Modern nearshore cold-temperate calcareous sediments in the Troms district, Northern Norway

Abstract

ABSTRACT During the past 6400 years rocky coastal platforms and outer fjord troughs in the Troms District, northern Norway (70°N) became sites of considerable production and deposition of skeletal carbonate in a cold-temperate environment under Arctic solar radiation conditions. Because of poleward heat transfer by the Norwegian Current along the eastern margin of the North Atlantic Ocean, the cold-temperate marine climate persists beyond the Arctic Circle. In the shallow subtidal zone, carbonate generation is confined to benthic macroalgal ecosystems. Along the wave-exposed margins of the coastal platforms, kelp forests provide habitats for numerous carbonate-secreting organisms such as barnacles, echinoids, and bivalves. Kelp with attached calcareous organisms is involved in many redistributional processes such as rafting and phylloid drift. Reef growth of coralline algae, together with maerl deposits and rhodolith pavements, dominate in wave-sheltered platform areas. This windward-leeward zonation of carbonate production along the rocky coasts reflects specific properties of coralline algae versus kelp to withstand physical disturbances of episodic storms. Carbonate sediment in gullies or outer fjord troughs consists of molluscs, bryozoans, benthic foraminifers, and verrucid barnacles. Terrigenous sediment loads delivered as spring meltwater discharge is trapped in the inner fjord troughs. Hydrodynamic concentration of calcareous skeletons is fostered by a complex topography that offers numerous sediment-trapping areas along the rocky coastline and outer fjord troughs. Physiological adaptation of coralline algae to cope with extreme seasonality in solar radiation is a prerequisite for the formation of coralline algal reefs beyond the Arctic Circle, which have carbonate production rates near those of subtropical coralline algal grounds.