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This dataset contains hydrochemistry and absorption measurements from surface water bodies (standing and flowing water) from Herschel Island, Yukon, Canada collected in 2016 and Cape Bounty Arctic Watershed Observatory, Nunavut, Canada collected in 2017.The detailed methods will be found in the accompanying manuscript. Supplement to: Coch, Caroline; Juhls, Bennet; Lamoureux, Scott F; Lafrenière, Melissa J; Fritz, Michael; Heim, Birgit; Lantuit, Hugues (2019): Comparisons of dissolved organic matter and its optical characteristics in small low and high Arctic catchments. Biogeosciences, Biogeosciences, 16(23), 4535-4553

Coastal ecosystems in the Arctic are affected by climate change. As summer rainfall frequency and intensity are projected to increase in the future, more organic matter, nutrients and sediment could be mobilized and transported into the coastal nearshore zones. However, knowledge of current processes and future changes is limited. We investigated streamflow dynamics and the impacts of summer rainfall on lateral fluxes in a small coastal catchment on Herschel Island in the western Canadian Arctic. For the summer monitoring periods of 2014-16, mean dissolved organic matter (DOM) flux over 17 days amounted to 82.7 ± 30.7 kg km**-2 and mean total dissolved solids flux to 5252 ± 1224 kg km-2. Flux of suspended sediment (SS) were 7245 kg km**-2 in 2015, and 369 kg km**-2 in 2016. We found that 2.0 % of SS was composed of particulate organic carbon. Data and hysteresis analysis suggests a limited supply of sediments; their interannual variability is most likely caused by short-lived localized disturbances. In contrast, our results imply that DOC is widely available throughout the catchment and exhibits positive linear relationship with runoff. We hypothesize that increased projected rainfall in the future will result in a similar increase of DOC fluxes. Supplement to: Coch, Caroline; Lamoureux, Scott F; Knoblauch, Christian; Eischeid, Isabell; Fritz, Michael; Obu, Jaroslav; Lantuit, Hugues (2018): Summer rainfall DOC, solute and sediment fluxes in a small Arctic coastal catchment on Herschel Island (Yukon Territory, Canada). Arctic Science Water samples were collected at the outflow of Ice Creek West on Herschel Island, Yukon Territory, Canada in the summers of 2014, 2015 and 2016 using an automatic water sampler (ISCO 3700).

As the Arctic coast erodes, it drains thermokarst lakes, transforming them into lagoons, and, eventually, integrates them into subsea permafrost. Lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions. In this research, borehole data, electrical resistivity surveying, and modeling of heat and salt diffusion were carried out at Polar Fox Lagoon on the Bykovsky Peninsula, Siberia. Polar Fox Lagoon is a seasonally isolated water body connected to Tiksi Bay through a channel, leading to hypersaline waters under the ice cover. The boreholes in the center of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik, a thin ice‐bearing permafrost layer, and unfrozen ground. The bathymetry showed that most of the lagoon had bedfast ice in spring. In bedfast ice areas, the electrical resistivity profiles suggested that an unfrozen saline layer was underlain by a thick layer of refrozen talik. The modeling showed that thermokarst lake taliks can refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0°C. This occurs, because the top‐down chemical degradation of newly formed ice‐bearing permafrost is slower than the refreezing of the talik. Hence, lagoons may precondition taliks with a layer of ice‐bearing permafrost before encroachment by the sea, and this frozen layer may act as a cap on gas migration out of the underlying talik. Supplement to: Angelopoulos, Michael; Overduin, Pier Paul; Westermann, Sebastian; Tronicke, Jens; Strauss, Jens; Schirrmeister, Lutz; Biskaborn, Boris K; Liebner, Susanne; Maksimov, Georgii M; Grigoriev, Mikhail N; Grosse, Guido (2020): Thermokarst Lake to Lagoon Transitions in Eastern Siberia: Do Submerged Taliks Refreeze? Journal of Geophysical Research-Earth Surface, 125(10)

The data set includes geochemical and hydrochemical information on individual permafrost and seawater samples from the Yukon Coast in the western Canadian Arctic used for an incubation experiment. The experiment mimicked erosion of permafrost coasts in the Arctic by mixing different kind of permafrost (i.e. organic-enriched and mineral) with ambient seawater at temperatures of 4 and 16°C during the course of 4 months (the approximate length of an Arctic open-water season). The data sets contain information on basic geochemical parameters measured before and after the experiment and on the production of greenhouse gases, which include carbon dioxide (CO2) and methane (CH4). The first data set contains the geochemical and hydrochemical data for permafrost and seawater as well as the total amount of CO2 and CH4 cumulated during the course of the experiment. The second data set contains information on the individual measurements of CO2 and CH4 (in ppm) with a gas chromatograph. The study aims at understanding the role of eroding permafrost coasts for the Arctic carbon cycle and budget. Supplement to: Tanski, George; Wagner, Dirk; Knoblauch, Christian; Fritz, Michael; Sachs, Torsten; Lantuit, Hugues (2019): Rapid CO2 Release From Eroding Permafrost in Seawater. Geophysical Research Letters

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.

