Improved Characterization of the Tundra Ecosystem Preserved in the Camp Century Ice Core Subglacial Sediment, Northwestern Greenland

Climate warming is rapidly transforming Arctic ecosystems and may trigger climate feedbacks in the future; therefore, paleovegetation records from past warm periods are critical to understanding ecosystem sensitivity to warming. Due to present ice cover, little is known about past ice-free ecosystems from Greenland. Cosmogenic 26Al/10Be and luminescence burial dating reveals that the fossil-rich subglacial sediment from the Camp Century ice core preserves evidence of tundra ecosystems that emerged during at least two ice-free events in northwestern Greenland, one <1.0 ± 0.1 Ma and another earlier between <3.2 ± 0.4 Ma and >0.7 to 1.4 Ma. The subglacial sediment contains plant macrofossils, including multiple bryophyte species, woody twigs, and graminoids. Tomenthypnum nitens and Polytrichum juniperinum are most abundant and other bryophytes include Amblystegiaceae mosses. Herbaceous remains are likely from sedges, but poor preservation precluded further identification. These assemblages indicate the presence of moist shrub tundra and wetland depressions. Here, we focus on identifying the tree or shrub species that produced compressed woody twig material that is abundant in the subglacial sediment. Using a scanning electron microscope (SEM), we determined that the wood cellular structure from one twig is from a two-year-old cross section of willow (Salix spp), based on diffuse porosity, the presence of simple perforation plates, and uniseriate vascular ray parenchyma. The presence of simple perforation plates eliminated other diffuse porous woods such as birch (Betula) or alder (Alnus), which are characterized by scalariform perforation plates. We also picked plantmacrofossils for cellulose extraction and analyzed their oxygen isotope ratio (18Ocellulose). Cellulose was extracted from two samples: herbaceous and bryophytic macrofossils were grouped and wood was extracted separately. Cellulose samples were analyzed for 18Ocellulose as a proxy for paleotemperature and hydroclimate and compared to the sediment pore ice enriched 18O ratios (-23.0 to -21.5 ). Pairing other proxies with improved characterization of the tundra ecosystem preserved in Camp Century subglacial sediment will allow us to constrain paleoclimate conditions during past ice-free events in northwestern Greenland.