No abstract

No abstract

The physical properties of Arctic sea ice determine its habitability. Whether ice-dwelling organisms can change those properties has rarely been addressed. Following discovery that sea ice contains an abundance of gelatinous extracellular polymeric substances (EPS), we examined the effects of algal EPS on the microstructure and salt retention of ice grown from saline solutions containing EPS from a culture of the sea-ice diatom, Melosira arctica. We also experimented with xanthan gum and with EPS from a culture of the cold-adapted bacterium Colwellia psychrerythraea strain 34H. Quantitative microscopic analyses of the artificial ice containing Melosira EPS revealed convoluted ice-pore morphologies of high fractal dimension, mimicking features found in EPS-rich coastal sea ice, whereas EPS-free (control) ice featured much simpler pore geometries. A heat-sensitive glycoprotein fraction of Melosira EPS accounted for complex pore morphologies. Although all tested forms of EPS increased bulk ice salinity (by 11-59%) above the controls, ice containing native Melosira EPS retained the most salt. EPS effects on ice and pore microstructure improve sea ice habitability, survivability, and potential for increased primary productivity, even as they may alter the persistence and biogeochemical imprint of sea ice on the surface ocean in a warming climate.ice algae | permeability | polysaccharides | saline ice O ver the past few decades, the extent and thickness of Arctic sea ice have undergone significant climate-driven reductions that show no abatement (1-3). Current polar ecosystems depend on sea ice as a platform for foraging and reproduction by marine organisms and as a porous matrix that supports extensive blooms of ice algae. In the Arctic, these blooms account for a seasonally early and dominant fraction of total spring primary production (4). With continued reductions in areal extent of summer sea ice, however, phytoplankton activity in open waters is expected to dominate total primary production (5), leading to shifts away from ecosystems supported by fluxes of ice-algal material to the seafloor (6) toward pelagic ecosystems characteristic of lower latitudes (7). Predictions of reduced ice-algal production, however, do not consider the possibility that changes to sea ice microstructure and physical properties may stimulate primary productivity in the remaining ice.Here we reframe the question of how large-scale losses of Arctic sea ice will impact ecosystems and ask instead whether organisms-in particular sea-ice algae-have evolved means to alter ice physical properties to their benefit, mitigating impacts of climate change. The mechanism we consider derives from the biological production of extracellular polysaccharide substances (EPS)-organic materials of high surface area and complex behavior in aqueous solution (8)-observed microscopically in the brine inclusions of sea ice, where they are thought to function as cryoprotectants (9) and osmoprotectants (10). Do these substances also alter the microstructure of the...

No abstract