Plant colonization and response to late glacial abrupt climate change in south Greenland, viewed through leaf waxes and pollen

The late glacial to Holocene transition was a time of profound landscape change in the arctic punctuated by abrupt climate changes. In southern Greenland, land was exposed after local deglaciation and/or isostatic rebound during the Allerød interstadial. We present lipid biomarkers and pollen from 13.6 - 6 kcal years BP in rarely preserved postglacial lake sediments from lake N14 to document this transition. Lipid biomarkers include n-alkanes, acids, alcohols, HBIs, and cyclic isoprenoids and vary in absolute and relative abundance with time. While n-acids are the most abundant class, their chain length distributions are invariant through known climatic and vegetation changes, suggesting insensitivity to vegetation change in this system compared to dynamic n-alkane distributions. Late glacial lacustrine sediments contain abundant n-alkyl leaf waxes dominated by short chain (C21, 23) homologs and longer chain (presumably terrestrial plant-derived) waxes (C29, C31) at lower abundance. Pollen was sparce but reflects a pioneering assemblage dominated by Poaceae and Caryophyllaceae. From these we infer significant lacustrine primary production and local terrestrial vegetation during the Allerød. The Younger Dryas (YD) cold event, identified here previously in chironomid assemblages and reconstructed precipitation isotopes, is also clearly expressed in vegetation proxies. Lipid abundances drop and shift strongly towards short chain compounds, suggesting minimal terrestrial plant contributions. Pollen at this time was dominated by Poaceae with increases in cold-tolerant Dryas, Saxifragaceae, and Brassicaceae. Abrupt increases in lipid and pollen concentrations and diversity occurred at the start of the Holocene, followed by an enigmatic local cooling and decreased terrestrial productivity from 11.1 to 10.6 ka observed in chironomids, pollen, and lipid distributions. Subsequent establishment of modern-like Ericaceae and Betula shrub tundra beginning ~10.6 ka is recorded by increasing pollen abundance and diversity and increased relative and absolute abundance of long chain n-alkanes. Overall, n-alkanes and pollen record vegetation changes tightly coupled to late glacial and early Holocene climate as inferred from independent proxies.