Geochemical and sedimentological considerations of a permanently anoxic fjord — Framvaren, south Norway

Abstract

Framvaren, a fjord in south Norway, is an example of extreme anoxia, due to the geomorphological features (sill depth ∼ 2 m, basin depth ∼ 180 m). The postglacial history of Framvaren is outlined emphasizing the preservation of environmental changes in the properties of the water and the sediments. High levels of hydrogen sulfide in the water (170–180 ml l −1 or 7–8 mM H 2S) dense populations of photosynthetic bacteria at the redox boundary (total number ∼ 3 × 10 6ml −1), metal-sulfide formation in the anoxic water (e.g. framboidal pyrite and zinc sulfide) and organic-rich bottom sediments with high metal content (e.g. > 1000 ppm Zn), are typical examples. The rate of sedimentation is estimated in three independent ways suggesting an average, annual flux of ∼ 100 g m −2 yr −1 in the central basin of Framvaren. Fluxes of organic matter and zinc to the sediments are calculated and compared with potential sources.