword(s):  
Organic Matter ◽  
Wind Speed ◽  
Gas Exchange ◽  
Co2 Exchange ◽  
Open Ocean ◽  
Gas Transfer ◽  
Co2 Fluxes ◽  
Transfer Velocity ◽  
Gas Transfer Velocity

Abstract. Air-sea CO2 exchange depends on the air-sea CO2 gradient and the gas transfer velocity (k), computed as a function of wind speed. Large discrepancies among relationships predicting k from wind suggest that other processes also contribute significantly to modulate CO2 exchange. Here we report, on the basis of the relationship between the measured gas transfer velocity and the organic carbon concentration at the ocean surface, a significant role of surface organic matter in suppressing air-sea gas exchange, at low and intermediate winds, in the open ocean, confirming previous observations. The potential role of total surface organic matter concentration (TOC) on gas transfer velocity (k) was evaluated by direct measurements of air-sea CO2 fluxes at different wind speeds and locations in the open ocean. According to the results obtained, high surface organic matter contents may lead to lower air-sea CO2 fluxes, for a given air-sea CO2 partial pressure gradient and wind speed below 5 m s−1, compared to that observed at low organic matter contents. We found the bias in calculated gas fluxes resulting from neglecting TOC to co-vary geographically and seasonally with marine productivity. These results support previous evidences that consideration of the role of organic matter in modulating air-sea CO2 exchange may improve flux estimates and help avoid possible bias associated to variability in surface organic concentration across the ocean.

scholarly journals Evidence for surface organic matter modulation of air-sea CO<sub>2</sub> gas exchange

2008 ◽  
Vol 5 (6) ◽  
pp. 4209-4233
Author(s):  
M. Ll. Calleja ◽  
C. M. Duarte ◽  
Y. T. Prairie ◽  
S. Agustí ◽  
G. J. Herndl
Keyword(s):  
Organic Matter ◽  
Wind Speed ◽  
Gas Exchange ◽  
Ocean Surface ◽  
Co2 Exchange ◽  
Gas Transfer ◽  
Co2 Fluxes ◽  
Transfer Velocity ◽  
Gas Transfer Velocity

Abstract. Air-sea CO2 exchange depends on the air-sea CO2 gradient and the gas transfer velocity (k), computed as a simple function of wind speed. Large discrepancies among relationships predicting k from wind suggest that other processes may also contribute significantly to modulate CO2 exchange. Here we report, on the basis of the relationship between the measured gas transfer velocity and the ocean surface organic carbon concentration at the ocean surface, a significant role of surface organic matter in suppressing air-sea gas exchange, at low and intermediate winds, in the open ocean. The potential role of total surface organic matter concentration (TOC) on gas transfer velocity (k) was evaluated by direct measurements of air-sea CO2 fluxes at different wind speeds and locations in the open ocean. According to the results obtained, high surface organic matter contents may lead to lower air-sea CO2 fluxes, for a given air-sea CO2 partial pressure gradient and wind speed below 5 m s−1, compared to that observed at low organic matter contents. We found the bias in calculated gas fluxes resulting from neglecting TOC to co-vary geographically and seasonally with marine productivity. These findings suggest that consideration of the role of organic matter in modulating air-sea CO2 exchange can improve flux estimates and help avoid possible bias associated to variability in surface organic concentration across the ocean.

scholarly journals Sea-to-air and diapycnal nitrous oxide fluxes in the eastern tropical North Atlantic Ocean

2012 ◽  
Vol 9 (3) ◽  
pp. 957-964 ◽  
Author(s):  
A. Kock ◽  
J. Schafstall ◽  
M. Dengler ◽  
P. Brandt ◽  
H. W. Bange
Keyword(s):  
Nitrous Oxide ◽  
Gas Exchange ◽  
Mixed Layer ◽  
North Atlantic Ocean ◽  
Gas Transfer ◽  
Potential Contribution ◽  
Transfer Velocity ◽  
N2o Production ◽  
Gas Transfer Velocity ◽  
Upwelled Water

