Ecological modeling of marine biogenic isoprene (C5H8) emissions in the Southern Ocean

Abstract

The the strength and direction of the aerosol-induced radiative climate forcing in the atmosphere is one of the biggest uncertainty sources in global warming projections. In the pristine polar marine atmosphere of the Southern Ocean (SO), where cloud formation processes are strongly influenced by aerosol emissions, an important part of particle formation occurs due to the oxidation of biogenic trace gases emitted by the sea. Isoprene (C5H8) is a is a volatile organic compound (VOC) produced eminently by phytoplankton species in the oceans and is a precursor of secondary organic aerosol (SOA). In this work, for the first time, we implemented the isoprene production rates of diatoms, coccolithophores and other phytoplankton species into a high-resolution SO set-up of the regional mechanistic marine ecosystem model ROMS-BEC. We calculated the annual integrated SO production and emission rates and found that the contribution of the SO phytoplankton to the global oceanic emission of isoprene is 0.332 (± 0.049) Gt C year-1, which equals, even surpass, some global oceanic estimates. We also found that isoprene emissions co-vary with the SO net primary production, and that diatoms are the main isoprene producers. Finally, in order to validate the model results, we used sea surface concentration data of isoprene, and associated environmental and ecosystem variables, recompiled from three different research cruises in the SO: “TransPEGASO” (South Atlantic Ocean), “PEGASO” (Weddell Sea, Oarkney Islands & South Georgia Islands) and “ACE Expedition” (complete circumnavigation of the SO)