Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

• Published in: Marine Chemistry
• Main Authors: Zhou, Jiayun, Delille, Bruno, Kaartokallio, Hermanni, Kattner, Gerhard, Kuosa, Harri, Tison, Jean-Louis, Autio, Riitta, Dieckmann, Gerhard S., Evers, Karl-Ulrich, Jorgensen, Linda, Kennedy, Hilary, Kotovitch, Marie, Luhtanen, Anne-Mari, Stedmon, Colin A., Thomas, David N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2014
• Subjects: Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; Sea ice
• Online Access: https://orbi.uliege.be/handle/2268/172470; https://orbi.uliege.be/bitstream/2268/172470/1/IntericeV_general%20paper_revision2.1_styleBD.pdf; https://doi.org/10.1016/j.marchem.2014.09.013

peer reviewed We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of -14 °C for 14 days after which ice decay was induced by increasing the air temperature to -1 °C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicate that there was a succession of 3 stages in the brine dynamics: forced-convection, followed by bottom convection during ice growth, and then brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the ...