Nunataryuk field campaigns: Understanding the origin and fate of terrestrial organic matter in the coastal waters of the Mackenzie Delta region

Abstract

Abstract. Climate warming and related drivers of soil thermal change in the Arctic are expected to modify the distribution and dynamics of carbon contained in perennially frozen grounds. Thawing of permafrost in the Mackenzie Delta region of northwestern Canada, coupled with increases in river discharge and coastal erosion, trigger the release of terrestrial organic matter (OMt) from the largest Arctic drainage basin in North America into the Arctic Ocean. While this process is ongoing, well-established, and its rate is accelerating, the fate of the newly-mobilized organic matter, as it transits from the watershed through the delta and into the marine system, remains poorly understood. In the framework of the European Horizon 2020 Nunataryuk programme, and as part of the Work Package 4 (WP4) Coastal Waters theme, four field expeditions were conducted in the Mackenzie Delta region and southern Beaufort Sea from April to September 2019. The temporal sampling design allowed the survey of ambient conditions in the coastal waters under full ice cover prior to the spring freshet, during ice break-up in summer, as well as anterior to the freeze-up period in fall. To capture the fluvial-marine transition zone, and with distinct challenges related to shallow waters and changing seasonal and meteorological conditions, the field sampling was conducted in close partnership with members of the communities of Aklavik, Inuvik and Tuktoyaktuk, using several platforms: helicopters, snowmobiles and small boats. Water column profiles of physical and optical variables were measured in situ, while surface water, groundwater and sediment samples were collected and preserved for the determination of the composition and sources of OMt, including particulate and dissolved organic carbon (POC, DOC), and chromophoric dissolved organic matter (CDOM), as well as a suite of physical, chemical and biological variables. Here we present an overview of the standardized datasets, including hydrographic profiles, remote sensing reflectance, temperature and salinity, particle absorption, nutrients, dissolved organic carbon, particulate organic carbon, particulate organic nitrogen, colored dissolved organic matter absorption, fluorescent dissolved organic matter intensity, suspended particulate matter, total particulate carbon, total particulate nitrogen, stable water isotopes, radon in water, bacterial abundance, and a string of phytoplankton pigments including total chlorophyll. Datasets and related metadata can be found in Juhls et al. 2021. https://doi.pangaea.de/10.1594/PANGAEA.937587.

Seasonal dynamics of dissolved organic matter in the Mackenzie Delta, Canadian Arctic waters: Implications for ocean colour remote sensing

“…For a detailed overview of the complete dataset resulting from the four campaigns we refer to Lizotte et al (2022).…”

Biogeochemical River Runoff Drives Intense Coastal Arctic Ocean CO2 Outgassing

“…This warming has dramatically altered Arctic watersheds and rivers, which play an important role in shaping the physical and biogeochemical setting of the coastal AO. Along with a 0.22% yr −1 intensification of river discharge since 1984 (Feng et al, 2021), accelerated permafrost thaw (Chadburn et al, 2017;Langer et al, 2022;McGuire et al, 2016;Slater & Lawrence, 2013) (a) changes the quantity and the quality (i.e., sources, compositions, and bioavailability) of tDOC exported to the AO (Mann et al, 2022;Matsuoka et al, 2022) and (b) increases connectivity between watersheds and marine ecosystems. Recent work shows that permafrost-driven carbon in the Mackenzie River mouth was observed even in early spring/summer, typically when only modern (i.e., young) organic matter has been observed (Schwab et al, 2020), highlighting the ongoing, rapid Arctic warming.…”