Bio-optical characteristics of the snow, ice, and water column of a perennially ice-covered lake in the High Arctic

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Abstract:

Lake A is a meromictic, perennially ice-covered lake located at the northern limit of North America (latitude 83°N, Ellesmere Island, Canada). In early June 1999, only 0.45% of incident photosynthetically available radiation (PAR) was transmitted through its 2-m ice and 0.5-m snow cover. Removal of snow from 12 m2 increased PAR under the ice by a factor of 13 and biologically effective ultraviolet radiation (UVR) by a factor of 16 (from 0.4% to 6.3% of incident). The diffuse attenuation coefficient (Kd) for UVR was substantially lower in the ice than in the underlying freshwater (e.g., 50% lower at 320 nm), indicating the exclusion of chromophoric dissolved organic matter (CDOM) during freeze-up or the subsequent degradation of CDOM retained in the ice. Peak phytoplankton concentrations occurred immediately under the ice, and a broad maximum of photosynthetic sulfur bacteria and associated sulfur particles was observed over the depth interval 20–45 m at <0.005% of incident PAR. Climate-induced changes in the overlying snow and ice have the potential to cause major habitat disruption (UV exposure, PAR, temperature, mixing regime) for these stratified, extreme-shade communities.

Le lac A est un lac méromictique couvert de glace en permanence et situé à la limite boréale du continent nord-américain (latitude 83°N, île d'Ellesmere, Canada). Au début de juin 1999, seulement 0,45 % de la radiation incidente disponible pour la photosynthèse (PAR) pénétrait la couche de 2 m de glace recouverte de 0,5 m de neige. Le retrait de la neige sur une surface de 12 m2 a augmenté la PAR d'un facteur de 13 et la radiation ultraviolette (UVR) à effets biologiques, d'un facteur de 16 (de 0,4 % à 6,3 % de la radiation incidente). Le coefficient d'atténuation (Kd) de l'UVR était considérablement moins élevé dans la glace que dans l'eau douce sous-jacente (e.g. 50 % plus faible à 320 nm), ce qui indique une exclusion de la matière organique dissoute colorée (CDOM) lors du gel ou la dégradation subséquente de la CDOM retenue dans la glace. Les concentrations maximales de phytoplancton se trouvaient juste sous la glace et la densité maximale des bactéries sulfureuses photosynthétiques et des particules de soufre associées s'étalait dans l'intervalle des profondeurs de 20–45 m, à moins de 0,005 % de la PAR incidente. Les changements dans la couverture de neige et de glace générés par le climat peuvent potentiellement causer des modifications majeures de l'habitat (exposition à l'UV, PAR, température, régime de brassage) dans ces communautés stratifiées acclimatées à de faibles intensités lumineuses.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2001

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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