Projectdetails

Annual growth of longlived (40-100+ yrs) evergreen polar shrubs can be used for high resolution climate reconstructions similar to tree-ring based climate reconstructions at lower latitudes. Transfer relationships between tundra plant growth characteristics and climate factors are obtained from experimental warming and correlative analyses in polar climate zones. Air temperature in the arctic tundra ecosystems is enhanced 1-1.5 oC with ITEX Open Top Chambers. The new climate multi-proxy consists of Annual Growth Increments (AGIs) and Winter Mark Distances (WMDs) and delta18O and delta2H values of annually grown plant segments. We study three evergreen polar shrubs: Cassiope tetragona and Empetrum nigrum in the Arctic and Empetrum rubrum in the (sub) antarctic, with a focus on Cassiope. By low polar temperatures and permafrost conditions stems of the evergreen shrubs studied are well preserved in soil cores for decades and ages (upto 600 yrs B.P C-14 dated). In our preparatory research temperature reconstructions based on Annual Growth Increments (AGIs) and Winter Mark Distances (WMDs) of the past decades and centuries have been obtained. The resolution of AGI and WMD of living (extant) Cassiope-based temperature reconstruction is 1 year, when WMDs from a soil core are used the resolution varies (5-15 years). Annual growth of Cassiope measured as WMDs of the past 20 years appeared to anticorrelate with the index of Summer Arctic Oscillation (AO). This is in accordance with phase shifts of the AO (and North Atlantic Oscillation NAO) during the last 30 years. A positive phase of AO is associated with increased summer (rain) precipitation and reduced winter precipitation with expected increased values of 18O and 2H in plant segments of polar shrubs as a result. Increased summer rain is associated with increased cloudiness, low summer temperatures and reduced plant growth. The opposite holds for the negative phase of AO: reduced summer (rain), a decrease of delta18O and delta2H values and increased annual growth (Fig. 3). Field and climate room experiments are planned to relate annual growth of polar shrubs to variation of temperature, precipitation or global solar (PAR) radiation. WMDs (and delta18O and delta2H values) can also be measured of Cassiope stems preserved in the arctic soil profile, enabling further temperature and AO variation reconstruction on a decadal and centennial scale. Our AGI and WMD based temperature reconstructions will be compared with temperature reconstructions based on oxygen isotopes from ice-cores drilled on Svalbard (0-600) and existing arctic climate data since ca 1910. Based on these comparisons of temperature reconstruction climate scenarios (IPCC 2001; ACIA 2004) may be evaluated.

Artikelen

• (2009). UV-B absorbing compounds in present-day and fossil pollen, spores, cuticles, seed and wood. Evaluation of a proxy for solar UV radiation Photochemical & Photobiological. pp. 1233-1243
• (2009). Annual growth of Cassiope tetragona as a proxy for Arctic climate: developing correlative and experimental transfer functions to reconstruct past summer temperature on a millennial time scale. Global Change Biol. pp. 1703-1715