Primary marine aerosol emissions from the Mediterranean Sea during pre-bloom and oligotrophic conditions: correlations to seawater chlorophyll a from a mesocosm study

A. N. Schwier, C. Rose, E. Asmi, A. M. Ebling, W. M. Landing, S. Marro, M.-L. Pedrotti, A. Sallon, F. Iuculano, S. Agusti, A. Tsiola, P. Pitta (+4 others)
2014 Atmospheric Chemistry and Physics Discussions  
The effect of ocean acidification and changing water conditions on primary marine aerosol emissions is not well understood on a regional or a global scale. To investigate this effect as well as the indirect effect on aerosol that changing biogeochemical parameters can have, ~52 m<sup>3</sup> pelagic mesocosms were deployed for several weeks in the Mediterranean Sea during both winter pre-bloom and summer oligotrophic conditions and were subjected to various levels of CO<sub>2</sub> to simulate
more » ... he conditions foreseen in this region for the coming decades. After seawater sampling, primary bubble-bursting aerosol experiments were performed using a plunging water jet system to test both chemical and physical aerosol parameters. Comparing results obtained during pre-bloom and oligotrophic conditions, we find the same four log-normal modal diameters (18.5, 37.5, 91.5, 260 nm) describing the aerosol size distribution during both campaigns, yet pre-bloom conditions significantly increased the number fraction of the second (Aitken) mode, with an amplitude correlated to virus-like particles, heterotrophic prokaryotes, TEPs, chlorophyll <i>a</i> and other pigments. Organic fractions determined from κ closure calculations for <i>D</i><sub>p</sub> ~50 nm were much larger during the pre-bloom period (64%) than during the oligotrophic period (38%), and the organic fraction increased as the particle size decreased. Combining data from both campaigns together, strong positive correlations were found between the organic fraction of the aerosol and chlorophyll <i>a</i> concentrations, heterotrophic and autotrophic bacteria abundance, and dissolved organic carbon (DOC) concentrations. As a consequence of the changes in the organic fraction and the size distributions between pre-bloom and oligotrophic periods, we find that the ratio of cloud condensation nuclei (CCN) to condensation nuclei (CN) slightly decreased during the pre-bloom period. The enrichment of the seawater samples with microlayer samples did not have any effect on the size distribution, organic content or the CCN activity of the generated primary aerosol. <i>p</i>CO<sub>2</sub> perturbations had little effect on the physical or chemical parameters of the aerosol emissions, with larger effects observed due to the differences between a pre-bloom and oligotrophic environment.
doi:10.5194/acpd-14-26187-2014 fatcat:7icx7u2ckrfq7muhadqhemvgjy