Soil carbon accretion along an age chronosequence formed by the retreat of the Skaftafellsjökull glacier, SE-Iceland

Abstract

Climate warming has led to glacial retreat worldwide, where surfaces exposed to the atmosphere are subjected to weathering, vegetation colonization and new soil formation. On young soils developing along the recessional path left by the Skaftafellsjökull glacier, SE-Iceland, we investigated the accretion of soil organic carbon (SOC) and nitrogen (N), representing an age chronosequence of 120years. In total, 54 sampling sites were distributed along three moraines deposited in 1890, 1945, and 2003. For comparison, soil samples were collected from nearby birch woodlands (Betula pubescens Ehrh.), representing soils in a mature ecosystem likely to establish on the moraines in the future. Results show that the average SOC and N concentrations increase with time and at faster rates over the latter part of the chronosequence period investigated (1945–1890). After 120yrs, the soil contains 1.1kgCm−2 in the surface layer (0–10cm), which is still about one third of the 3.2kgCm−2 in soil under the birch woodlands. The N stock estimated at 0.06kgNm−2 after 120yrs is almost one fourth of that under the woodlands. The data suggest that landscape affects vegetation establishment and in turn, both landscape and vegetation affect soil development. Thus, concentrations of SOC, N and noncrystalline oxalate extractable Al and Fe are higher within depressions in the proglacial landscape. The comparison of SOC stock in the moraine soils with that under the birch forest shows that the young proglacial soils still have a large potential to accrete SOC within the developing pedosphere. With the observed accrual rate of 9.1gCm−2yr−1 in the top at 10cm, it may take the moraine soils an additional period of 220yrs to accrue SOC stocks comparable with those under the birch forest. Given the fact that all Icelandic glaciers are receding, assessing SOC accretion in new soil formation may be important to off-setting the greenhouse gas emissions.