Abstract
Global warming is causing rapid changes to the cryosphere. Predicting
the future trajectory of the cryosphere requires quantitative
reconstruction of its past variations. A recently identified
sea-ice-associated haptophyte, known as Group 2i Isochrysidales, has
given rise to a new quantitative sea-ice proxy with its characteristic
alkenone distributions. However, apart from the occurrence of Group 2i
Isochrysidales in regions with sea ice, and the empirical relationship
between C37:4 alkenone abundance and sea-ice
concentration, little is known about the ecology of these haptophyte
species. Here, we systematically mapped the spatial and temporal
occurrence of known Group 2i Isochrysidales based on environmental DNA
and alkenones in both marine and lacustrine environments. Our results
indicate Group 2i is widely distributed in icy marine and lacustrine
environments in both Northern and Southern Hemisphere, but absent in
ice-free environments. Temporally, Group 2i is part of the sea-ice algae
bloom during the cold seasons, in contrast to other Isochrysidales that
bloom in open waters during warm seasons. Our results indicate that ice
is a prerequisite for the occurrence of the psychrophilic Group 2i
haptophytes in marine and lacustrine ecosystems and further affirms its
value for past ice reconstructions.