Hidden biofilms in a far northern lake and implications for the changing Arctic

The high Arctic sampling site and biofilms. a Location of Ward Hunt Lake (red star) relative to the North Pole (white cross); the base map is the International Bathymetric Chart of the Arctic Ocean (IBCAO) of the Intergovernmental Oceanographic Commission (IOC), version 3.0 released in the public domain on 8 June 2012;20 b Ward Hunt Lake in mid-July 2015 showing the littoral open water zone (moat) and multi-year ice over the deeper waters of the lake; c Shallow biofilm over the rocks in the moat zone; d Sample of the deep biofilm in a mini-Glew sediment core (38？mm diameter) from 10？m depth; and e Schematic diagram of the biofilm color zonation (description in Supplementary Results