Organic matter incorporation into sea ice and potential matter release into the nearshore zone of the southern Beaufort Sea, Canada

Global warming, mainly caused by human influences, has become much more severe in recent decades. While the average temperature of the Earth has increased of about 0.8°C over the time period of the entire last century, the temperature has increased by 0.6°C over only the past 30 years (GISTEMP, 2016; Lenssen et al., 2019). The Arctic region has warmed more than twice as fast as the global average (Serreze et al., 2009; Screen and Simmonds, 2010). This accelerated heating has dramatic effects on a wide range of fields including the thawing and re-freezing processes of permafrost soils. Almost a quarter of the land area of the northern hemisphere is influenced by permafrost at around 23 million km2. When the permafrost thaws, the active layer deepens and the annual thawing phase of the permafrost soils becomes longer. A result of the thawing is the associated soil water mobility and an increased rate of erosion, causing more sediment and dissolved organic carbon (DOC) to be deposited in lakes, rivers, groundwater fluxes and coastal waters. In this work, sea ice cores and water from the water column below were sampled from the coastal area in the southern Canadian shelf of the Beaufort Sea, near Herschel Island - Qikiqtaruk, in order to investigate the possible incorporation of organic substances and the release from winter land-fast ice. The samples were collected from two intersecting transects, before the beginning of the melting season in spring 2019. Analyses of DOC, colored dissolved organic matter (CDOM), salinity, water isotope ratios as well as suspended particulate matter (SPM) were made, to gain information on how organic matter has been incorporated and released during the winter freeze up and through the season. The measured DOC-, CDOM- and SPM-concentrations are relatively low compared to sea ice concentrations measured in other studies. Isotopes and salinity measurements show decreasing freshwater and river influences at the south side of transect 1 through the winter, meaning that the freshwater source petered out through the course of winter and through that giving indication of the river as the organic matter source. Results also showed a significantly higher SPM concentrations at the near shore north side of transect 1 and the west near shore side of transect 2. The data obtained from this study show how sensitive the regions of the Arctic and their material and carbon fluxes react to rising temperatures and suggest that coastal erosion can occur already as early as part of the winter season.

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