Lichenometric studies on moraines in the Polar Urals

Abstract

Lichenometry was used to study fluctuations of six glaciers in the Polar Urals over the last millennium (viz: IGAN, Obrucheva, Anuchina, Shumskogo, Avsiuka and Berga glaciers). In order to estimate the growth rate of Rhizocarpon subgenus Rhizocarpon lichens we used recently deglaciated surfaces as calibration sites. These sites, on glacier forelands, were dated using topographic maps, aerial photographs (from 1953, 1958, 1960, 1968, 1973, 1989), terrestrial photogrammetry, field photographs (from the 1960s to 2005), and satellite images (from 2000 and 2008). We also used pits and quarries abandoned between the 1940s–1980s and a road built in the early 1980s as calibration sites. Optimum diametral growth rates of Rhizocarpon subgenus Rhizocarpon are estimated by the new curve to be c. 0.25 mm/year for the last 100 years, assuming linear growth as deduced from the shape of other curves from northern Scandinavia. Due to the lack of old control points we used a reconstructed mass balance curve (from 1816 to 2008) to indirectly constrain the age of pre-twentieth-century moraines. The following moraine groups were identified near the modern fronts of glaciers: ablation moraines de-glaciated during the last 40 to 60 years; lateral moraines formed in the early twentieth century (largest lichen diameter (DLL) = 20 mm), ice-cored moraines, probably from the 1880s (DLL= 24–26 mm); moraines probably deposited in the middle of the nineteenth century and c. 200 years ago (DLL= 30–33 mm and 44–47 mm, respectively); as well as several more ancient moraines (DLL= 70 mm, 90 mm and 110–153 mm) deposited during glacier advances of almost identical extent. According to our tentative lichenometric-age estimates most moraines were formed during the last 450 years – consistent with upper tree-limit altitude variations previously identified for this region. Glacier fluctuations in the Polar Urals are in agreement with tree-ring based reconstructions of summer temperature spanning the last millennium, and are also in tune with glacier behaviour elsewhere in the Northern Hemisphere