Granulated Vivianite in the Cambridge Strait, Franz Josef Land (Barents Sea)

Finding of vivianite is first described in a sediment core raised from the Cambridge Strait, western Franz Josef Land. The vivianite is represented by similar spherules mainly of 200–400 µm in diameter and their rare aggregates. Distribution of vivianite grains in the core is characterized by three maxima (up to 2.7 grains/g of dry bulk sediment) within the time interval of the last 4.1 ka. Linear and flat shapes of the aggregates indicate the generation of vivianite at the sediment–water interface. It takes place in the reduced condition at sulfide sulfur deficit relative to divalent iron in the bottom water. The structure of vivianite grains varies from the cryptocrystalline porous to the fully crystalline dense variety, reflecting stages of the vivianite crystallization, likely after coagulation of the ferrous phosphate colloid formed due to the bacterial activity. Signs of vivianite microconcretions mentioned by some authors are not observed.