Exploring the use of diatoms as a new environmental proxy in Arctic coastal ice cores - A first case study using the RECAP ice core

We have recorded consistent (but low) numbers and a diverse range of diatom taxa (siliceous algae) over a 400-year period in the RECAP ice core, drilled from the Renland ice cap on the east coast of Greenland. This is an exciting initial step in attempting a diatom-based environmental reconstruction for an Arctic ice core for the first time, since Greenland’s inland ice cores (e.g. NGRIP, GRIP) do not appear to contain diatoms in enough numbers. Our novel study investigated the period 1528 - 1940 AD (encompassing the Little Ice Age (LIA)) and we developed a method for extracting diatom taxa from the ice-core meltwater samples for identification. This was done by microscopy using standard taxonomic techniques. In summary, the RECAP LIA assemblage comprises 93 species, 36 genera and 11 families where Thalassiosira/Coscinodiscus, Aulocoseira, Pinnularia, Nitzschia, Luticola, Diadesmis, Staurosira, Achnanthidium, Psammothidium spp are the dominant genera. In this interval we found that Renland received air blown diatoms from both planktonic/benthic freshwater (80%) and planktonic marine (20%) sources. The freshwater species included aerophilic species (from damp environments), key indicators of exposed, environments and found widely in the Arctic. We observe that both total diatom numbers and species composition changes rapidly over time (i.e. decadal timescales), similar to other ice-core proxies, and with higher total numbers/yr between about 1780 and 1850 AD. Further analysis is required to establish a link to specific environmental variables, which could include aridity, wind strength or sea ice cover. We hypothesise that similar lower altitude, coastal ice cores from Greenland and Canada could be useful diatom repositories in the Arctic region.