27 research outputs found
Selective incorporation of dissolved organic matter (DOM) during sea ice formation
This study investigated the incorporation of DOM from seawater into >2 day-old sea ice in tanks filled with seawater alone or amended with DOM extracted from the microalga, Chlorella vulgaris. Optical properties, including chromophoric DOM (CDOM) absorption and fluorescence, as well as concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved carbohydrates (dCHOs) and dissolved uronic acids (dUAs) were measured. Enrichment factors (EFs), calculated from salinity-normalized concentrations of DOM in bulk ice, brine and frost flowers relative to under-ice water, were generally >1. The enrichment factors varied for different DOM fractions: EFs were the lowest for humic-like DOM (1.0–1.39) and highest for amino acid-like DOM (1.10–3.94). Enrichment was generally highest in frost
flowers with there being less enrichment in bulk ice and brine. Size exclusion chromatography indicated that there was a shift towards smaller molecules in the molecular size distribution of DOM in the samples collected from newly formed ice compared to seawater. Spectral slope coefficients did not reveal any consistent differences between seawater and ice samples. We conclude that DOM is incorporated to sea ice relatively more than inorganic solutes during initial formation of sea ice and the degree of the enrichment depends on the chemical composition of DO
Influence of Australian desert dust on marine iron chemistry and bioavailability to phytoplankton
info:eu-repo/semantics/nonPublishe
Quantification of ikaite in Antarctic sea ice
Calcium carbonate precipitation in sea ice is thought to potentially drive significant CO2 uptake
by the ocean. However, little is known about the quantitative spatial and temporal distribution of CaCO3
within sea ice, although it is hypothesized that high quantities of dissolved organic matter and/or phosphate
(common in sea ice) may inhibit its formation. In this quantitative study of hydrous calcium carbonate as
ikaite, sea ice cores and brine samples were collected from pack and land fast sea ice between September
and December 2007 during two expeditions, one in the East Antarctic sector and the other off Terre Ade´lie.
Samples were analysed for CaCO3, salinity, dissolved organic carbon/nitrogen, inorganic phosphate, and
total alkalinity. No relationship between these parameters and CaCO3 precipitation was evident. Ikaite was
found mostly in the uppermost layers of sea ice with maximum concentrations of up to 126 mg ikaite per
litre melted sea ice being measured, although both the temporal and horizontal spatial distributions of ikaite
were highly heterogeneous. The precipitate was also found in the snow on top of the sea ice at some of the
sampling locations
Dissolved extracellular polymeric substance (dEPS) dynamics and bacterial growth during sea ice formation in an ice tank study
Iron Biogeochemistry in Aquatic Systems: From Source to Bioavailability
Iron (Fe) is an essential trace element for several key metabolic processes in phytoplankton; however Fe is present in low concentration in many aquatic systems including vast oceanic regions and large lakes. In these systems, Fe can limit the growth of phytoplankton and atmospheric carbon dioxide biological fixation. Indeed Fe limitation exerts a global impact on the carbon cycle and the imprint of aquatic systems on our climate. In order to understand how aquatic systems function and increase our ability to predict their response to changing conditions, it is therefore paramount to understand when and how Fe controls operate. This review presents the complex relationship between Fe chemistry and the biology of surface waters to highlight the parameters defining the forms of Fe that are accessible for phytoplankton growth (or bioavailable). Particular attention is given to the identification of Fe sources and Fe organic complexation as these, in conjunction with biological recycling and remineralisation, mostly control Fe residence time, chemistry and bioavailability