Spectral densities of annual runoff of main Arctic rivers.
Period oscillation is determined as T_k = 48/k [years], where k is the conditional Frequency.

( After Alekseyev G. V et. al., River outflow variability. Technical Report on Task 2, Grant INTAS 97-1277: Detection and Modeling of Greenhouse Warming in the Arctic and sub-Arctic. Arctic and Antarctic Research Institute, St. Petersburg, 1999.)