Seasonal salinity increases on the shelf shape annual to decadal freshening in a Northeast Greenland sill fjord
Ruiz-Castillo, E.; Winding, M.S.; Sejr, M.; Mortensen, J.; Boone, W.; Rysgaard, S. (2026). Seasonal salinity increases on the shelf shape annual to decadal freshening in a Northeast Greenland sill fjord. Est., Coast. and Shelf Sci. 341: 110166. https://dx.doi.org/10.1016/j.ecss.2026.110166
In: Estuarine, Coastal and Shelf Science. Academic Press: London; New York. ISSN 0272-7714; e-ISSN 1096-0015
Understanding the physical hydrographic variability in Arctic sill-fjords is essential for disentangling their biogeochemistry and ecosystem functioning. Fjords, influenced by seasonal local and shelf processes, cannot be understood without addressing shelf dynamics. Here, we combined moorings, CTD casts and, δ18O and δ2H data from 2015 to 2021 to resolve seasonality in the sill-fjord Young Sound (YS) and the adjacent Northeast Greenland Shelf (GS). Thereupon, we elucidated the impacts of seasonal processes on annual to decadal hydrography in YS. Results show seasonal variability in the intermediate layer where freshening occurred during ice-melt and ice-free periods. In the upper basin, freshening started in ice-free conditions and continued through the ice-covered periods. In the ice-covered periods, salinity increased in shelf waters. Large salinity increases drove inflows that inundated YS basin down to 150-200 m, halting freshening, and incrementing salinity at annual timescales. Less pronounced salinity increases on the GS and respective inflows could not overcome prior cumulative seasonal salinity decrease resulting in inter-annual freshening. Comparisons with historic data indicate seasonal salinity fluctuations in the intermediate layer remained constant in the period 2010 to 2021. Between 50 and 200 m, the freshening trend starting in 2005 halted after 2014 due to relatively large salinity increases on the GS up to the ice-covered period of 2019-2020. Below 200 m freshening continued. Findings indicate that the annual to decadal changes in YS depend on whether seasonal salinity increases on the GS during ice-covered periods offset fjord freshening during ice-melt and -free periods.
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