| Summary: | Despite widespread iron (Fe) limitation in the Southern Ocean, Antarctic coastlines are highly productive, supporting biodiverse ecosystems and atmospheric carbon sequestration. Iron is an essential micronutrient for cellular processes such as photosynthesis; therefore, its scarcity in surface waters is a key limitation on primary productivity. Seasonally variable sources of Fe to coastal waters include sediment resuspension, basal ice melt, dust deposition and sea-ice melt, as well as upwelling and vertical mixing of offshore deep waters. Early spring phytoplankton blooms rapidly deplete Fe, after which internal Fe recycling processes support productivity into late summer. Bacterial Fe remineralisation and pelagic recycling by marine animals are thought to influence the distribution of recycled Fe during this period. The chemical nature of Fe influences its bioavailability to microbial communities. For example, complexation by ligands increases Fe solubility in surface waters by reducing scavenging onto particles. However, little is known about the late summer distribution and bioavailability of Fe from different Antarctic coastal sources, which are expected to be impacted by climate change. This dissertation explores the bioavailability of coastal Fe sources and directly assesses distribution and complexation of Fe in a coastal Antarctic environment during late summer when recycling processes are thought to dominate. Chapter 2 assesses the bioavailability of Fe from seven different coastal Antarctic sources. These include two geological sources: Antarctic continental dust and shelf sediments, and five biological sources: sea ice (pack ice), and faecal material from four marine animals (Antarctic krill, baleen whales, penguins, and seals). The concentration of labile Fe, solubility of dissolved Fe and complexation by Fe-binding ligands were measured as an indicator of Fe bioavailability. Poorly soluble Fe (<3%) from physical sources was subject to scavenging by particles in seawater. Whereas up to 30% of ...
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