Zooplankton grazing increases atmospheric primary aerosol production in the high Arctic

Abstract

The rapidly changing Arctic has led to evolving natural aerosol emissions, which have strong feedback effects on its climate system. Sea spray aerosol (SSA) particles are a main source of aerosols; they influence cloud formation and cloud properties. Ocean microbiota potentially have an impact on SSA production and flux, but our understanding of the mechanisms is still limited. The potential impact of ocean microbiota on SSA fluxes is still a matter of active research. In this multidisciplinary study conducted in the central Arctic during The Multidisciplinary Drifting Observatory for the Study of Arctic Climate expedition, air-sea interactions were measured by means of in situ bubble-bursting experiments. For the first time, we studied the effect of zooplankton grazing on aerosol production. We found that surface water subjected to zooplankton grazing had a 2-fold increase in SSA production relative to controls without zooplankton. Our biogeochemical results suggest that fresh organic material-possibly dissolved organic carbon and dissolved organic nitrogen from humic-like substances-influences aerosol production. We find a strong chemical-selective process affecting SSA production, with humic-like substances much enriched (40%-280%) relative to protein-like material in the aerosol relative to the water. Our results point to a complex relationship between specific low-concentration organic components in the water phase and its relative capability of being aerosolized, with strong chemically selective processes affecting SSA production. We provide evidence for the role of zooplankton, implying a complex microbial loop that may be regulating the organic component of the SSA production. This study underlines the role of zooplankton in biogeochemical cycles, due to their large biomass and transformation of organic matter during feeding and digestion. Similar processes may occur in other regions with high zooplankton grazing impact, for example, in productive parts of the Southern Ocean and in upwelling regions.