Description: This dataset contains hydrographical, biogeochemical and bioptical data from four field campaigns to the Mackenzie Delta region from spring to fall in 2019. Focus of the sampling was put on surface waters to compare with satellite imagery and capture the signal of the Mackenzie River water throughout the coastal waters of the Beaufort Sea. The water samples for the biogeochemical data were taken using pumps or niskin bottles. The repeated sampling focused on the two main outflow regions of the Mackenzie River: Shallow Bay and Mackenzie Bay in the west and Kugmallit Bay in the east as well as on the river channels across the delta. Most sampling locations were revisited four times. Sampling during different seasons was extremely challenging in this region due to uncertain ice cover and broken ice fields during and after ice break-up. Additionally, very shallow water (〈5 m) mandates the use of small draught boats, which was challenging under frequently harsh weather conditions. To tackle these challenges, various sampling platforms were used such as small boats, trucks, ski-doos and hovering helicopter. The campaigns were carried out under the umbrella of the EU Horizon 2020 project Nunataryuk.

Description: 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 River watershed of northwestern Canada, coupled with increases in river discharge and coastal erosion, triggers 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 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 breakup in summer, and 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, namely 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 and DOC), and colored 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, CDOM 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 (10.1594/PANGAEA.937587).