Biogeochemistry of selenium in the oceans of the southern hemisphere

• Main Author: Wake, BD
• Format: Thesis
• Language: English
• Published: 2010
• Subjects: Selenium; Biogeochemistry; Chemical oceanography; Austral; Antarc*; Antarctica
• Online Access: https://eprints.utas.edu.au/22262/; https://eprints.utas.edu.au/22262/1/whole_WakeBronwynDavina2010_thesis.pdf

Selenium (Se) is a key micronutrient for marine primary productivity in the remote ocean. The element is known to be essential for phytoplankton species growth, but there is limited information on its role and physiological function. This study is the first to investigate basin-scale distributions, speciation and biological requirements of Se for phytoplankton in the various water masses of the Southern Hemisphere, ranging from the subtropical to the polar oceans. The thesis describes the development of a new shipboard method based on hydride generation with cryogenic trapping and atomic fluorescence detection for the determination of Se species in seawater. A detection limit of \(5 pmol\) `l^-1` `Se` in a 10-ml sample was achieved, with precision better than 3.5% for Se(IV) standards (\(0.3-12.7 nmol\) `l^-1`). Accuracy was determined by recovery studies on natural samples and certified reference seawater. An ocean transect from Australia to Antarctica along the meridional CLIV AR I9S line (approximately 115°E) was completed in the austral summer 2004/2005. Water column samples were collected in all ocean provinces, with increased sampling in the mixed layer and frontal zones. Results show surface Se(IV) concentrations increasing towards the south. The Se data has been interpreted using ancillary chemical and biological data obtained from the transect. Laboratory-based cultures were grown to investigate the effect of varying Se concentrations on the productivity and cell health of two temperate and four polar oceanic phytoplankton species. The coccolithophore, Emiliania huxleyi, required Se obligately for growth, whereas no effect was observed with the cyanobacterium, Synechococcus sp. The effect of Se additions on cell photosynthetic parameters was reflected by an increase in pigment concentrations for three of the polar diatoms. The absolute biological requirement for Se was thus demonstrated in laboratory cultures, with varying requirements among different species.