Publications
Following ppubublication has been announced by our department Alkalinity. For further information please contact Dr Johannes Pätsch, author of the publication:
Pätsch, J., Gouretski, V., Hinrichs, I., & Koul, V. ( 2020): Distinct mechanisms underlying interannual to decadal variability of observed salinity and nutrient concentration in the northern North Sea. Journal of Geophysical Research: Oceans, 125, e2019JC015825, doi:10.1029/2019JC015825
Abstract:
The influence of large‐scale oceanic circulation on salinity in the northern North Sea has lead to the hypothesis that nutrient concentrations in this region are also driven by remote oceanic anomalies. Here, using a newly established biogeochemical data set of the North Sea, we show that interannual to decadal variability in winter nutrient concentrations exhibits distinct phase deviations from salinity. The variability in salinity is explained by zonal shifts in the position of the subpolar front (SPF) in the eastern North Atlantic and the associated advective delay. However, the high correlation and absence of advective delay between the position of the SPF and winter nutrient concentrations in the Shetland region (59–61°N, 1°W to 3°E) point to the role of atmospheric variability in driving concurrent changes in winter nutrient concentrations and the SPF position. Our analysis suggests that the prevailing wind direction and local distribution of winter nutrient concentrations together determine the interannual to decadal variability in winter nutrient concentrations in this region. In the analyzed observations, we find a strong spatial gradient in mean winter nutrient concentrations northwest of the Shetland region, which is absent in salinity. The horizontal shift of this spatial gradient, forced by changes in wind direction, has a larger influence on winter nutrient concentration in the Shetland region than the nutrient signal in oceanic anomalies originating from the eastern subpolar North Atlantic. Overall, we conclude that interannual to decadal variability in the observed nutrient concentrations is mainly driven by atmospheric variability here expressed as wind direction.
Plain Language Summary:
In many marine areas the winter concentration of nutrients determines the biological production of the following year. This is also true for the northern North Sea. Using a large data collection, we analyze salinity and nutrient concentrations there. We find salinity governed by the extension and retraction of a large gyre in the North Atlantic. We see consequences of the gyre dynamics 2 years later in salinity in the North Sea. Our idea was that nutrients behave similar with a time lag of 2 years. But we did not find this relation for nutrients. Instead, we find a surprising strong concurrent relation between nutrients in the North Sea and the North Atlantic gyre dynamics. As the oceanic signal cannot be transmitted without time lag, we investigate meteorological features, which work on both the eastern North Atlantic and the North Sea concurrently. We find wind direction induced by large meteorological pressure patterns, responsible for the variability of the gyre dynamics and local shifts of water masses with strong horizontal gradients in the northern North Sea. In summary, salinity variations in the northern North Sea are governed by large‐scale oceanic circulation, whereas winter nutrient variations are mainly driven by atmospheric variability.
