Can we predict fjord basin water renewals?
Authors/Creators
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1.
University of Bergen
Description
The water in the basin of sill fjords is renewed ocasionally. In some fjords, this renewal occurs irregularly while on others it has a more regular character. Independently of the renewal period, the renewal mechanism is thought to be common to all sill fjords: subsurface water outside of the fjord mouth lifted above the sill depth will trigger a renewal, provided that the lifted water mass is denser than the water in the basin. In Western Norway, the northerly, upwelling favourable winds that occur during Spring/Summer, provide a forcing for the uplifting of the isopycnals and bring dense, subsurface water to the upper water column, thereby creating the conditions for renewals to occur (Helle, 1980).
The renewal of sill fjord basins is an important aspect of the fjord ecological condition because it supplies oxygen rich water to the fjord basin, whose oxygen is consumed by the degradation of organic matter during the stagnant periods. Byfjorden (Figure 1) is the urban fjord in Bergen. It is heavily urbanized and has been consistenly showing lower oxygen levels in its basin (Figure 2), which has ecological implications (Johansen et al., 2018).
Byfjorden’s basin water is regularly renewed between the months of March and August, which makes it an attractive choice for the application of Deep Learning to predict basin water renewal in sill fjords. However, although Byfjorden’s observational period is long when compared to other fjords, there are significant gaps in the time series and the sampling frequency in most cases is suboptimal. In spite of these limitations, it is interesting to study the renewal process in the context of the atmospheric and hydrographic setting of the Norwegian coast.
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