Abstract
The restructuring of planktonic communities towards an increasing share of small individuals is not only expected, but also already observed consequence of warming in the rapidly changing Arctic. Here we demonstrate a simultaneous study on the nano-, micro- and mesoplankton (divided into small and large), and corresponding size fractions of particles along a hydrographical gradient in the Isfjorden – the largest Spitsbergen fjord system. The sampling was performed in 7 following summers (2013-2019) from the main basin under the influence of Atlantic Waters (ISA station), up to Billefjorden – the innermost part affected by meltwaters from Nordenskioldbreen (BAB station). Our objective was to elucidate the composition and spatial patterns in distribution of plankton and particles (P&P) under various hydrographical regimes. Combining two laser-based measurements (LOPC and LISST) with standard plankton analysis allowed us to conclude that vertical hydrographical stratification and eddy activity were forcing either layered or patchy distribution of P&P. The concentrations of P&P measured by LISST (nano- and micro-) were lower than the abundance of the corresponding size fractions of protists, but they did not differ significantly among the stations due to different origin of P&P. Nevertheless, the decreasing trend in the abundance of both investigated mesoplankton fractions could be observed between the ISA and BAB stations, whereas the opposite tendency was noted for P&P. Moreover, the abundance of mesoplankton was equal to the concentrations of the corresponding size fractions of P&P at the ISA station and much lower than the LOPC counts at the BAB station, which points towards notable amount of marine aggregates in the glacial bay. Even if some observations alluded to P&P susceptibility to the local processes, the inter-annual variability in P&P distribution surpassed the differences between the sampling stations. It suggests that both the large-scale processes (i.e. intensified inflow of Atlantic Waters) and natural seasonal changes associated with subtle differences in sampling timing had a stronger influence on investigated plankton than local factors. This pioneering study, which links traditional and advanced methods, clearly demonstrated that such approach is convenient for tracking small-scale spatial patterns and inter-annual variability of P&P in the Arctic pelagial.
Highlights
The most rapid and substantial climate-related changes in marine ecosystems are observed at high latitudes, in the Arctic
The hydrographical properties of Isfjorden vary from year to year, depending on the intensity of the advection of Atlantic Waters (AW) (Walczowski and Piechura, 2011) and the extent of the mixing (Svendsen et al, 2002) with Arctic Waters from the Sørkapp Current, local water and additional freshwater input originating from melting glaciers (Saloranta and Svendsen, 2001; Pavlov et al, 2013)
Out of the seven investigated summers, in 2013 the lowest seawater temperatures were noted at each station in the water layer below 40 m, while opposite temperature pattern was found in the warmest 2014
Summary
The most rapid and substantial climate-related changes in marine ecosystems are observed at high latitudes, in the Arctic. The reduction of sea ice cover, retreat of glaciers and an intensified freshwater discharge with suspended sediments are among the most pronounced consequences of climate fluctuations in this polar region They are expected to result in strengthening of Arctic stratification and weakening of the large-scale ocean circulation (Murray et al, 2012; Straneo and Heimbach, 2013). Biological components of the west Spitsbergen coastal waters might be extremely vulnerable and potentially sensitive indicators of the environmental changes They are still not fully explored and the knowledge gap is the most apparent for Isfjorden - the largest Svalbard fjord system
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