Data from: Ice-cover is the principal driver of ecological change in High Arctic lakes and ponds

Recent climate change has been especially pronounced in the High Arctic,
however, the responses of aquatic biota, such as diatoms, can be modified
by site-specific environmental characteristics. To assess if
climate-mediated ice cover changes affect the diatom response to climate,
we used paleolimnological techniques to examine shifts in diatom
assemblages from ten High Arctic lakes and ponds from Ellesmere Island and
nearby Pim Island (Nunavut, Canada). The sites were divided a priori into
four groups (“warm”, “cool”, “cold”, and “oasis”) based on local elevation
and microclimatic differences that result in differing lengths of the
ice-free season, as well as about three decades of personal observations.
We characterized the species changes as a shift from Condition 1 (i.e. a
generally low diversity, predominantly epipelic and epilithic diatom
assemblage) to Condition 2 (i.e. a typically more diverse and ecologically
complex assemblage with an increasing proportion of epiphytic species).
This shift from Condition 1 to Condition 2 was a consistent pattern
recorded across the sites that experienced a change in ice cover with
warming. The “warm” sites are amongst the first to lose their ice covers
in summer and recorded the earliest and highest magnitude changes. The
“cool” sites also exhibited a shift from Condition 1 to Condition 2, but,
as predicted, the timing of the response lagged the “warm” sites.
Meanwhile some of the “cold” sites, which until recently still retained an
ice raft in summer, only exhibited this shift in the upper-most sediments.
The warmer “oasis” ponds likely supported aquatic vegetation throughout
their records. Consequently, the diatoms of the “oasis” sites were
characterized as high-diversity, Condition 2 assemblages throughout the
record. Our results support the hypothesis that the length of the ice-free
season is the principal driver of diatom assemblage responses to climate
in the High Arctic, largely driven by the establishment of new aquatic
habitats, resulting in increased diversity and the emergence of novel
growth forms and epiphytic species.