This study is part of ARCA (Arctic: present Climatic change and pAst extreme events) Project, an interdisciplinary project funded by the Italian Minister of Education and Research (MIUR), aiming to cross-different area and intervention to gain a wider overview on the climate change. The thesis concerns the analysis of a 6-year time series of particle fluxes in a small Arctic fjord of Svalbard (Kongsfjorden). Such information will be processed, and the data observed to date back to the sources. The nature of the particle supply allows us to understand the physical and biogeochemical dynamics of the inner fjord through which it will be possible to detect a potential correlation with the global change. To improve the knowledge about this extreme environment, a mooring array (Mooring Dirigibile Italia) and long-term sediment traps were installed in the inner bay, since 2010. A brief description of the study area and the framework of the thesis in terms of related research projects will be reported in Chapter 1, 2, 3. The methodologies for the preliminary treatment of the sediment trap samples and the processing of the dataset will be discussed in Chapter 4. Chapter 5 will summarize the thesis structure, and the results will be showed and discussed in Chapters 6 and 7 in the form of two main topics: the major source of particles and the mesozooplankton abundance, respectively. Finally, chapter 8 will report a final discussion highlighting the concluding remarks emerged by this research. Chapter 6. The Arctic Kongsfjorden, as many Svalbard’s fjords, experienced the climate warming with the ice-free and the retreat of glacier front. These phenomena lead to an increase in sediment supply. Continuous investigations for a long time series data collection are fundamental to understand the meteorological, biogeochemical and thermohaline dynamics inside the fjord. In 2010, the National Research Council, Institute of Marine Sciences (CNR – ISMAR) installed Mooring Dirigibile Italia in the inner fjord. An automatic sediment trap at the bottom depth was set for continuous investigations, together with current meters and thermometers at different depths. Our results suggest that, as the Arctic temperature rises in a warming scenario, the flux of glacier-derived material will increase accordingly. In particular, our time-series points towards the subglacial runoff driven by air temperature will be the dominant process affecting the glacier-fjord exchange of lithogenic material. Despite the light availability will likely increase due to the reduced sea-ice coverage, water column stratification modulated by the inflow of warm Atlantic waters will progressively increase and it will hamper the exchange of nutrients from the bottom waters. This, in turn, will severely reduce the biological production and in particular the primary productivity in the fjord. Concluding, this study highlighted the influence of the glaciers stress in Kongsfjorden. This forcing resulted to be more influent than other sources, such as the coastal debris runoff and the biological activity. As the melt-water supply in Kongsfjorden allows to an increase of settling particles, most of which lithogenic, it is predictable to expect an always greater input of them in the future, due to the global change. Chapter 7. The prerogative of our study is to have a continuous 6-year data set (2010 – 2016), showing the trend of zooplankton abundance and downward particles inside the fjord. The Mooring Dirigibile Italia have been deployed since September 2010 to May 2016 at 100m of water depth in the inner part of Kongsfjorden, Svalbard. Samples are collected from an automatic sediment trap set on it. The intact swimmers apparently enter actively in the sediment trap, so they cannot be considered in the passive flux. They are picked and identified at the order level to estimate their abundance over time. During May and June of each year, the maximum content of organic matter is recorded, symptom of a consistency with the solar activity. The δ13C variation indicated high contribution of marine organic matter in concomitance with the peaks of %OC. The Margalef index exhibited high values, sometimes reaching 1. This means that a discrete number of species per area occurs in Kongsfjorden, nevertheless it is an extreme environment. The trend in the abundance of the organisms is very heterogeneous over the time. The most abundant zooplankton group is Calanoida. At least five different groups occur in the samples, Calanus, Metridia, Aetideidae, Euchaetidae and Pseudocalanus, together with some unidentified specimen. The seasonal trend according to the annual Polar days and nights, show a high occurrence of Calanus sp., Appendicularians (Copelats) and Limacina Haelicina (Thecosomats) in the darkness periods. Rather, Amphipods, Euphausiids, Anellids and Chaetognaths abound during the light months. Even though the number of zooplankton in terms of flux should not be representative of the real abundance in the water column, our results provide useful information on seasonal and inter-annual variations of the epi-pelagic fauna composition in Kongsfjorden, Svalbard. The results revealed that solar irradiance, sea ice cover, turbidity and hydrodynamics, affect directly and indirectly on the marine biosphere, above all in a vulnerable region like the Arctic. The great amount of freshwater in summer makes the biological pump hard to work, with shifted time of phytoplankton bloom and cascading consequences on the primary consumers, and the subsequent trophic chain. Hence, the affecting stressors on the fitness of the individuals in Kongsfjorden are different. Concluding, the results show a changing in the magnitude of the species, due to the alteration of the ecological equilibrium of their niches. This is a good point since pelagic communities are mostly consumed by Arctic cod, tern and seal.
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|Titolo:||Temporal variability of particle fluxes in an Arctic fjord (Kongsfjorden, Svalbard): biogeochemical characterization of the trapped material|
|Appare nelle tipologie:||8.1 Tesi Dottorato|