Organic carbon and microbial biomass in a raised beach deposit under terrestrial vegetation in the High Arctic, Ny-Ålesund, Svalbard

Raised beach deposits are widespread on the north-western coast of Spitsbergen, Svalbard. To elucidate the importance of these deposits in an ecosystem carbon cycle, we measured the concentrations of organic carbon and adenosine 5-triphosphate (ATP; an index of living microbial biomass) in a raised beach deposit found under terrestrial vegetation in Ny-Ålesund. A shell in the deposit found at a depth of ca. 20 cm below the ground surface had a (not calibrated) ¹⁴C age of 11080 ± 140 yr BP, whereas soil organic carbon in the same deposit showed an older ¹⁴C age (22380 ± 90 yr BP). Organic carbon concentration in the layer of 20-40 cm belowground was about 1-2%, which was comparable to those in shallower mineral soil layers. Results of ATP analyses suggested that low but non-negligible amounts of microorganisms existed in the deposit. The proportion of biomass carbon to soil organic carbon tended to decrease with increasing depth, suggesting that organic carbon in the deep layer was less available to microorganisms than that in the shallow layers.