Dissolved organic carbon (DOC) in Arctic ground ice

M Fritz,H Lantuit,A Eulenburg,G Tanski,H Meyer,T Opel,U Herzschuh

doi:10.5194/tc-9-737-2015

Abstract

Abstract. Thermal permafrost degradation and coastal erosion in the Arctic remobilize substantial amounts of organic carbon (OC) and nutrients which have accumulated in late Pleistocene and Holocene unconsolidated deposits. Permafrost vulnerability to thaw subsidence, collapsing coastlines and irreversible landscape change are largely due to the presence of large amounts of massive ground ice such as ice wedges. However, ground ice has not, until now, been considered to be a source of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and other elements which are important for ecosystems and carbon cycling. Here we show, using biogeochemical data from a large number of different ice bodies throughout the Arctic, that ice wedges have the greatest potential for DOC storage, with a maximum of 28.6 mg L−1 (mean: 9.6 mg L−1). Variation in DOC concentration is positively correlated with and explained by the concentrations and relative amounts of typically terrestrial cations such as Mg2+ and K+. DOC sequestration into ground ice was more effective during the late Pleistocene than during the Holocene, which can be explained by rapid sediment and OC accumulation, the prevalence of more easily degradable vegetation and immediate incorporation into permafrost. We assume that pristine snowmelt is able to leach considerable amounts of well-preserved and highly bioavailable DOC as well as other elements from surface sediments, which are rapidly frozen and stored in ground ice, especially in ice wedges, even before further degradation. We found that ice wedges in the Yedoma region represent a significant DOC (45.2 Tg) and DIC (33.6 Tg) pool in permafrost areas and a freshwater reservoir of 4200 km2. This study underlines the need to discriminate between particulate OC and DOC to assess the availability and vulnerability of the permafrost carbon pool for ecosystems and climate feedback upon mobilization.

Highlights

Vast parts of the coastal lowlands of Siberia, Alaska and Canada consist of unconsolidated organic-rich, fine-grained deposits
The highest dissolved organic carbon (DOC) concentrations were found in ice wedges with a mean of 9.6 mg L−1 www.the-cryosphere.net/9/737/2015/
Together with average DOC concentrations of 11.1 mg L−1 this would lead to 5.3 g DOC m−3 for late Pleistocene ice wedges in the upper late Pleistocene permafrost column (Table 3) and a DOC pool of 43.0 Tg DOC based on 416 000 km2 of undisturbed Yedoma in Beringia and a mean thickness of 19.4 m (Strauss et al, 2013)

Summary

Introduction

Vast parts of the coastal lowlands of Siberia, Alaska and Canada consist of unconsolidated organic-rich, fine-grained deposits. These sediments, which occur as glacigenic and Yedoma-type sediments (including their degradation forms as thermokarst), are characterized by high ground-ice contents, both on a volumetric (vol %) and gravimetric (wt %) basis (Brown et al, 1997; Zhang et al, 1999; Grosse et al, 2013; Schirrmeister et al, 2013). Combining ice wedges and other ice types in Yedoma deposits gives a mean volumetric ground-ice content for those regions between 60 and 82 vol % (Zimov et al, 2006a, b; Schirrmeister et al, 2011b, c; Strauss et al, 2013).

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