Insights into ocean-to-atmosphere transfer of humic-like substances and bacteria
Sea spray aerosols (SSA) are one of the most abundant aerosols in the atmosphere and strongly influence clouds and climate. The impact of SSA on climate is driven by its chemical composition, in particular the composition of organic matter in SSA; however a full understanding of the factors that control the transfer of organic matter from seawater to SSA has remained elusive. Here we use a combination of fluorescence techniques to examine the chemical composition of seawater, the sea surface microlayer, and SSA in order to identify the factors that give rise to the appearance of species in SSA. Moreover, we use state-of-the-art aerosol generation techniques to study the temporal changes in seawater and isolated SSA over the course of phytoplankton bloom mesocosm experiments that mimic rapid changes in ocean biology and chemistry. In this dissertation, a unique SSA fluorescence signature was characterized and the contribution of marine bacteria to SSA fluorescence was explored. Additional experiments discussed in this dissertation examine the timing of transfer for different classes of molecules in seawater, such as protein-like and humic-like substances (HULIS), and factors that control transfer were identified for each molecular class. Further studies on the HULIS produced during phytoplankton blooms reveal the importance of bacterial enzymes on the sea-air transfer of HULIS. This dissertation also examines the reliability of fluorescence to determine HULIS relative concentration in the presence of aggregation processes. Finally, in this dissertation, a novel approach to study the metabolic activity of marine bacteria is presented and the transfer of metabolically active marine bacteria is discussed. The findings presented herein help to unravel the complex chemical and biological factors that control SSA composition in the real atmosphere.