Summer 2016 field season in the Blackstone Uplands

In July and August, Emma, Nathan, and Pascale visited the Blackstone Uplands, Yukon, to investigate field conditions at sites that showed signs of increased permafrost degradation between the 1950s and early 2000s. The data collected will be used for Emma’s honor thesis, as she will examine the distribution of thermokarst features in the Blackstone River valley and discuss terrain characteristics at the affected sites.

Photographs of thermokarst features in the Blackstone Uplands and some field work photos are found here, and more pictures of students hard at work in the field are found here. Nathan and Emma’s field work was made possible by funding from the Goodman School of Mines and the Northern Scientific Training Program. Thanks to the Na-Cho Nyak Dun and Tr’ondëk Hwëch’in First Nations for allowing us to conduct field work on their traditional territories.

Nathan and Emma 2016

Clockwise from top left corner: Degrading ice wedges and thermokarst tunnels; Expanding ponds; Active-layer detachment slides; Developping beaded streams. All photos taken in the Blackstone Uplands in 2016, by Pascale Roy-Leveillee.

 

Presentation on carbon input from lakeshore erosion at the 11th International Conference on Permafrost in Potsdam, Germany

Group photo for the 11th ICOP, in July 2016 (Credit: Alfred-Wegener-Institut/Jan Pauls)

Group photo for the 11th ICOP, in July 2016 (Credit: Alfred-Wegener-Institut/Jan Pauls)

 

 

The eleventh International Conference on Permafrost was held from June 20th to 24th in Potsdam, Germany. The conference was well attended with nearly 800 permafrost scientists and engineers, including many young permafrost researchers.

 

 

 

 

 

Eroding bank of a thermokarst lake in Old Crow Flats, Yk.

Eroding bank of a thermokarst lake in Old Crow Flats, Yk.

Pascale presented on the rates of organic carbon input in thermokarst lakes due to the erosion of shorelines in a tundra area of Old Crow Flats.This topic will be addressed in an up-coming paper co-authored with Elyn Humphreys, Zoe Braul, and Chris Burn. Preliminary results indicate that, in the area examined, approximately 0.22 teragrams of organic carbon fall in thermokarst lakes every year due to the erosion of the shorelines, including approximately 0.15 teragrams of organic carbon that was previously stored in permafrost.

New conceptual model for the genesis of drained thermokarst lake basin topography

 

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Examples of drained thermokarst lake basins with wet, depressed margins and drier ground near the basin centre (all pictures from Google earth): a) Fish Creek Area, Alaska; b) Tuktoyaktuk Peninsula, Northwest Territories; c) N Seward Peninsula, Alaska; d) Dewey Soper Bird Sanctuary, Baffin Island, Nunavut; e) Ayon Island, Chukotka, Siberia; f) Penzhina River area, Kamchatka Krai. Figure 2.6 from Roy-Leveillee, P. (2014) Permafrost and thermokarst lake dynamics in the Old Crow Flats, northern Yukon, Canada. Ph.D. Thesis, Carleton University: Ottawa, Canada.

A paper published by Roy-Leveillee and Burn (2016)  in Earth Surface Processes and Landforms  presents a new geomorphological model for the drained basin of thermokarst lakes in tundra areas.

Drained lake basins are widespread in Arctic lowlands affected by thermokarst and, in tundra areas, the topography of these basins typically constitutes a wet, depressed margin surrounding a slightly elevated, better drained centre. This low grade geomorphological feature is widespread in Arctic lowlands (see satellite images to the right), yet the genesis of this topography is poorly understood.

Based on conditions observed in Old Crow Flats, this new model suggests that patterns of sediment deposition along the lake bottom during lake expansion is what causes the raised centre and depressed margins revealed once permafrost is re-established in the drained basin floor (see diagram below).

This new model differs from that presented by Jorgenson and Shur based on observations of conditions in drained basins of the Alaska Coastal Plain. Their model relied on the poor frost-heave potential of gravelly sand which may accumulate near shore and the influence of shallow littoral terraces on permafrost configuration beneath lakes. This model raises the problem of equifinality, as similar topography develops in areas such as Old Crow Flats, where  lakes lack littoral shelves and develop in fine-grained glaciolacustrine silts (no sand or gravel).

This new conceptual model relies on a mechanism that is applicable in any location where lake shore bank erosion leads to the redistribution of sediment by wave action along the lake bottom. Differences in ground ice content may accentuate the elevation differences between basins and margins in some areas, as reported from the Beaufort Coastal Plain, but it did not in Old Crow Flats.

 

Ch6Fig15_model

Conceptual model of sedimentation patterns during thermokarst lake expansion (left) and resulting topography after lake drainage and permafrost aggradation (right). Sediment deposits that are in permafrost are marked with a light grey pattern. From Roy-Leveillee and Burn 2016, Fig 15.