Arctic Zooplankton Variability and Particle Fluxes Related to Atlantification in Kongsfjorden, Svalbard

The Arctic Ocean is warming faster than other areas as changes in oceanographic and climate regimes have a synergistic effect and become amplified, imposing characteristics of sub-arctic and temperate regions. The “Borealization” of the Arctic follows its Atlantification and is changing the species composition at different trophic levels. These aspects are analysed in this study in Kongsfjorden, Svalbard, where effects of climate change and Atlantification are known since 1990. Samples collected in 2021-2022 by an oceanographic mooring have been compared with data from the same sampling site in 2016-2017 to detect variations in the zooplankton community and in particle fluxes. Results show two environmental-climatic patterns: the Arctic regime in 2021-2022 and the Atlantic one in 2016-2017. The Arctic regime has both greater biodiversity, dominated by ctenophores, and inter-annual changes than the Atlantic one, defined by a low biodiversity and a dominance of copepods. Particle fluxes follow a similar seasonality in both years, but they are 2 orders of magnitude more intense in the Arctic regime than the Atlantic one. Inorganic particles derive from glacial and sea ice dynamics, increasing in summer due to Atlantic Waters (AW) inflow and air temperatures above the freezing point. The sampled organic matter has primarily a marine origin and is more degraded in the Atlantic regime than the Arctic one, probably due to AW pulses which led impoverished particles from sub-polar waters. Long-term effects of Atlantification may also change the seasonal oceanography of the fjord and reduce the sea ice coverage. These aspects are strongly correlated with both lateral and vertical passive fluxes, which may change significantly between the Arctic and Atlantic regimes.