Mikhail Zakharov, 18 år, Sandnes
Skole: International School of Stavanger
Investigation of salinity impact on rate and amplitude of the seasonal water temperature changes in a fjord in Western Norway
This study is related to physics of fjords and lakes and touches upon physical processes of stratification and vertical mixing of water masses, which are studied more extensively in physical oceanography and limnology.
The study investigates how significant the impact of water salinity on rate and amplitude of the seasonal temperature changes in a fjord can be. Temperature data from a nearby freshwater lake is used as a benchmark.
It is assumed that the salinity gradient across the upper water layer in a fjord contributes to density stratification, which constrains vertical mixing of the surface waters and thereby accelerates and increases amplitude of the seasonal temperature changes.
Therefore, the research question is:
To what extent can salinity gradients affect the rate and amplitude of warming and cooling of the surface waters in a fjord as compared to a freshwater lake?
An experimental approach is taken. Seasonal temperature variations in a fjord and a lake are measured in the upper 30 m of water. In parallel, several salinity profiles are measured in a fjord in order to characterize the intensity of vertical mixing.
Analysis of the observed seasonal temperature trends shows that existence of the salinity gradients in a fjord is not the main factor which controls the intensity of vertical mixing. Hence, the rate and amplitude of warming and cooling of the surface waters do not strongly correlate with the salinity gradients.
The data suggests that substantially larger density gradients in a fjord are not able to stabilize the upper water column and restrict the intensity of vertical mixing.
Further analysis reveals that some other external forces bring additional energy and mix the upper water column in fjords, but not in lakes.
Since fjords are semi-open towards the sea, physical processes such as tides, estuarine circulation, aspiration and deep water renewal proved to be more influential in terms of vertical mixing and temperature control than the salinity gradients in fjords.
Heat flux from the sea and thermal energy storage in a fjord can also be seen on measured temperature profiles.