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

Abstract

Abstract. The effect of ocean acidification and changing water conditions on primary (and secondary) 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 3 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 2 to simulate the 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 (10-400 nm). Comparing results obtained during pre-bloom and oligotrophic conditions, we find the same four lognormal modal diameters (18.5± 0.6, 37.5± 1.4, 91.5± 2.0, 260± 3.2 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 (transparent exopolymeric particles), chlorophyll a and other pigments. Organic fractions determined from kappa closure calculations for the diameter, D p ∼ 50 nm, were much larger during the pre-bloom period (64 %) than during the oligotrophic period (38 %), and the organic fraction decreased as the particle size increased. Combining data from both campaigns together, strong positive correlations were found between the organic fraction of the aerosol and chlorophyll a 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.Published by Copernicus Publications on behalf of the European Geosciences Union. Partial pressure of CO 2 , pCO 2 , 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.

Optical, physical and chemical properties of aerosols transported to a coastal site in the western Mediterranean: a focus on primary marine aerosols

“…The log-normal modes (four modes with diameters of 0.04, 0.13, 1.2 and 5.4 µm) found for these PMA were in agreement with previous measurement made by Ovadnevaite et al (2014) and Schwier et al (2015). The PMA episode was also influenced by fine particles, denoted by the high number concentration of fine particle and by an Ångström exponent varying between 0.4 and 2.…”

“…We find a good agreement of modal diameters with the size distribution measured by Ovadnevaite et al (2014) in the parameterisation of the emission of PMA from the Atlantic Ocean. Furthermore, our results agree with measurements taken in the Mediterranean Sea by Schwier et al (2015). We observed a high number concentration of fine particles during the PMA period, which is consistent with measurements reported in Fig.…”

“…This mode was also measured by Schwier et al (2015) at d = 37.5 nm ± 1.4 during PMA flux measurements from Mediterranean waters. The second mode has a modal diameter of 130 nm, which is somewhat higher than the 90 nm mode found by Schwier et al (2015), which is related to the presence of aged particles during our study. We find important distinctions between the three different periods reported in Fig.…”

Climate Feedback on Aerosol Emission and Atmospheric Concentrations

“…They suggest that the termination of a phytoplankton bloom releases large quantities of organic material such as transparent exopolymer particles, which form surface films and may be transferred into the marine aerosol. In contrast, strong correlation of organic aerosol and chlorophyll-a has been found in Mediterranean field measurements [68]. Since plankton productivity as well as species composition responds to changing climatic conditions, this connection should be clarified before believable conclusions on the potential change in organic marine aerosol for changing climates can be drawn.…”

Modelling organic aerosol concentrations and properties during ChArMEx summer campaigns of 2012 and 2013 in the western Mediterranean region

“…Recently derived parameterisations (Gantt et al, 2012;Schwier et al, 2015) relate the organic fraction of sea-salt emissions to the seawater chlorophyll a (chl a) concentrations. However, the contribution of these species to the organic budget over the Mediterranean Sea is not clear.…”