Abstract
The export of organic matter from ocean to atmosphere represents a substantial carbon flux in the Earth system, yet the impact of environmental drivers on this transfer is not fully understood. This work presents dissolved and particulate organic carbon (DOC, POC) concentrations, their enrichment factors in the sea surface microlayer (SML), and equivalent measurements in marine aerosol particles across the Atlantic Ocean. DOC concentrations averaged 161 ± 139 µmol L–1 (n = 78) in bulk seawater and 225 ± 175 µmol L–1 (n = 79) in the SML; POC concentrations averaged 13 ± 11 µmol L–1 (n = 80) and 17 ± 10 µmol L–1 (n = 80), respectively. High DOC and POC enrichment factors were observed when samples had low concentrations, and lower enrichments when concentrations were high. The impacts of wind speed and chlorophyll-a levels on concentrations and enrichment of DOC and POC in seawater were insignificant. In ambient submicron marine aerosol particles the concentration of water-soluble organic carbon was approximately 0.2 µg m–3. Water-insoluble organic carbon concentrations varied between 0.01 and 0.9 µg m–3, with highest concentrations observed when chlorophyll-a concentrations were high. Concerted measurements of bulk seawater, the SML and aerosol particles enabled calculation of enrichment factors of organic carbon in submicron marine ambient aerosols, which ranged from 103 to 104 during periods of low chlorophyll-a concentrations and up to 105 when chlorophyll-a levels were high. The results suggest that elevated local biological activity enhances the enrichment of marine-sourced organic carbon on aerosol particles. However, implementation of the results in source functions based on wind speed and chlorophyll-a concentrations underestimated the organic fraction at low biological activity by about 30%. There may be additional atmospheric and oceanic parameters to consider for accurately predicting organic fractions on aerosol particles.
Highlights
The oceans are a significant source of marine aerosol particles which may impact the radiation budget of the earth directly by scattering and absorbing solar radiation and indirectly by affecting cloud formation processes
Organic carbon was enriched in the surface microlayer (SML) by a factor
following a pattern that may be explained by a surface saturation effect
Summary
The oceans are a significant source of marine aerosol particles which may impact the radiation budget of the earth directly by scattering and absorbing solar radiation and indirectly by affecting cloud formation processes. In a conceptual relationship Gantt et al (2011) proposed that, besides aerosol size, wind speed and b iological activity (as reflected in chl-a concentrations) are the most important parameters regulating the organic matter content of primary aerosol particles (particles that are generated at the ocean surface, often referred to as sea spray aerosol or SSA) Based on this model it is predicted that highest organic enrichment in SSA particles occurs at low wind conditions when marine aerosol production is minimal and the SML covers the ocean surface. In order to investigate the influence of biogeochemical parameters, the organic carbon concentrations (in the SML, bulk water and aerosol particles) were analyzed as functions of chl-a concentration and wind speed to determine if and van Pinxteren et al: The influence of environmental drivers on the enrichment of organic carbon in the sea surface microlayer and in submicron aerosol particles – measurements from the Atlantic Ocean. Within these two transects regions in the tropical climate zone (CVAO) and the temperate climate zone (Bergen), as well as a large part of the Atlantic Ocean, are covered
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