Abstract
Abstract. In the present study we investigated dinocyst assemblages in the Trondheimsfjord over the last 25 to 50 yr from three well-dated multi-cores (210Pb and 137Cs) retrieved along the fjord axis. The downcore distribution of the dinocysts is discussed in view of changes in key hydrographic parameters of the surface waters (sea-surface temperatures (SSTs), sea-surface salinities (SSSs), and river discharges) monitored in the fjord. We examine the impact of the North Atlantic Oscillation pattern and of waste water supply from the local industry and agriculture on the fjord ecological state and thus dinocyst species diversity. Our results show that dinocyst production and diversity in the fjord is not evidently affected by human-induced eutrophication. Instead the assemblages appear to be mainly controlled by the NAO-related changes in nutrient availability and the physico-chemical characteristics of the surface mixed layer. Still, discharges of major rivers have been modulated since 1985 by the implementation of hydropower plants, which certainly influences the amounts of nutrients supplied to the fjord. The impact, however, is variable according to the local geographical setting, and barely differentiated from natural changes in river run off. We ultimately test the use of the modern analogue technique (MAT) for the reconstruction of winter and summer SSTs and SSSs and annual primary productivity (PP) in this particular fjord setting. The reconstructed data are compared with time series of summer and winter SSTs and SSSs measured at 10 m water depth, as well as with mean annual PPs along the Norwegian coast and in Scandinavian fjords. The reconstructions are generally in good agreement with the instrumental measurements and observations from other fjords. Major deviations can be attributed to peculiarities in the assemblages linked to the particular fjord setting and the related hydrological structure.
Highlights
The climate of western Norway is closely coupled to the circulation of the topographically steered North Atlantic Current (NAC) and the Norwegian Coastal Current (NCC) flowing northward over the adjoining Norwegian shelf and continental margin (Loeng and Drinkwater, 2007)
According to the 210Pbxs-based dating, sediments at these depths correspond to an age of 1986 ± 1.7 yr and ca. 1963–1965 ± 3.4 yr, respectively, which is in good agreement with the known nuclear power plant accident in Chernobyl (1986) and the nuclear weapon test fallouts (Fig. 3)
Dinocyst assemblages from three sediment cores in the Trondheimsfjord show a high degree of coherency in terms of temporal succession
Summary
The climate of western Norway is closely coupled to the circulation of the topographically steered North Atlantic Current (NAC) and the Norwegian Coastal Current (NCC) flowing northward over the adjoining Norwegian shelf and continental margin (Loeng and Drinkwater, 2007). The lateral distribution and physico-chemical characteristics of the NCC, which is supplied by brackish water from the Baltic Sea, rivers and fjords along the Norwegian coast, are linked to the prevailing wind patterns in the North Atlantic realm (Sætre, 1999, 2007). The Trondheimsfjord in western central Norway adjoins the Norwegian Sea. The fjord hydrology is coupled to the NAC and NCC circulations, as well as to local riverine input from the hinterland (Sakshaug and Myklestad, 1973; Jacobson, 1983). The fjord sediments and incorporated fossil microorganisms provide highly resolved information on temporal changes in the fjord hydrology related to the proximal ocean current
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
