Permafrost regions are known to be susceptible to recent climate warming particularly with regard to positive feedback mechanisms (e.g. by the potential release of stored carbon) from permafrost. However, little is known about the potential of permafrost ice so called ground ice to store climate and environmental changes. Stable water isotope methods can under certain circumstances reveal climate information from permafrost ice and trace the changes through time. Stable water isotopes (δD, δ18O) are well established as mostly relative paleotemperature proxies for climate studies related to ice caps and glaciers in Greenland, Antarctica and other parts of the world. For permafrost research, the water isotopes have yet been underutilized.Ground ice is defined as all types of ice contained in frozen or freezing ground, including pore ice, segregated ice, as well as ice wedge ice. Ice wedges are most promising as paleoclimate archives. They are distinctive due to their vertically-oriented foliations and air bubbles. Ice wedges form as winter thermal contraction cracks are periodically filled by surface water (mainly from snow melt), which quickly (re)freezes at negative ground temperatures. The seasonality of thermal contraction cracking and of the infill of frost cracks are generally related to winter and spring, respectively. Ice wedges are, thus, assumed to be indicative of winter climate conditions. The processes involved are most likely free of any fractionation during freezing. Segregated ice forms by the process of ice segregation (motion of ground water in the sediment column towards a freezing front). Segregated ice is rather a mixture of winter and summer precipitation, which additionally has undergone fractionation during freezing. One must bear in mind that ground water in permafrost regions is mostly related to the active layer (a sub meter to meter thick layer, which melts in summer and freezes in winter). A third type of ground ice, so called pore ice also known as ice cement, is also intrasedimental ice occurring in the pores of soils, which was formed in situ (without water migration towards a freezing front). This type of ice is typical for relatively coarse-grained sediment. Here, also ground water is the main water source. All these different types of ground ice have a different genetic background, which can be traced by stable isotope methods. This includes the type of water involved (e.g. summer vs. winter precipitation, with relevant isotopic composition) as well as the amount of fractionation occurring during phase transitions in the water cycle. Under favorable conditions (such as minimal fractionation during freezing) the stable isotope composition of these different types of ground ice can be used as paleo archive: (1) for the differentiation of stratigraphical units i.e. Holocene ground ice being generally 3 to 7 heavier in δ18O than Pleistocene ground ice, (2) as centennial-scale climate archives for paleotemperature reconstruction as well as indication of (3) changing atmospheric moisture sources from climate-relevant d excess (d excess = δD-8*δ18O) records. In this paper, we tackle the potential of the different types of ground ice from Siberian and North American permafrost to trace past climate changes from relative isotope variations in intrasedimental ice to a detailed high-resolution winter climate record from Alaskan ice wedges for the Late Glacial-Holocene transition.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL7-From permafrost to deep sea in the Arctic