Spatial variations in geochemical characteristics of the modern Mackenzie Delta sedimentary system

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Vonk, Jorien E., Giosan, Liviu, Blusztajn, Jerzy, Montlucon, Daniel, Graf Pannatier, Elisabeth, McIntyre, Cameron, Wacker, Lukas, Macdonald, Robie W., Yunker, Mark B., Eglinton, Timothy I.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: /dk/atira/pure/sustainabledevelopmentgoals/life_below_water; name=SDG 14 - Life Below Water; Arctic; Arctic Ocean; Canada; Mackenzie Delta; Mackenzie River; Beaufort Sea; Mackenzie river; Mackenzie Shelf
• Online Access: https://research.vu.nl/en/publications/3b58ff4f-6ffa-46ea-90cc-4f1b1aff3bb1; https://doi.org/10.1016/j.gca.2015.08.005; https://hdl.handle.net/1871.1/3b58ff4f-6ffa-46ea-90cc-4f1b1aff3bb1; http://www.scopus.com/inward/record.url?scp=84939246304&partnerID=8YFLogxK; http://www.scopus.com/inward/citedby.url?scp=84939246304&partnerID=8YFLogxK

The Mackenzie River in Canada is by far the largest riverine source of sediment and organic carbon (OC) to the Arctic Ocean. Therefore the transport, degradation and burial of OC along the land-to-ocean continuum for this riverine system is important to study both regionally and as a dominant representative of Arctic rivers. Here, we apply sedimentological (grain size, mineral surface area), and organic and inorganic geochemical techniques (%OC, δ 13 C-OC and δ 14 C-OC, 143 Nd/ 144 Nd, δ 2 H and δ 18 O, major and trace elements) on particulate, bank, channel and lake surface sediments from the Mackenzie Delta, as well as on surface sediments from the Mackenzie shelf in the Beaufort Sea. Our data show a hydrodynamic sorting effect resulting in the accumulation of finer-grained sediments in lake and shelf deposits. A general decrease in organic carbon (OC) to mineral surface area ratios from river-to-sea furthermore suggests a loss of mineral-bound terrestrial OC during transport through the delta and deposition on the shelf. The net isotopic value of the terrestrial OC that is lost en route, derived from relationships between δ 13 C, OC and surface area, is -28.5‰ for δ 13 C and -417‰ for δ 14 C. We calculated that OC burial efficiencies are around 55%, which are higher (~20%) than other large river systems such as the Amazon. Old sedimentary OC ages, up to 12 14 C-ky, suggest the delivery of both a petrogenic OC source (with an estimated contribution of 19±9%) as well as a pre-aged terrestrial OC source. We calculated the 14 C-age of this pre-aged, biogenic, component to be about 6100yrs, or -501‰, which illustrates that terrestrial OC in the watershed can reside for millennia in soils before being released into the river. Surface sediments in lakes across the delta (n=20) showed large variability in %OC (0.92-5.7%) and δ 13 C (-30.7‰ to -23.5‰). High-closure lakes, flooding only at exceptionally high water levels, hold high sedimentary OC contents (>2.5%) and young biogenic OC with a terrestrial or an ...