REEFAL CORALLINE ALGAL BUILD-UPS WITHIN THE ARCTIC-CIRCLE - MORPHOLOGY AND SEDIMENTARY DYNAMICS UNDER EXTREME ENVIRONMENTAL SEASONALITY

Carbonate frameworks secreted by phototrophic organisms within the Arc tic Circle are not well documented. Underwater surveys of the inner-sh elf off Troms, northern Norway (70 degrees N), reveal extended fixed a lgal build-ups which are fringed by rhodolith belts affected by storms . Reefal growth by coralline algae under temperature and light regimes of extreme seasonality is made possible because of a decoupling of ca rbon fixation during summer and utilization of stored carbon during th e period of winter darkness. Although the annual growth of the framewo rk constructing algae is comparatively low, the annual carbonate produ ction rate is similar to subtropical-tropical counterparts because of a remarkably high standing stock. Early diagenetic alteration is restr icted to intraparticle cementation processes which start in vivo. Bioe rosional destruction is the dominant control on the preservation of hi gh latitude build-ups. Preservation of Holocene autochthonous corallin e algal biostromes is enhanced by rapid burial during storm events. Re deposition during storms is the most important process in forming a di stinct sedimentary facies zonation.