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

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. 11calkaBP 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 post-glacial hydrological flushing probably due to periodic melting of local remnant glacial ice and firn areas between 11 and 8.5calkaBP. After 8.5calkaBP, soil development and associated vegetation processes began to exert a greater control on terrestrial-aquatic carbon cycling. By 5.5calkaBP, in the early Neoglacial cooling, the sediment record indicates a change in catchment-lake interactions with consistent δ ¹³C while C/N exhibits greater variability. The period after 5.5calkaBP is also characterized by higher organic C accumulation in the lake. These changes (total organic carbon, C/N, δ ¹³C) 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.