A paradox is commonly observed in productive sea ice in which an accumulation in the macro-nutrients nitrate and phosphate coincides with an accumulation of autotrophic biomass. This paradox requires a new conceptual understanding of the biogeochemical processes operating in sea ice. In this study, we investigate this paradox using three time series in Antarctic landfast sea ice, in which massive algal blooms are reported (with particulate organic carbon concentrations up to 2,600 µmol L–1) and bulk nutrient concentrations exceed seawater values up to 3 times for nitrate and up to 19 times for phosphate. High-resolution sampling of the bottom 10 cm of the cores shows that high biomass concentrations coexist with high concentrations of nutrients at the subcentimeter scale. Applying a nutrient-phytoplankton-zooplankton-detritus model approach to this sea-ice system, we propose the presence of a microbial biofilm as a working hypothesis to resolve this paradox. By creating microenvironments with distinct biogeochemical dynamics, as well as favoring nutrient adsorption onto embedded decaying organic matter, a biofilm allows the accumulation of remineralization products (nutrients) in proximity to the sympagic (ice-associated) community. In addition to modifying the intrinsic physicochemical properties of the sea ice and providing a substrate for sympagic community attachment, the biofilm is suggested to play a key role in the flux of matter and energy in this environment.
In seawater, trace metals occur in many forms: free ion, labile and non-labile complex, colloid, associated with particles, but only free ions and very labile metal complexes can cross the phytoplankton membrane and be assimilated. In this paper we review the most appropriate determination methods for those metal species, addressing particularly in situ speciation and preconcentration. Focus is on DGT-ICPMS, which is a technique that meets these criteria very well. In coastal environments, DGT probes are widely used for metal pollution monitoring, but in open ocean a carrier such as a glider, is required. In open ocean organic metal complexation has been studied using DGT-ICPMS and electrochemical methods. The use of DGTs with different diffusion domain thicknesses provides information to quantify labilities and dissociation rates of metal complex pools. Labilities of metal complexes in coastal waters appeared to be higher than in open sea.
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