Preliminary results on the correlation between biogenic aerosol and primary production in the Ross Sea – (PNRA-BioAPRoS Project)

The Biogenic Aerosol and Primary Production in the Ross Sea – BioAPRoS project, funded by funded by the Ministry for the Education, University and Scientific Research (MIUR) through the National Antarctic Research Programme (PNRA) aims to improve the understanding of the ocean-atmosphere interactions with particular attention to the interconnections between oceanic primary production and atmospheric gaseous and particulate compounds. These processes have a strong climatic relevance due to the aerosol interaction with solar radiation, its possible interaction with cloud formation and properties, in a region where other aerosol sources are very limited. To achieve the objectives of the project, measurements and sampling in the atmosphere (dimethylsulfide, in the gas phase, and methanesulfonic acid, sugars, amino acids and methoxyphenols in the aerosols) and in sea water (nutrients, chlorophyll, phytoplankton composition and physiological state, DMSP as a precursor of atmospheric DMS) were carried out simultaneously for the first time at the Italian "Mario Zucchelli" Station (MZS; 74.7°S, 164.1°E).

We report here the data obtained in two Antarctic field campaigns carried out in summers of 2018-19 and 2019-20. The DMS atmospheric concentration was measured directly in situ by Gas Chromatography.  It showed concentrations up to 921 pptv (the highest value obtained in both campaigns); the timing of maximum concentration was strongly related to the timing of sea ice melting in the surrounding oceanic areas. Within the project, the low-cost ACHAB (Antartic low-Cost Hydro Arduino Bio-optic profiler) probe has been developed for the acquisition of physical and bio-optical data along the water column, during the 2019-20 campaign. Furthermore, the Phyto-VFP (Phytoplankton Variable Fluorescence Production) bio-optical model was refined to be applied to the Southern Ocean for the estimation of primary production in Terranova Bay and Ross Sea at micro and mesoscale resolutions, respectively. Phyto-VFP was specifically set-up using as input chl a satellite data (merged products based on MODIS-A, MERIS, SeaWIFS, VIIRS-N for low resolution images and Sentinel-2 for high resolution ones) as well as the photosynthetic parameters obtained from a series of laboratory experiments conducted on polar species, enabling to take into account the effect of a nutrient limitation on their photosynthetic performance.

The evolution of concentration of the atmospheric compounds arising from phytoplankton activity was investigated with respect to oceanic parameters (chlorophyll and primary productivity, in turn related to the phytoplankton taxonomic composition and physiological state), to the variations of solar and photosynthetically active radiation, and to the dynamics of sea ice in the Ross Sea.

Understanding and quantifying the correlation between atmospheric compounds and oceanic primary productivity (affecting the oceanic and atmospheric CO₂ budget) has a relevant importance in studies on global change because this interaction is influenced by, and in its turn influences, climatic variations.