Abstract. Sea-to-air and diapycnal fluxes of nitrous oxide (N2O) into the mixed layer were determined during three cruises to the upwelling region off Mauritania. Sea-to-air fluxes as well as diapycnal fluxes were elevated close to the shelf break, but elevated sea-to-air fluxes reached further offshore as a result of the offshore transport of upwelled water masses. To calculate a mixed layer budget for N2O we compared the regionally averaged sea-to-air and diapycnal fluxes and estimated the potential contribution of other processes, such as vertical advection and biological N2O production in the mixed layer. Using common parameterizations for the gas transfer velocity, the comparison of the average sea-to-air and diapycnal N2O fluxes indicated that the mean sea-to-air flux is about three to four times larger than the diapycnal flux. Neither vertical and horizontal advection nor biological production were found sufficient to close the mixed layer budget. Instead, the sea-to-air flux, calculated using a parameterization that takes into account the attenuating effect of surfactants on gas exchange, is in the same range as the diapycnal flux. From our observations we conclude that common parameterizations for the gas transfer velocity likely overestimate the air-sea gas exchange within highly productive upwelling zones.

Is remote sensing of the surfactant effect on gas transfer velocity possible?

2021 ◽  
Author(s):  
Jacek Piskozub ◽  
Violetta Drozdowska ◽  
Iwona Wróbel-Niedźwiecka ◽  
Przemysław Makuch ◽  
Piotr Markuszewski ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Wind Speed ◽  
Gas Exchange ◽  
Partial Pressure ◽  
Gas Transfer ◽  
Transfer Velocity ◽  
Fluorescence Parameters ◽  
Gas Transfer Velocity ◽  
Surfactant Effect ◽  
Surfactant Activity

&lt;p&gt;The air-sea gas flux is proportional to the difference of partial pressure between the sea-water and the overlying atmosphere multiplied by gas transfer velocity &lt;em&gt;k&lt;/em&gt;, a measure of the effectiveness of the gas exchange. Because wind is the source of turbulence making the gas exchange more effective, &lt;em&gt;k&lt;/em&gt; is usually parameterized by wind speed. Unfortunately, measured values of gas transfer velocity at a given wind speed have a large spread in values. Surfactants have been long suspected as the main reason of this variability but few measurements of gas exchange and surfactants have been performed at open sea simultaneously and therefore their results were inconclusive. Only recently, it has been shown that surfactants may decrease the CO&lt;sub&gt;2&lt;/sub&gt; air-sea exchange by up to 50%. However the labour intensive methods used for surfactant study make it impossible to collect enough data to map the surfactant coverage or even create a gas transfer velocity parameterization involving a measure of surfactant activity. This is why we propose to use optical fluorescence as a proxy of surfactant activity.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Previous research done by our group showed that fluorescence parameters allow estimation the surfactant enrichment of the surface microlayer, as well as types and origin of fluorescent organic matter involved. We plan to measure, from a research ship, all the variables needed for calculation of gas transfer velocity &lt;em&gt;k&lt;/em&gt; (namely CO&lt;sub&gt;2&lt;/sub&gt; partial pressure both in water and in air as well as vertical flux of this trace gas) and to use mathematical optimization methods to look for a parameterization involving wind speed and one of the fluorescence parameters which will minimize the residual &lt;em&gt;k&lt;/em&gt; variability. Although our research will still involve water sampling and laboratory fluorescence measurements, the knowledge of which absorption and fluorescence emission bands are the best proxy for surfactant activity may allow to create remote sensing products (fluorescence lidars) allowing continuous measurements of surfactant activity at least from the ship board, if not from aircraft and satellites. The improved parameterization of the CO&lt;sub&gt;2&lt;/sub&gt; gas transfer velocity will allow better constraining of basin-wide and global air-sea fluxes, an important component of global carbon budget.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;If an improved gas transfer velocity parametrization based on surfactant fluorescence spectrum in concert with a turbulence proxy (wind) were to be found, a tantalizing possibility arises of a remote sensing estimation of &lt;em&gt;k&lt;/em&gt;. Namely a UV lidar can both excite and measure the fluorescence band identified as proxy of the surfactant effect on the gas transfer velocity. Depending on the wavelength bands needed to be utilized, the effect could be measured from a moving ship (already an improvements on methods needing sampling), an aircraft or possibly even a satellite. We intend to pursue this idea in cruises to both the Baltic and the North Atlantic, possibly in cooperation with other air-sea interaction groups (this presentation is in part an invitation to cooperation).&lt;/p&gt;

