Deglaciation and catchment ontogeny in coastal south‐west Greenland: implications for terrestrial and aquatic carbon cycling

Abstract

Here we present Holocene organic carbon, nitrogen, sulphur, carbon isotope ratio and macrofossil data from a small freshwater lake near Sisimiut in south-west Greenland. The lake was formed c. 11 cal ka BP following retreat of the ice sheet margin and is located above the marine limit in this area. The elemental and isotope data suggest a complex deglaciation history of interactions between the lake and its catchment, reflecting glacial retreat and postglacial hydrological flushing probably due to periodic melting of local remnant glacial ice and firn areas between 11 and 8.5 cal ka BP. After 8.5 cal ka BP, soil development and associated vegetation processes began to exert a greater control on terrestrial-aquatic carbon cycling. By 5.5 cal ka BP, in the early Neoglacial cooling, the sediment record indicates a change in catchment-lake interactions with consistent d 13 C while C/N exhibits greater variability. The period after 5.5 cal ka BP is also characterized by higher organic C accumulation in the lake. These changes (total organic carbon, C/N, d 13 C) are most likely the result of increasing contribution (and burial) of terrestrial organic matter as a result of enhanced soil instability, as indicated by an increase in Cenococcum remains, but also Sphagnum and Empetrum. The impact of glacial retreat and relatively subdued mid-to late Holocene climate variation at the coast is in marked contrast to the greater environmental variability seen in inland lakes closer to the present-day ice sheet margin.

Lake and catchment response to Holocene environmental change: spatial variability along a climate gradient in southwest Greenland

“…At AT1, C AR decreased substantially from * 5,700 cal year BP, possibly reflecting greater nutrient retention by the marginal soaks, which also reduced minerogenic sediment input. The timing of this change agrees with indications of catchment changes at a nearby lake (Sisi12), where the C/N ratio increased to [10, and there was greater abundance of Empetrum nigrum remains after 5,500 cal year BP (Leng et al 2012). More abundant Cenococcum sp.…”

“…The problem of climate inference is not helped by the number of single site studies that fail to consider regional variability and representativity. The problem is further exacerbated by the recognition that Neoglacial cooling, even in the absence of anthropogenic-driven land-cover change, causes substantial landscape degradation with increased erosional inputs and terrestrial carbon transfer from land to lakes (Andresen et al 2004;Leng et al 2012;McGowan et al 2008;Petterson et al 2010;Rubensdotter and Rosqvist 2003).…”

The Importance of Eolian Input on Lake-Sediment Geochemical Composition in the Dry Proglacial Landscape of Western Greenland

“…The most likely interpretation is that PC-3 represents the redox conditions in the bottom waters, where less oxygen in the bottom waters would favor the incorporation of S as sulfides in the sediment (Holmer and Storkholm, 2001;Leng et al, 2012). For P, the opposite behavior would be expected, with oxic conditions favoring incorporation of P bound to iron hydroxides and oxyhydroxides, and anoxic or hypoxic conditions resulting in dissolution of iron hydroxides and a release of P to the water column (Davison, 1993;Hupfer and Lewandowski, 2008).…”

Plant Water δD and δ18O of Tundra Species from West Greenland

“…1) spans ~30 km from Kangerlussuaq to the edge of the GrIS and mostly comprises low hills of exposed rock or glacial outwash and floodplain terraces (Storms et al, 2012). Deglaciation of the Søndre Strømfjord began around 10-11 kyr B.P., coupled with the advance of tundra vegetation (Anderson et al, 2008;Leng et al, 2012), and reached the Kangerlussaq area around 8 kyr B.P. (Bennike and Björck, 2002).…”