Funding for this research was provided by:
Russian Foundation for Basic Research (16-05-00979)
Russian and German ministries for science and education (Changing Arctic Transpolar System)
Received: 1 August 2017
Accepted: 4 January 2018
First Online: 23 January 2018
Compliance with ethical standards
: On behalf of all authors, the corresponding author states that there is no conflict of interest.