Atlantic Inflow to the North Sea Modulated by the Subpolar Gyre in a Historical Simulation With MPI‐ESM

Abstract

While the influence of the subpolar gyre (SPG) on thermohaline variability in the eastern North Atlantic is well documented, the extent and timescale of the influence of the SPG on North Sea is not well understood. This is primarily because earlier investigations on the causes of variability in the North Sea water properties mostly focused on the role of atmosphere and deployed regional models. Here using a historical simulation with the Max Planck Institute Earth System Model (MPI‐ESM), we investigate circulation and water mass variability in key regions, namely, the Rockall Trough and the Faroe‐Scotland Channel, which link the North Atlantic to the North Sea. We find that salinity covaries with advective lags in these three regions and that the northern North Sea salinity follows the Rockall Trough with a lag of 1 year. We show that recurring and persistent excursions of salinity anomalies into the northern North Sea are related to the SPG strength and not to the local acceleration of the inflow. Furthermore, we illustrate that the SPG signal is more pronounced in salinity than in temperature and that this simulated SPG signal has a period of 30–40 years. Overall, our study suggests that, at low frequency, water mass variability originating in the North Atlantic dominates changes in the North Sea water properties over those due to local wind‐driven volume transport.

Distinct Mechanisms Underlying Interannual to Decadal Variability of Observed Salinity and Nutrient Concentration in the Northern North Sea

“…When the SPG circulation is strong, the SPG shifts eastward, and the subpolar water masses dominate this region. This results in anomalous freshening of the ENA (Hátún et al, 2005;Koul et al, 2019). When the SPG is weak, the SPF shifts westward, and this region is dominated by subtropical water masses which lead to an increase in salinity.…”

“…Unlike the mechanism driving the interannual to decadal variability of salinity in the northern North Sea induced by advected North Atlantic water masses (Koul et al, 2019;Núñez-Riboni & Akimova, 2017), the controlling factors of nutrient concentrations are much more entangled, and nutrient concentrations in the northern North Sea and in the adjacent North Atlantic exhibit strong lateral gradients ( Figure 2). Even though an earlier database (Radach & Pätsch, 1997) showed these gradients in northern winter concentrations, the southern North Sea dominated the discussion (Brockmann et al, 1988).…”

Skilful prediction of cod stocks in the North and Barents Sea a decade in advance

“…The hydrography of Norwegian-Barents Seas is related to the Atlantic inflow across the Greenland-Scotland Ridge 45 . When the SPG circulation is weak, the proportion of subtropical waters in the Atlantic inflow through the Faroe Shetland Channel increases 34,46 . The resulting increase in the temperature of ambient water masses pushes the ice edge northwards 47,48 , which leads to increased productivity through extended periods of increased primary production and also due to expansion of feeding grounds.…”

“…GCMs [30][31][32] , there might be a high potential in predicting fish stocks. This prospect emerges from the influence of Atlantic inflow on both hydrography 33,34 and marine ecosystem of the North Atlantic shelf-seas, such as the North and Barents Sea 14,15 .…”

“…Statistically, this linkage is supported by the high correlation between the surface temperature of the SPG and TSB of Northeast Arctic cod (r=0.78, p=0.0435) with the SPG-temperature leading TSB by 7-years (Supplementary Figure S1 and S2), and consistent with previous work 35 . Dynamically, this linkage points to the influence of SPG circulation on the properties of Atlantic water crossing the Greenland-Scotland ridge heading towards downstream shelf-seas 33,34,40 .…”