Glacial lake sediments: nice paleoenvironmental archives.

May 25, 2015 in @en , focus-en by fbouchard

Fig1-map

Figure 1: Location and context around kettle lake ‘BYL36’. The lake, containing sediments dated at 10.8 ka BP, is located just to the north-east (slightly upstream) of a terminal moraine dated at 9.8 ka BP (photos: V. Preskienis [upper] et GeoEye-1 [lower]).

The Holocene history of glacier valleys on Bylot Island, since the last glaciation, has been reconstructed by carefully studying the landscape features. For example, in the valley of glacier C-79 ( map, Figure 1 ), the maximum advance of the glacier was dated at 9860 ± 140 BP (before present), and it was suggested that the glacier front was in contact with shallow marine waters ( Allard, 1996 ). This interpretation is based on mollusc shells found in marine clay and dated using the radiocarbon ( 14 C) technique, which would give a ‘calibrated’ age of 11 440 ± 380 cal BP.

During the summer of 2014, Geocryolab members used a novel method of bathymetric mapping in order to characterize the morphology of a glacial lake located in the valley ( see other post about the sonar-GPS system ). It is a kettle lake, formed by the melting of ground ice buried in soil after glacier retreat, and located near the position of the glacier front mentioned above ( Fig1 ). A > 30-cm long sediment core ( Fig2 ) was collected from the deepest part of the lake (~ 12 m), and 14 C dating at the base of these lacustrine sediments gave an age of 10 825 ± 45 BP, or 12 730 ± 50 cal BP once calibrated. The exact nature of these sediments still has to be confirmed, but this shows the great potential of studying sedimentary archives contained in lakes. Which makes our friend ‘Zodiac Sherpa’ ( Fig3 ) very optimistic.

Fig2 Sediment core

Figure 2: Sediment core collected from the deepest part (~ 12 m) of kettle lake ‘BYL36’ (photo: F. Bouchard).

Fig3 Sediment Coring Sherpa

Figure 3 : Motivated young researcher who wisely checks, before jumping to the next coring site with a zodiac on his back, if he has all the equipment he needs. We can see the percussion corer just behind him (photo: V. Preskienis).

For further information:

Allard, M. (1996) : Geomorphological changes and permafrost dynamics: Key factors in changing arctic ecosystems. An example from Bylot Island, Nunavut, Canada. Geoscience Canada , 23, 205-212.

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Tags: Bylot , carbon , focus , kettle , lake

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