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 Arctic Circle are not well documented. Underwater surveys of the inner-shelf off Troms, northern Norway (70 degrees N), reveal extended fixed algal 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 carbon fixation during summer and utilization of stored carbon during the period of winter darkness. Although the annual growth of the framework constructing algae is comparatively low, the annual carbonate production rate is similar to subtropical-tropical counterparts because of a remarkably high standing stock. Early diagenetic alteration is restricted to intraparticle cementation processes which start in vivo. Bioerosional destruction is the dominant control on the preservation of high latitude build-ups. Preservation of Holocene autochthonous coralline algal biostromes is enhanced by rapid burial during storm events. Redeposition during storms is the most important process in forming a distinct sedimentary facies zonation.