Morphology and properties of recent gelisols and palaeosols

Sebastian Zubrzycki, Anastasia Germogenova and Eva-Maria Pfeiffer Introduction

Permafrost-affected soils (Gelisols or Cryosols), which cover nearly one fourth of the terrestrial surfaces in the northern hemisphere play a major role in the global carbon cycle. About 14 % of the global organic carbon is stored in per-mafrost soils and sediments. Spatial distribution and genesis of soil types in the southern Lena Delta provide a basis for evaluation of the impact of environ-mental and climate change on permafrost landscapes. Based on an existing soil map of Island Samoylov of the year 2005 additional soils studies have been carried out during the expedition Lena 2007.

Investigation area

The investigation sites are located on Island Samoylov and Island Kurungnakh.

The islands are situated at one of the main Lena River channels, the Olenyok-skaya Channel in the southern part of Lena Delta. The Lena Delta is at the north coast of Siberia, where the Lena cuts through the Verkhoyansk Mountains Ridge and discharges into the Laptev Sea, which is part of the Arctic Ocean.

The Island Samoylov can be divided into two major geomorphological units.

There is a relative young floodplain in the western part that is annually flooded in spring and a higher-elevated river terrace of Late Holocene age, the ‘first’

terrace in the eastern part. The first terrace is flooded only during extreme high water events (Kutzbach, 2006).

The Island Kurungnakh belongs to the third river terrace complex of the Lena Delta. The third terrace is the oldest in the delta. It was formed in Middle and Late Pleistocene (Kuzmina et al., 2003; Wagner et al., 2003). This terrace forms autonomous islands along the Olenyokskaya and Bykovskaya Channels. The Island Kurungnakh is located at the southeastern end of Olenyokskaya Channel (Schwamborn et al., 2002).

The climate in the Lena Delta is true-arctic, continental and characterized by low temperatures and low precipitation. The mean annual air temperature, measured by the meteorological station in Tiksi located about 110 km to the south-east directly at the coast of the Laptev Sea, was -13.6°C (7.5°F) during the 30-year period 1961…1990; the mean annual precipitation in the same pe-riod was 319 mm. The average temperatures of the warmest month August and the coldest month January were 7.1°C (44.8°F) and -32.4°C (-26.3°F), respec-tively (Roshydromet, 2007), demonstrating the extreme climatic contrasts be-tween the polar day and polar night for continental Polar Regions.

Objectives

The goal of this study is to compare recent cryosols with palaeosols of deeper sediment layers of the Islands Samoylov and Kurungnakh.

Morphological and analytical data are taken into account to understand the properties and genesis of the buried soils of the ice rich permafrost sediments and recent soils in the southern Lena Delta.

A special consideration is put on different pedogenic formed iron-oxides. Re-search of different iron-oxides helps to estimate the conditions during which ac-tive pedogenesis took place. Palaeosols are often characterized by their iron-oxides fractions and data facilitates an estimate of the relative age of a given soil-sequence.

Material and Methods

The main soil unit of the first terrace above the floodplains of Island Samoylov is covered mainly by the soil-plant-complex Glacic Aquiturbels/ Typic Historthels.

The Typic Historthels are Gelisols that have in 30 % or more of the pedon more than 40 %, by volume, organic materials from the surface to a depth of 50 cm (Soil Survey Staff, 2006). They are situated in the depressed centers of low-centred ice-wedge polygons characterized by a water level directly at the soil surface and predominant anaerobic accumulation of organic matter. The Glacic Aquiturbels are situated at the elevated borders of the polygons and are charac-terized by a distinctly deeper water level, lower accumulation of organic matter, and pronounced cryoturbation properties. So Glacic Aquiturbels are Gelisols that have one or more horizons showing cryoturbation in the form of irregular, broken, or distorted horizon boundaries, involutions, the accumulation of or-ganic matter on top of the permafrost, ice or sand wedges, and oriented rock fragments. They have within 50 cm of the mineral soil surface, redox depletions with chroma of 2 or less and also aquic conditions during normal years and a glacic layer with its upper boundary within 100 cm of the mineral soil surface (Soil Survey Staff, 2006).

Close to the erosion cliffs various dryer and sandy soil complexes such as Psammorthels and Psammoturbels are typical. That means soils that have less than 35 %, by volume, rock fragments and a texture of loamy fine sand or coarser in all layers within the particle-size control section (Soil Survey Staff, 2006). Thermal erosion leads in that erosion cliff area to formation of high-centred polygons which are often covered by aeolian sands.

On Kurungnakh similar Glacic Aquiturbels and Aquic Histurbels as on Samoylov are typical. These recent soils are compared with paleosoils such as Histels of different decomposition, iron-rich Aquorthels and Aquiturbels of exposures on both islands. For investigations of soils two exposures of 7.10 and 5.40 m thick-ness were selected on Island Samoylov (Figure 3.4-1) and as well as two on Kurungnakh.

Figure 3.4-1: Exposure on Island Samoylov.

On Kurungnakh it was possible to collect samples of different age of genesis;

from 2.500 to 40.000 years BP; of exposures of 12 and 30 m thickness. Sam-ples of recent soils have been taken from the active layer as well as of palaeo-sols from above mentioned exposures. Additional, on Island Samoylov two soil-cross-sections of a high-centered and a low-centered polygon were investigated and compared with the recent soils of Island Kurungnakh.

Samples were collected from single layers of individual exposures. First pe-dological descriptions of Munsel-Color, hydromorphic features, bulk density, organic substance, roots, CaCO3 and fresh weight were done in field.

The oxalate-extractable iron (Feo) will be determined by the method of Schwertmann (1964) at room temperature, darkness with acid ammonium ox-alate at pH 3.25. The dithionite-extractable iron (Fed) will be determined by the DCB method of Mehra & Jackson (1960) with dithionite-citrate buffered by bi-carbonate at pH 7.3. Iron in all extracts will be determined by ICP-Emissions-Spectrometer. To make an estimate of the relative age of a soil-horizon using analysis of different forms of Fe, the following fractions will be used: Feo as “ac-tive” Fe-oxides, probably ferrihydrit, Fed minus Feo as Fe in less “active” well crystallised form, probably goethite and the ratio Feo/Fed as a degree of activity and pedogenesis.

3.5 Long-term studies on methane fluxes from permafrost