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Qualitative and quantitative reconstruction of surface water characteristics and recent hydrographic changes in the Trondheimsfjord, central Norway

Authors

G. Milzer, J. Giraudeau, S. Schmidt, F. Eynaud, and J. Faust.

 

First Authors affiliation

EPOC


Journal

Climate of the Past

 10, 305-323, 2014

Special Issue


Abstract

In the present study we investigate 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 cysts is discussed in view of changes of the key surface water parameters sea-surface temperatures (SSTs) and sea-surface salinities (SSSs) monitored in the fjord, as well as river discharges. 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 hence 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 physico-chemical characteristics of the surface mixed layer. Still, discharges of major rivers were modulated, since 1985 by the implementation of hydropower plants which certainly influences the freshwater and nutrient supply into 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 SSTs and SSSs measured at 10 m water depth, as well as with mean annual PPs along the Norwegian coast and within Scandinavian fjords. The reconstructions are in general good agreement with the instrumental measurements and observations from other fjords. Major deviations can be addressed to peculiarities in the assemblages linked to the particular fjord setting and the related hydrological structure.


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