NEW CALCITE DISSOLUTION FEATURES OBSERVED IN TUNDRA SOILS, SPITSBERGEN

Carbonate minerals are important components of several geochemical cycles, including carbon cycle. Field observations of calcite weathering in environments experiencing active climate change can provide important information about rates and modes of modifications of these cycles. This study presents the results of calcite chemical weathering in tundra soils. The studied samples have been buried in the arctic soil of Spitsbergen. The study uses a complimentary combination of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) imaging. The samples of freshly cleaved calcite were placed in the soil in vials with openings allowing for chemical reactions between the buried samples and gases and water. The samples were buried at a distance of 10 meters from the shore line of the Greenland Sea. The chemical reactions on calcite surfaces were affected by acidic soil conditions (ph=4.5), sea aerosols, the presence of a snow cover over a period of 9 months per year, and relatively aggressive waters characterized by a low amount of total dissolved solids. Three samples that were buried in the arctic tundra soil were subsequently recovered after one, three, and four years respectively. Recovered calcite samples are characterized by three types of surface features. The surface of the sample recovered after one year is covered in approximately 50% by circular depressions about 600 nanometers deep. These depressions were also observed in a tundra soil environment observed in the Rocky Mountains, USA at an elevation of about 3400 m amsl. It is believed that they are related to evaporation of highly acidic droplets in soil environment. Two other surface features, dissolution of channels and dissolution along rombohedral crystals are related to crystallographic directions. It is important to notice that overall typical dissolution features known from laboratory experiments, such as etch pits are not very common and their distribution is heterogeneous. This suggests that field dissolution processes are not represented well by laboratory conditions. Similar dissolution patterns along rombohedral cleavage were identified before in calcite short-term reactions with EDTA solutions that are often used to simulate reactions with organic soil matter. Longer-term reactions with EDTA produce rather flat surfaces.