Biogeochemical observations during the winter-spring transition in East Antarctic sea ice: Evidence of iron and exopolysaccharide controls

• Published in: Marine Chemistry
• Main Authors: Van Der Merwe, P, Lannuzel, D, Mancuso Nichols, CA, Meiners, K, Heil, P, Norman, L, Thomas, DN, Bowie, AR
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science Bv 2009
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Antarctic; Austral; Antarc*; Sea ice
• Online Access: https://doi.org/10.1016/j.marchem.2009.08.001; http://ecite.utas.edu.au/62463

This paper documents the spatial distribution and concentration of exopolysaccharides at 9 discrete sea icesites, consisting of first year sea ice, and relates this information to physical (ice temperature, texture) andbiogeochemical (oxygen stable isotopic composition of the ice, salinity, macronutrients, dissolved iron,particulate organic carbon, dissolved organic carbon and Chlorophyll a) variables. The sampling was carriedout over a transition from austral winter to early spring conditions as part of the Sea Ice Physics andEcosystems eXperiment (SIPEX), during September/October 2007 in the 110130 E region off EastAntarctica. Exopolysaccharide concentrations in sea ice varied by 3 orders of magnitude from 2.8 to 2690 gxanthan equivalent (xeq.) l−1; basal ice mean 493 g xeq. l−1. Exopolysaccharides correlated significantlywith particulate organic carbon and Chlorophyll a but not with dissolved iron, dissolved organic carbon ormacronutrient data, indicating that exopolysaccharides are most likely produced in situ by autotrophic seaice biota, superimposed over fossil organics. We observed increased exopolysaccharide per unit biomass inthe colder surface to intermediate ice at three stations, supporting the theory that exopolysaccharides maybe used as a cryoprotectant. Mean bulk ice dissolved iron (depth integrated) across all ice cores was 2.37 nM(range 0.23 to 14.4 nM). Sea ice dissolved iron concentration was always elevated relative to seawater.Apparent dissolved iron and estimates of cellular carbon to iron ratios suggest that the sea ice microbial biotawas not limited by dissolved iron but may have been by NO2+NO3 or Si(OH)4. Conversely, under iceseawater algal communities may have been limited by dissolved iron and/or light and grazing at the time ofsampling. We observed a significant inverse correlation between dissolved Fe and Chlorophyll a in the basallayers of the ice, most likely indicating the active drawdown of dissolved Fe by the sea ice biota, combinedwith some fraction lost to the water column or converted to the particulate fraction.