Southern Ocean phytoplankton silica uptake: implications for leakage and carbon export

Abstract

The silicic acid cycle is closely linked to the carbon cycle in oceans as diatoms, a dominant, siliceous phytoplankton in the Southern Ocean (SO., are estimated to be responsible for the removal of approximately 55% of the total organic carbon in modern oceans. The incorporation of silicic acid into the diatom cell wall structure, carbon export, productivity and biogenic silica distribution are reported in this paper through incubation experiments and transect data addressing pitfalls of the Silicic Acid Leakage Hypothesis. Upon iron (Fe. fertilization, the potential for the community to utilize less silicic acid from the water column is evaluated. The study spans a winter and three summer cruises, including the Atlantic and Indian Sectors of the SO. Biogenic silica is coupled with ancillary trace metal, macronutrient, particulate organic carbon (POC., Chlorophyll a and community composition data. Incubation experiments within the community illustrate a noticeable increase in biogenic silica under high iron and light regimes, whilst transect data reiterate these limitations. Results suggest an increase in productivity across all oceanic zones. Scanning Electron Microscopy imaging indicates that upon Fe fertilization, changes in the thickness of the diatom cell wall are species-specific. To conclude, Fe addition drastically increases diatom production with certain species displaying a thinning of the cell wall marking potential for excess silicic acid in the water column. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.