The biogenic composition of the sea-surface microlayer in response to a changing environment
The sea-surface microlayer (SML) is the oceanic uppermost boundary in contact to the atmosphere, a sort of biofilm matrix where microorganisms and organic material largely contribute to its physical and chemical structure. By accumulating organic material, this surface film damps capillary waves and...
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| Format: | Thesis |
| Language: | English |
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2013
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| Online Access: | https://oceanrep.geomar.de/id/eprint/22635/ https://oceanrep.geomar.de/id/eprint/22635/1/Diss.%202013%20Galgani,L.pdf |
| Summary: | The sea-surface microlayer (SML) is the oceanic uppermost boundary in contact to the atmosphere, a sort of biofilm matrix where microorganisms and organic material largely contribute to its physical and chemical structure. By accumulating organic material, this surface film damps capillary waves and influences air-sea gas exchange across the ocean's surface. Furthermore, organic compounds in the SML contribute to organic enrichment of bursting bubbles at the sea-surface, creating droplets that later dry out in the air as organic marine aerosols. Given their extension, the oceans are the largest source of atmospheric aerosols susceptible to affect regional and global climate through radiation, precipitation, and cloud formation. At periods of high biological productivity, sea-spray droplets are largely constituted of water insoluble organic particles, mainly as marine microgels, that may derive from the SML. Marine gels originate in the size-continuum aggregation of dissolved organic matter (DOM) precursors from the colloidal size (< 1 μm) that assemble to larger particles reaching several millimeters. Gels are hotspots for intense microbial activity, as they are rich in nutrients and act as a physical substrate for cells to grow upon. Microbial processes, like DOM exudation and degradation, contribute to the continuous recycling of this gelatinous material. The present thesis investigated how organic compounds and gel particles in the SML vary as a function of biological activity in the surface ocean impacted by anthropogenic climate change. The work has been articulated in three parts, comprising a laboratory study, a seagoing mesocosm experiment, and a sampling campaign to the Central Arctic. The first study conducted in the laboratory with the marine diatom Thalassiosira weissflogii highlighted the enhanced presence of proteinaceous marine gels in the SML, determined as results of solely phytoplankton and bacterial metabolism. While polysaccharidic marine gels could also form from dispersed colloidal ... |
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