The characteristics of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in Antarctic sea ice

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Norman, L, Thomas, DN, Stedmon, CA, Granskog, MA, Papadimitriou, S, Krapp, RH, Meiners, KM, Lannuzel, D, Van Der Merwe, P, Dieckmann, GS
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Science Ltd 2011
• Subjects: Environmental Sciences; Ecological applications; Ecosystem function; Antarctic; Antarc*; Sea ice
• Online Access: https://doi.org/10.1016/j.dsr2.2010.10.030; http://ecite.utas.edu.au/72229

An investigation of coloured dissolved organic matter (CDOM) and its relationships to physical andbiogeochemical parameters in Antarctic sea ice and oceanic water have indicated that ice melt may bothalter the spectral characteristics of CDOM in Antarctic surface waters and serve as a likely source of freshautochthonous CDOM and labile DOC. Samples were collected from melted bulk sea ice, sea ice brines,surface gap layer waters, and seawater during three expeditions: one during the spring to summer andtwo during the winter to spring transition period. Variability in both physical (temperature and salinity)and biogeochemical parameters (dissolved and particulate organic carbon and nitrogen, as well aschlorophyll a) was observed during and between studies, but CDOMabsorption coefficients measured at375 nm (a375) did not differ significantly. Distinct peaked absorption spectra were consistently observedfor bulk ice, brine, and gap water, but were absent in the seawater samples. Correlation with the measuredphysical and biogeochemical parameters could not resolve the source of these peaks, but the shouldersand peaks observed between 260 and 280 nmand between 320 to 330 nmrespectively, particularly in thesamples taken from high light-exposed gap layer environment, suggest a possible link to aromatic andmycosporine-like amino acids. Sea ice CDOM susceptibility to photo-bleaching was demonstrated in anin situ 120 hour exposure, during which we observed a loss in CDOM absorption of 53% at 280 nm, 58% at330 nm, and 30% at 375 nm. No overall coincidental loss of DOC or DON was measured during theexperimental period. A relationship between the spectral slope (S) and carbon-specific absorption (an375)indicated that the characteristics of CDOM can be described by the mixing of two broad end-members;and aged material, present in brine and seawater samples characterised by high S values and low an375; anda fresh material, due to elevated in situ production, present in the bulk ice samples characterised by low Sand high an375. ...