Sedimentation in arctic proglacial lakes: Mittivakkat Glacier, south-east Greenland

Abstract

Abstract:Several sediment cores were collected from two proglacial lakes in the vicinity of Mittivakkat Glacier, southeast Greenland, in order to determine sedimentation rates, estimate sediment yields and identify the dominant sources of the lacustrine sediment. The presence of varves in the ice-dammed Icefall Lake enabled sedimentation rates to be estimated using a combination of X-ray photography and down-core variations in 137 Cs activity. Sedimentation rates for individual cores ranged between 0 . 52 and 1 . 06 g cm À2 year À1 , and the average sedimentation rate was estimated to be 0 . 79 g cm À2 year À1 . Despite considerable down-core variability in annual sedimentation rates, there is no signi®cant trend over the period 1970 to 1994. After correcting for autochthonous organic matter content and trap eciency, the mean ®ne-grained minerogenic sediment yield from the 3 . 8 km 2 basin contributing to the lake was estimated to be 327 t km À2 year À1 . Cores were also collected from the topset beds of two small deltas in Icefall Lake. The deposition of coarse-grained sediment on the delta surface was estimated to total in excess of 15 cm over the last c. 40 years. In the larger Lake Kuutuaq, which is located about 5 km from the glacier front and for which the glacier represents a smaller proportion of the contributing catchment, sedimentation rates determined for six cores collected from the centre of the lake, based on their 137 Cs depth pro®les, were estimated to range between 0 . 05 and 0 . 11 g cm À2 year À1 , and the average was 0 . 08 g cm À2 year À1 . The longer-term (c. 100±150 years) average sedimentation rate for one of the cores, estimated from its unsupported 210 Pb pro®le, was 0 . 10±0 . 13 g cm À2 year À1 , suggesting that sedimentation rates in this lake have been essentially constant over the last c. 100±150 years. The average ®ne-grained sediment yield from the 32 . 4 km 2 catchment contributing to the lake was estimated to be 13 t km À2 year À1 . The 137 Cs depth pro®les for cores collected from the topset beds of the delta of Lake Kuutuaq indicate that in excess of 27 cm of coarse-grained sediment had accumulated on the delta surface over the last approximately 40 years. Caesium-137 concentrations associated with the most recently deposited (uppermost) ®ne-grained sediment in both Icefall Lake and Lake Kuutuaq were similar to those measured in ®ne-grained sediment collected from steep slopes in the immediate proglacial zone, suggesting that this material, rather than contemporary glacial debris, is the most likely source of the sediment deposited in the lakes. This ®nding is con®rmed by the 137 Cs concentrations associated with suspended sediment collected from the Mittivakkat stream, which are very similar to those for proglacial material.

Fluctuations of sediment accumulation rates in front of an Arctic delta in Greenland

“…The coupling between the stratigraphy and the chronology based on two geo-chronological methods looked very promising (Figure 5). Similar good results between laminations and 210 Pb and 137 Cs derived age models for proglacial lacustrine sediment cores were observed in Icefall lake in the vicinity of the Mittivakkat Glacier (Hasholt et al, 2000). They interpreted the laminations as varves.…”

Extreme levels of fallout radionuclides and other contaminants in glacial sediment (cryoconite) and implications for downstream aquatic ecosystems

“…Despite several recent studies documenting elevated levels of FRNs in cryoconite in glaciers from Europe 5,9–17 , as far as we are aware no studies on elevated fallout contaminants in cryoconite have been conducted in North America. Furthermore, few studies have compared FRN concentrations in cryoconite to concentrations in fluvial sediments being actively transported in downstream proglacial rivers, to assess the broader environmental and ecological significance.…”

High‐resolution fjord sediment record of a receding glacier with growing intermediate proglacial lake (Steffen Fjord, Chilean Patagonia)

“…This would stand in contrast with the many studies that indicate that the formation of a proglacial lake generally results in a strong decrease in downstream sediment yield. For example, Hasholt et al (2000) estimated a trap efficiency of 90% for two lakes in south‐east Greenland, leading to considerably reduced sediment fluxes to the ocean. Geilhausen et al (2013) demonstrated that suspended sediment concentration decreased by up to 95% with the formation of a 0.2 km 2 proglacial lake in a 20 km 2 drainage area in Austria.…”