New index of organic mass enrichment in sea spray aerosols linked with senescent status in marine phytoplankton

Linking the amount of organic matter (OM) in sea spray aerosols (SSAs) to biological processes in ocean surface is essential for understanding marine aerosol formation and their potential to affect cloud formation. To date, chlorophyll (Chl) a concentration has been widely used as a surrogate for surface phytoplankton biomass or productivity to predict the relative abundance of OM in SSAs (OM(SSA)). Here we show a new index to present OM(SSA) using concentrations of Chl a and chlorophyllide (Chllide) a, which is a breakdown product of Chl a and has been used as a biomarker of senescent algal cells. The index was compared with submicrometer OM(SSA), based on surface seawater and aerosol samples obtained during the pre-bloom in the western subarctic Pacific. Our results showed that the OM(SSA) was highly correlated with this unique index, suggesting that the OM(SSA) was closely linked with senescent algal cells and/or cell lysis. Furthermore, the hygroscopicity parameters κ derived from water-extracted SSA samples implied a reduction in the SSA hygroscopicity with increasing senescent status of phytoplankton. The index can represent OM(SSA) on a timescale of a day during the pre-bloom period, which should be further examined over different oceanic regions.