This study examines the distribution and seasonal evolution of hydrographic, hydrodynamic, and nepheloid layers in Ushuaia Bay and the submerged glacial valley that connects it to the Beagle Channel. The hydrographic structure is highly seasonal, with a total mixing of the water column in winter and the appearance of a pycnocline between 50 and 70 m deep from spring to late autumn, mainly due to desalination. A counter-clockwise current sweeps the entire bay regardless of the season or phase of the tide. This current is at its maximum in the surface layer, allowing the rapid renewal of the bay’s waters, while deep currents are weak and imply a slow renewal of the valley’s waters. Turbid and oxygen-depleted structures are observed in summer in the valley. The combination of seasonal stratification, high organic matter inputs from planktonic production, oxygen consumption for remineralization, and sluggish circulation results in a decrease in near-bottom oxygen concentration in the glacial valley at the end of the stratified season, before mixing and re-oxygenation of the water column during the southern winter. The possible impact of dissolved oxygen depletion in the bottom waters of the valley on benthic organisms, like crustaceans, is discussed.

The objective of this work was to identify the species of acid-thermophilic cyanobacteria which, together with the waters, microalgae and mud, are important thermal resources used for therapeutic purposes in the Copahue Thermal Complex. The work presents descriptions, comments, and illustrations of the 11 identified species belonging to nine genera: Chroococcidiopsis, Chroococcus, Kamptonema, Komvophoron, Leptolyngbya, Mastigocladus, Oscillatoria, Phormidium and Spirulina, collected in ten sampling sites. Five species: Chroococcus membraninus, Chroococcidiopsis thermalis, Spirulina gracilis, Phormidium thermobium, and Komvophoron jovis, are cited for the first time for Argentina. In addition, four species were isolated and maintained in unialgal culture: Chroococcus membraninus, Chroococcidiopsis thermalis, Kamptonema animale and Mastigocladus laminosus. M. laminosus was the most frequently encountered species of the area, since it was found in eight of the ten sites. The Laguna Los Callos was the most diverse site, with the largest number of species, eight in total. All the species of cyanobacteria studied in the present work are used, either through the direct application of the mats or through the use of their active components in water, and mud.

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