Exploratory Study of the Formation and Distribution of Surfactant Films on the Ocean's Surface and Their Global Mapping
Final Report Abstract
Results from a study of surfactants in the sea-surface microlayer (SML) in different regions of the ocean (subtropical, temperate, polar) suggest that this interfacial layer between the ocean and atmosphere covers the ocean’s surface to a significant extent. Threshold values at which primary production acts as a significant source of natural surfactants to the surface have been derived from the enrichment of surfactants in the SML relative to underlying water and local primary production. Similarly, we have also derived a wind speed threshold at which the SML is likely to be disrupted. Global maps of primary production and wind speed are used to estimate the ocean’s SML coverage. Earlier work by Asher (1997) and Tasi and Lui (2003) assessed the effect of the SML on global air-sea CO2 fluxes using global ocean primary productivity maps and suggested that the annual net flux is reduced by at least 20%. However, the authors chose somewhat arbitrary threshold values of local primary production as an indicator for the presence of surfactant films with the assumption enrichment (i.e. intensity of SML formation) increases with primary production. However, the results from this study suggest that surfactant enrichment in the SML is typically greater in oligotrophic regions of the ocean than in more productive waters leading to a higher extent of coverage. Furthermore, the enrichment of surfactants persisted at wind speeds of up to 10 m s^-1 without any observed depletion above 5 m s^-1 . This suggests that the SML is stable enough to exist above at the global average wind speed of 6.6 m s^-1 . However, compared to the earlier assessments by Asher (1997) and Tsai and Lui (2003), this study suggests that the Southern Ocean is typically free of SML due to disruption by wind forces exceeding 10 m s^-1. Concentrations of surfactants and carbohydrates in the oceanic SML are generally exceeding 0.5 mg L^-1 and 0.2 mg-C L^-1 respectively, at which most of the decrease in transfer velocities of gases between the ocean and atmosphere occurs (Hypothesis 2). Overall, this study indicates that the impact of the SML on air-sea gas exchange and marine carbon cycle is likely of global significance, although the limited data set do not allow quantitative assessments. However, the study justifies the incorporation of the SML in international oceanographic programs, or even to establish new programs to investigate effects of the SML in oceanic processes within regional and global scales. New York Times, 28 July 2009, “Scientists Find a Microbe Haven at Ocean’s Surface” http://www.nytimes.com/2009/07/28/science/28ocea.html
Publications
- 2009. The distribution and fate of surface-active substances in the sea-surface micro layer and water column. Mar. Chem. 115, 1-9.
Wurl, O., Miller, L., Röttgers, R., Vagle, S.
- 2009. The distribution and fate of surface-active substances in the sea-surface microlayer and water column. Mar Chem, 115, 1-9
Wurl, O., Miller, L., Röttgers, R., Vagle, S.
- Practical Guidelines for the Analysis for Seawater. CRC Press, Boca Raton, FL. 2009
Wurl, O
- 2011. Formation and global distribution of sea-surface microlayers. Biogeosciences 8, 121-135.
Wurl, O., Wurl, E., Miller, L., Johnson, K., Vagle, S.
- 2011. Production and fate of transparent exopolymer particles (TEP) in the ocean. J. Geophys. Res. 116, C00H13
Wurl, O., Miller, L., Vagle, S.
(See online at https://doi.org/10.1029/2011JC007342)
