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Mackenzie Delta Lake sediments – Records of recent permafrost thaw?

Lay summary

Arctic rivers and especially their deltas are very dynamic environments that are vulnerable to the rapid changes the Northern regions are currently facing. The Mackenzie river in northwestern Canada is the largest source of suspended sediments and carbon to the Arctic Ocean. The abundant lakes within the Mackenzie delta are regularly flooded by the river, and lake sediments therefore record what is transported by the river and thereby provide information on processes and potential changes occurring within the river’s watershed. The Canadian Northwest Territories have witnessed unprecedented climate change over the last decade, with dramatic increases in temperature and precipitation leading to widespread thawing of previously frozen soils (permafrost). This begs the question as to whether fluxes and characteristics of materials exported from the Mackenzie river basin have changed in response to this changing climate. We propose to collect a suite of lake sediment cores from the Mackenzie delta in order to determine whether the materials discharged by the Mackenzie River and its tributaries have responded to recent climatic change, and in particular to seek evidence for mobilization of the vast stores of carbon held in permafrost within the watershed. The latter would represent an ominous sign of large-scale perturbations to the Arctic carbon cycle. To address these questions, we will apply a combination of geochemical and sedimentological techniques in order to constrain the flux, provenance, age and mobilization pathways of carbon and associated materials. Crucially, we plan to follow-up on recent field observations that hint at dramatic permafrost destabilization and release of aged carbon from tributaries of the Mackenzie. Provisional data provides only a “snapshot” from one point in time (spring season 2018), while lake sediment records provide continuous archives that will reveal whether this constitutes a “smoking gun” for a large-scale perturbation of the Arctic system.

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