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

Lookup NU author(s): Dr Ryan Pereira, Dr Klaus Schneider-Zapp, Professor Robert Upstill-Goddard

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

We measured total surfactant activity (SA; Triton T-X-100 equivalent) and CDOM absorbance (cm-1) in thesurface microlayer (SML) and subsurface water (SSW) seasonally (2012-2013) along a 20 km coastal transect(North East UK), and evaluated corresponding values of the gas transfer velocity (kw; cm hr-1) using a customdesigned air-sea gas exchange tank. Spatial SA variability exceeded its temporal variability. Overall, SA variedfive-fold between all samples (0.08 - 0.38 mg L-1 T-X-100), being highest in the SML during summer. SML SAenrichment factors relative to SSW were ~ 1.0 - 1.9, except for two values (0.75; 0.89: February 2013). CDOMabsorbance (250 - 450 nm), the CDOM spectral slope ratio (SR = S275–295 / S350–400) and the 250:365 nm CDOMabsorbance ratio (E2 : E3) demonstrate the potential for terrestrially-derived CDOM to be biogeochemically processed in North Sea coastal waters. The range in corresponding k660 (kw for CO2; freshwater; 20 oC) was 6.8 -22.0 cm hr-1. The film factor R660 (the ratio of the scaled transfer velocity k660 to the one of clean water) stronglycorrelates with SA (r ≥0.70, p ≤0.002, each n = 16) with high SML SA correlated to k660 suppression ~14 - 51 %relative to clean laboratory water, highlighting strong spatio-temporal gradients in gas exchange due to varyingsurfactant in these coastal waters. Such variability should be taken account of when evaluating marine trace gassources and sinks.


Publication metadata

Author(s): Pereira R, Schneider-Zapp K, Upstill-Goddard RC

Publication type: Article

Publication status: Published

Journal: Biogeosciences

Year: 2016

Volume: 13

Issue: 13

Pages: 3981-3989

Print publication date: 18/01/2016

Online publication date: 18/01/2016

Acceptance date: 24/06/2016

ISSN (print): 1726-4170

ISSN (electronic): 1726-4189

Publisher: Copernicus GmbH

URL: http://dx.doi.org/10.5194/bg-13-3981-2016

DOI: 10.5194/bg-13-3981-2016


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