Surfactant Photo-Reactivity and Air-Sea Gas Exchange
Abstract
Uncertainty over gas transfer velocity (kw) variability is one of the greatest challenges in quantifying net global air-sea gas exchange. Accumulation of amphiphylic surfactants in the sea-surface microlayer (SML) can dampen kw by up to 55%. Low surfactant enrichments at low wind speeds may suggest surfactant photo-degradation in the SML, but the consequent effect on kw remains unquantified. This research explores the impact of surfactant photochemistry on air-sea gas exchange through modification of kw. The SML and underlying water (ULW) were sampled monthly along a 20-km transect in coastal North Sea from February to July 2015. SML surfactant activity (SA) showed strong spatial variability, decreasing seaward, most likely reflecting river inputs. ULW SA showed strong temporal variability, reflecting the development of the phytoplankton bloom. Surfactant enrichment factors (EF) were ≥ 1 during the sampling period, and highest EFs occurred during the most turbulent conditions. Evidently the SML retains its integrity over a range of environmental conditions. Preliminary irradiations on 0.2 μm filtered ULW samples showed variable changes in SA over time; filtration can remove a significant portion of surfactants but some precursors remain. In 53% of experiments the irradiated ULW showed higher SA than the dark control, and in 47% the dark control SA was higher than the irradiated sample. These variations may be due to abiotic cross-linking, which can still occur in the dark and may be masking any photochemical changes occurring. Further irradiations of unfiltered seawater will follow, as well as gas exchange tank experiments where natural and irradiated surfactants will be used to determine the effect of surfactant photochemistry on kw. These data will contribute to further parameterisation of kw and ultimately to global climate change research.
- Publication:
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American Geophysical Union, Ocean Sciences Meeting
- Pub Date:
- February 2016
- Bibcode:
- 2016AGUOS.A24C2609R
- Keywords:
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- 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4815 Ecosystems;
- structure;
- dynamics;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4840 Microbiology and microbial ecology;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4504 Air/sea interactions;
- OCEANOGRAPHY: PHYSICAL