River water is the main source of dissolved organic carbon (DOC) in the Arctic Ocean. DOC plays and important role in the Arctic carbon cycle and its export from land to sea is expected to increase with accelerated permafrost thaw with ongoing climate change. However, transport ways and transformation of DOC is mostly unknown. The absorption coefficient by colored dissolved organic matter (aCDOM) which can be used to estimate DOC concentration. In this study, we compiled DOC and aCDOM samples from 11 expeditions covering river, coastal and offshore waters.Water samples for DOC analysis were filtered through 0.7µm GF/F filter and acidified with 25 µL HCl suprapur (10 M) right after sampling. Samples were stored cool and dark for transport. DOC concentrations were measured using high temperature catalytic oxidation (TOC-VCPH, Shimadzu). Three measurements of each sample were averaged and after each 10 samples, a blank and a standard (Battle-02, Mauri-09 or Super-05 certified reference material from National Laboratory for Environmental Testing, Canada) were measured to sustain a quality control.Samples for aCDOM(λ) analysis were filtered through 0.22 µm Millipore GSWP filters (Gonçalves-Araujo et al., 2015, Lena 2016, Bykovksy 2017) or 0.7 µm Whatman GF/F (LD10, YS11, VB13, VB14, Lena 2014, Lena 2015) right after sampling. 100 ml filtrate was stored cool and dark in amber glass bottles until further analysis. aCDOM(λ) was measured with spectrophotometer (SPECORD 200, Analytik Jena) by measuring the absorbance (Aλ) in 1 nm intervals between 200 and 750 nm. The resulting absorbance measurements were then applied to a standard equation aCDOM (λ)=(2.303*A_λ)/L, where L is the path length (length of cuvette), to calculate the aCDOM(λ). Fresh Milli-Q water was used as reference. The cuvette length varied depending on the expected absorption in the sampled water (1 or 5 cm for river or coastal waters, 5 or 10 cm for offshore shelf waters). Resulting aCDOM spectra were corrected for baseline offsets by subtracting the absorption at 700 nm, assuming zero absorption at 700 nm. Supplement to: Juhls, Bennet; Overduin, Pier Paul; Hölemann, Jens A; Hieronymi, Martin; Matsuoka, Atsushi; Heim, Birgit; Fischer, Jürgen (2019): Dissolved organic matter at the fluvial–marine transition in the Laptev Sea using in situ data and ocean colour remote sensing. Biogeosciences, 16(13), 2693-2713

Detailed organic geochemical and carbon isotopic (d13C and D14C) analyses are performed on permafrost deposits affected by coastal erosion (Herschel Island, Canadian Beaufort Sea), and adjacent marine sediments (Herschel Basin) to understand the fate of organic carbon in Arctic nearshore environments. We use an end-member model based on the carbon isotopic composition of bulk organic matter to identify sources of organic carbon. Monte Carlo simulations are applied to quantify the contribution of coastal permafrost erosion to the sedimentary carbon budget. The models suggest that 36 % of all carbon released by local coastal permafrost erosion is efficiently trapped and sequestered in the nearshore zone. This highlights the importance of sedimentary traps in environments such as basins, lagoons, troughs and canyons for the carbon sequestration in previously poorly investigated, nearshore areas.

In July 2017, we collected apparent resistivity data (ohm-m) in a sub-aquatic permafrost environment on the southern coastline of the Bykovsky Peninsula in northeast Siberia. The project goal was to determine the depth to the top of frozen sediment for multiple submerged landscapes. The submerged landscapes included ice-rich Yedoma permafrost, permafrost that had undergone prior thermokarst (Alases), and a former lagoon (i.e. offshore at the lagoon's coastline positions in earlier years). The data was collected with an IRIS Syscal Pro Deep Marine resistivity system that was equipped with a GPS and an echo-sounder to record water depths. The geoelectric cable had an electrode separation of 10 m and the electrodes were arranged in a reciprocal Wenner Schlumberger array. The offset between the first electrode and the boat was approximately 10 m.