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 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 m3 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 CO2 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. 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 a and other pigments. Organic fractions determined from κ closure calculations for Dp ~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 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. pCO2 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.

Phytoplankton blooms weakly influence the cloud forming ability of sea spray aerosol

“…Measurements of hygroscopicity in laboratory experiments utilizing complex organic matrices like the present study and that ofFuentes et al [2011] lack full agreement with in situ SSA generation studies performed in the North Atlantic and the Mediterranean Sea[Schwier et al, 2015] (Figure 1b, gray markers). Measurements of hygroscopicity in laboratory experiments utilizing complex organic matrices like the present study and that ofFuentes et al [2011] lack full agreement with in situ SSA generation studies performed in the North Atlantic and the Mediterranean Sea[Schwier et al, 2015] (Figure 1b, gray markers).…”

“…While phytoplankton exudate production was likely the most influential process controlling organic matter composition in monoculture-based studies [Collins et al, 2013;Fuentes et al, 2011;Moore et al, 2011;Wex et al, 2010b], the bloom microcosm experiments presented in this study include biochemical processes (e.g., enzyme activity) that influence the organic matter dynamics throughout this type of experiment [Riemann et al, 2000]. Comparison of these two mesocosm/microcosm studies, along with the aforementioned comparison between the present study and those of Schwier et al [2015] and Quinn et al [2014], suggests that the specific chemical composition of organic matter may influence the relationship between κ app and marine microbial activity. Using a similar chemical system, prior laboratory studies have shown that bacterial processing could be important to SSA composition, mixing state, and physicochemical properties [Ault et al, 2013;Collins et al, 2013;Prather et al, 2013;Wang et al, 2015].…”

“…Based on the κ app values measured in this and comparable studies (Figure 1), the upper limit value of D act for nascent SSA would be 125 nm (s c = 0.1%, κ app = 0.7). Fuentes et al [2010a] and Schwier et al [2015] also showed that regions of the ocean with higher chl a led to a greater production flux of particles during in situ controlled SSA production experiments using plunging water jet systems. Fuentes et al [2010a] and Schwier et al [2015] also showed that regions of the ocean with higher chl a led to a greater production flux of particles during in situ controlled SSA production experiments using plunging water jet systems.…”

Modeling the biogeochemical impact of atmospheric phosphate deposition from desert dust and combustion sources to the Mediterranean Sea

“…Another important source of P aerosols in this region is sea spray (Querol et al, 2009;Grythe et al, 2014;Schwier et al, 2015). Sea spray aerosols over the Mediterranean mainly come from the Mediterranean itself with little contribution from the Atlantic Ocean.…”

First mesocosm experiments to study the impacts of ocean acidification on plankton communities in the NW Mediterranean Sea (MedSeA project)

“…The same cluster was also sampled by the mean of a Teflon pump (St-Gobain Performance Plastics) activated by the pressurized air from a diving tank, to collect surface (~15 cm) samples to characterize aerosols emissions (Schwier et al, 2015).…”