Stable isotopes measurements reveal dual carbon pools contributing to organic matter enrichment in marine aerosol

Stable carbon isotope ratios in marine aerosol collected over the Southern Indian Ocean revealed delta C-13 values ranging from -20.0% to -28.2%. The isotope ratios exhibited a strong correlation with the fractional organic matter (OM) enrichment in sea spray aerosol. The base-level isotope ratio of -20.0% is characteristic of an aged Dissolved Organic Matter (DOM) pool contributing a relatively homogeneous background level of DOM to oceanic waters. The range of isotope ratios, extending down to -28.2%, is characteristic of more variable, stronger, and fresher Particulate Organic Matter (POM) pool driven by trophic level interactions. We present a conceptual dual-pool POM-DOM model which comprises a 'young' and variable POM pool which dominates enrichment in sea-spray and an 'aged' but invariant DOM pool which is, ultimately, an aged end-product of processed 'fresh' POM. This model is harmonious with the preferential enrichment of fresh colloidal and nano-gel lipid-like particulate matter in sea spray particles and the observed depleted delta C-13 ratio resulting from isotope equilibrium fractionation coupled with enhanced plankton photosynthesis in cold water (-2 degrees C to + 8 degrees C). These results re-assert the hypothesis that OM enrichment in sea-spray is directly linked to primary production and, consequently, can have implications for climate-aerosol-cloud feedback systems.