Sedimentary ancient DNA from Kronotsky Peninsula: how sea ice, salinity
and insolation dynamics have shaped diatom composition and richness over
the past 20,000 years
Abstract
We traced diatom composition and diversity through time using diatom
derived sedimentary ancient DNA (sedaDNA) from eastern
continental slope sediments off Kamchatka (North Pacific) by applying a
short, diatom-specific marker on 63 samples in a DNA metabarcoding
approach. The sequences were assigned to diatoms that are common in the
area and characteristic of cold water. SedaDNA allowed us to
observe shifts of potential lineages from species of the genus
Chaetoceros that can be related to different climatic phases,
suggesting that pre-adapted ecotypes might have played a role in the
long-term success of species in areas of changing environmental
conditions. These sedaDNA results complement our understanding of
the long-term history of diatom assemblages and their general
relationship to environmental conditions of the past. Sea-ice diatoms
(Pauliella taeniata (Grunow) Round & Basson, Attheya
septentrionalis (Østrup) R.M.Crawford and Nitzschia
frigida (Grunow)) detected during the late glacial and Younger
Dryas are in agreement with previous sea-ice reconstructions. A positive
correlation between pennate diatom richness and the sea-ice proxy
IP25 suggests that sea ice fosters pennate diatom
richness, whereas a negative correlation with June insolation and
temperature points to unfavorable conditions during the Holocene. A
sharp increase in proportions of freshwater diatoms at
~11.1 cal kyr BP implies the influence of terrestrial
runoff and coincides with the loss of 42% of diatom sequence variants.
We assume that reduced salinity at this time stabilized vertical
stratification which limited the replenishment of nutrients in the
euphotic zone.