Data from: Last Glacial Maximum environmental conditions at Andøya, northern Norway; evidence for a northern ice-edge ecological "hotspot"

Andøya on the NW coast of Norway is a key site for understanding the Last Glacial
Maximum (LGM) in northern Europe. Controversy has arisen concerning the local conditions,
especially about the timing and extent of local glacial cover, maximum July temperatures and
whether pine and/or spruce could have grown there. We reviewed all existing data and add
newly analysed ancient sedimentary DNA, pollen, macrofossils, geochemistry and stable
isotopes from three lake sediment cores from Øvre Æråsvatnet. A total of 23 new dates and
age-depth modelling suggests the lake has been ice-free since GI2 (<22.8 k cal. BP) and
possibly GS3 (<27.4 k cal. BP). Pinus and Picea sedimentary ancient DNA (sedaDNA) was
found in all three cores but at such low frequencies that it could not be distinguished from
background contamination. LGM samples have an exceptionally high organic matter content,
with isotopic values indicating that carbon and nitrogen derives from a marine source. Along
with finds of bones of the little auk (Alle alle), this indicates that the lake received guano from
an adjacent bird colony. DNA, pollen and macrofossil assemblages were dominated by
Poaceae, Brassicaceae and Papaver, but scattered occurrence of species currently restricted to
the Low Arctic Tundra Zone (July temperature of 8-9°C) such as Apiaceae (DNA, 8-9°C),
and Alchemilla alpina (macrofossil, 8-9°C) were also recorded. The review showed 94
recorded vascular plant taxa, of which 38% have a northern limit in Shrub Tundra or more
southern vegetation zones. This unusual assemblage likely stems from a combination of
proximity to ice-free water in summer, geographical isolation linked with stochastic long-
distance dispersal events, and the presence of bird-fertilized habitats. The environmental
reconstruction based on all records from the area does not preclude local growth of tree
species, as the local climate combined with high nutrient input may have led to periodically
suitable environmental 'hotspot' conditions.