At the northernmost point of Alaska, the Barrow area is one of the best-studied arctic regions, including permafrost research. However, stable isotope techniques have been used only sparsely, especially to characterise different types of ground ice. The application of hydrogen and oxygen isotopes for palaeoclimate studies in ice wedge ice is useful for reconstructing winter temperatures, whereas pollen reflect summer conditions. Ice wedges are principally formed by repeated frost cracking and percolation of meltwater of winter snow into frost cracks, forming ice veins, containing - under certain circumstances - the winter signal of the year of its formation.A small permafrost tunnel was excavated in the early 1960s by a CRREL team lead by one of the authors (Brown). The excavation into a massive complex of vertically foliated ice is at the 3- 6 m depth and is 9 m long. The tunnel was reopened in 2003 and sampled in 2004 by the Potsdam team for stable isotopes, sedimentological, palynological and microbiological analyses. Since in the 1960s neither AMS dating techniques nor stable isotope studies were readily available, the first step in our current investigations was to refine the age estimate of the site in order to improve our understanding of the genesis of the buried ice within the tunnel.Detailed results of geochronological, sedimentological and micropalaeontological studies reflect different stages of Late Pleistocene and Holocene palaeoenvironmental evolution. Isotope geochemistry indicates the intersection of two, isotopically different, ice wedges representing different phases of the regional climatic history, which extend to the Late Glacial Maximum. This is revealed by a new AMS date of 20,000 years at the lateral contact of the wedge and the surrounding sediments. A case study for the boundary top of ice wedge - sediment will demonstrate the importance of exchange processes, which may alter the original stable isotope signal.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL6-Earth climate variability since the Pliocene