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...

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ABSTRACT. Although shorefast sea ice forms a platform that facilitates travel, camping, and hunting by Iñupiat subsistence hunters and fishers in the western Arctic, the nearshore sea-ice zone remains an unforgiving and dynamic environment. Traditional hunters constantly hone site-specific experiences and skills with which to optimize the reward-to-risk ratio inherent in operating from this coastal ice. Nearshore ice conditions nevertheless can change suddenly, endangering even the most experienced subsistence hunters. This study examines two (of several) 20th-century events, 40 years apart, in which shorefast ice failed, threatening Iñupiat whale hunters with loss of confidence, livelihood, and life. These events differed in character. In one event, the shorefast ice was "crushed" by moving ice floes. In the other, the shorefast ice broke free of land. Our examination focuses on the relationship of subsistence hunters to the ice, the environmental causes of ice failures, the evolving technology for predicting ice behavior, and the longer-term implications of global change for this system. The complexity of geophysical processes underlying coastal ice behavior makes ice failures unpredictable. Thus, hunters must assume and manage risk. The variable and uncertain environment to which whale hunters are accustomed has produced an inherent flexibility that has helped them adapt to new conditions and will continue to do so in the future.Key words: Iñupiat, sea ice, safety, breakup, calving, shorefast ice, hunting, technology, whaling, Barrow RÉSUMÉ. Bien que la banquise côtière constitue une plate-forme qui permet aux Iñupiat de l'Arctique de l'Ouest de se déplacer et de camper lorsqu'ils pratiquent la chasse et la pêche de subsistance, la zone de banquise proche du littoral reste un milieu dynamique qui ne pardonne pas. Les chasseurs traditionnels améliorent constamment les habiletés et l'expérience reliées à des sites particuliers, qui leur permettent d'optimiser le rapport récompense-risque inhérent au fait de travailler depuis la glace côtière. Les conditions de cette dernière peuvent toutefois changer brusquement, mettant en danger même les chasseurs de subsistance les plus chevronnés. Cette étude se penche sur deux (parmi plusieurs) épisodes survenus au XX e siècle, à 40 ans d'écart, durant lesquels la banquise côtière s'est rompue, ébranlant la confiance des baleiniers Iñupiat et menaçant leur moyen de subsistance ainsi que leur vie. Ces événements étaient de nature différente. Dans l'un, la glace côtière avait été «écrasée» par des floes en dérive. Dans l'autre, la banquise côtière s'était détachée de la terre ferme. Notre étude se concentre sur le rapport entre les chasseurs de subsistance et la glace, les causes environnementales de la fragilisation de la glace, la technologie mise au point actuellement qui permettrait de prédire le comportement de la glace, et les implications à long terme du changement climatique pour ce système. La complexité des processus géophysiques sous-jacents au comportement de la ...

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