Aslam SN, Underwood GJC, Kaartokallio H, Norman L, Autio R, Fischer M, Kuosa H, Dieckmann GS, Thomas DN
Sea ice, Extracellular polymeric substances, Frost flowers, Bacteria, Dissolved carbohydrate, DOM, EPS, mesocosm, HSVA test basin, Hamburg, Germany, 1.2 m3
Extracellular polymeric substances (EPS) areknown to help microorganisms to survive under extremeconditions in sea ice. High concentrations of EPS arereported in sea ice from both poles; however, productionand dynamics of EPS during sea ice formation have beenlittle studied to date. This investigation followed the productionand partitioning of existing and newly formed dissolvedorganic matter (DOM) including dissolvedcarbohydrates (dCHO), dissolved uronic acids (dUA) anddissolved EPS (dEPS), along with bacterial abundancesduring early stages of ice formation. Sea ice was formedfrom North Sea water with (A) ambient DOM (NSW) and(B) with additional algal-derived DOM (ADOM) in a 6dexperiment in replicated mesocosms. In ADOM seawater,total bacterial numbers (TBN) increased throughout theexperiment, whereas bacterial growth occurred for 5d onlyin the NSW seawater. TBN progressively decreased withindeveloping sea ice but with a 2-fold greater decline in NSWcompared to ADOM ice. There were signiWcant increasesin the concentrations of dCHO in ice. Percentage contributionof dEPS was highest (63%) in the colder, uppermostparts in ADOM ice suggesting the development of a coldadaptedcommunity, producing dEPS possibly for cryoprotectionand/or protection from high salinity brines. Weconclude that in the early stages of ice formation, allochthonousorganic matter was incorporated from parent seawaterinto sea ice and that once ice formation had established,there were signiWcant changes in the concentrations andcomposition of dissolved organic carbon pool, resultingmainly from the production of autochthonous DOM by thebacteria.