Gas Exchange in Rivers and Estuaries: Choosing a Gas Transfer Velocity

Estuaries ◽  
2001 ◽  
Vol 24 (2) ◽  
pp. 312 ◽  
Author(s):  
Peter A. Raymond ◽  
Jonathan J. Cole
Keyword(s):  
Gas Exchange ◽  
Gas Transfer ◽  
Transfer Velocity ◽  
Gas Transfer Velocity

scholarly journals Sea-to-air and diapycnal nitrous oxide fluxes in the eastern tropical North Atlantic Ocean

2011 ◽  
Vol 8 (5) ◽  
pp. 10229-10246 ◽  
Author(s):  
A. Kock ◽  
J. Schafstall ◽  
M. Dengler ◽  
P. Brandt ◽  
H. W. Bange
Keyword(s):  
Nitrous Oxide ◽  
Gas Exchange ◽  
Mixed Layer ◽  
North Atlantic Ocean ◽  
Gas Transfer ◽  
Potential Contribution ◽  
Transfer Velocity ◽  
N2o Production ◽  
Gas Transfer Velocity ◽  
Upwelled Water

Abstract. Sea-to-air and diapycnal fluxes of nitrous oxide (N2O) into the mixed layer were determined during three cruises to the upwelling region off Mauritania. Both fluxes were elevated close to the shelf break, but elevated sea-to-air fluxes reached further offshore as a result of the offshore transport of upwelled water masses. To calculate a mixed layer budget for N2O we compared the regionally averaged sea-to-air and diapycnal fluxes and estimated the potential contribution of other processes, such as vertical advection and biological N2O production in the mixed layer. Using common parameterizations for the gas transfer velocity, the comparison of the average sea-to-air and diapycnal N2O fluxes indicated that the mean sea-to-air flux is about three to four times larger than the diapycnal flux. Vertical and horizontal advection or biological production were found not sufficient to close the mixed layer budget. Instead, the sea-to-air flux, calculated using a parameterization that takes into account the attenuating effect of surfactants on gas exchange, is in the same range as the diapycnal flux. This indicates that common parameterizations for the gas transfer velocity might overestimate the air-sea gas exchange within highly productive upwelling zones.

scholarly journals Changes in gross oxygen production, net oxygen production, and air-water gas exchange during seasonal ice melt in the Bras d'Or Lake, a Canadian estuary

2017 ◽  
Author(s):  
Cara C. Manning ◽  
Rachel H. R. Stanley ◽  
David P. Nicholson ◽  
Brice Loose ◽  
Ann Lovely ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Open Water ◽  
Gas Transfer ◽  
Polar Regions ◽  
Oxygen Production ◽  
Transfer Velocity ◽  
Gas Transfer Velocity ◽  
Ice Melt ◽  
Wide Range ◽  
Water Gas

Abstract. Sea ice is an important control on gas exchange and primary production in polar regions. We measured net oxygen production and gross oxygen production using near-continuous measurements of the O2 / Ar gas ratio and discrete measurements of the triple isotopic composition of O2 in the Bras d'Or Lake, an estuary in Nova Scotia, Canada, as the bay transitioned from ice-covered to ice-free conditions. The volumetric gross oxygen production was 5.4(+2.8−1.6) mmol O2 m−3 d−1, similar at the beginning and end of the time-series, and likely peaked at the end of the ice melt period. Net oxygen production displayed more temporal variability and the system was on average net autotrophic during ice melt and net heterotrophic following the ice melt. We performed the first field-based dual tracer release experiment in ice-covered water to quantify air-water gas exchange. The gas transfer velocity at > 90 % ice cover was 6 % of the rate for nearly ice-free conditions. Published studies have shown a wide range of results for gas transfer velocity in the presence of ice, and this study indicates that gas transfer through ice is much slower than the rate of gas transfer through open water. The results also indicate that both primary producers and heterotrophs are active in Whycocomagh Bay during spring while it is covered in ice.

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