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 micrometers in diameter and by their rare aggregates. Distribution of the vivianite grains in the core is characterized by three maximal values (up to 2.7 grains per gram of dry bulk sediment), within the time interval of the last 4.1 kyr. Linear and flat shape of the aggregates indicates generation of vivianite at the sediment/water interface. It takes place in the reducing condition and sulfide sulfur deficit in the bottom water relative to bivalent iron. Structure of the vivianite grains varies from the cryptocrystalline porous to the fully crystalline dense one reflecting stages of the vivianite crystallization, likely after coagulation of the ferrous phosphate colloid formed due to the bacterial activity. Signs of vivianite microconcrections mentioned by some authors are not observed.