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Edges: cryosphere, seafloor and shores, and human footprints

2026
Albert Calbet

Summary

This review paper explains that ocean life depends heavily on "edges" — sharp boundaries like ice-water interfaces, coastlines, and the zones where pollution meets marine ecosystems — where conditions change quickly and organisms are most vulnerable. Human-made pollutants like microplastics, PFAS "forever chemicals," and industrial runoff are creating new dangerous edges that fish and other sea creatures must navigate to survive, and since these same pollutants end up in seafood, this matters for what ends up on our plates. As climate change shifts where and when these edges occur, it could disrupt the ocean food web that

The ocean’s most decisive habitats are thin. Along sharp gradients and interfaces—where temperature, salinity, density, roughness, chemistry, and velocity change over short distances or brief intervals—organisms find the highest returns and the highest risks. This chapter treats edge-worlds in one integrative frame because they share a common geometry and logic: polar ice and its brine-channeled interior with the mobile under-ice ceiling and the shifting marginal ice zone; the coastal and benthic boundary where porous sands breathe with waves, turbidity maxima shuttle flocs and larvae, groundwater seeps draw halos on the seabed, and shelf breaks, canyons, seamounts, vents, and seeps compress prey and mint sticky carbon; and the urban and industrial sea where thermal ribbons, dense brines, oxidants, nutrients, hydrocarbons, metals, plasticizers, PFAS, surfactants, microplastics, tire particles, and noise manufacture new edges that embryos, larvae, and gills must cross each day. Climate change shifts the frequency, intensity, and timing of the same edges rather than inventing new rules, moving thresholds for viscosity, buoyancy, saturation, redox, and turbulence that organisms already use as cues. Read correctly, edges are not merely pretty lines on satellite maps; they are the operating geometry of the ocean’s surface, interior, and floor.

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