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- Title
Atlantic Inflow to the North Sea Modulated by the Subpolar Gyre in a Historical Simulation With MPI‐ESM.
- Authors
Koul, V.; Schrum, C.; Düsterhus, A.; Baehr, J.
- 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. Plain Language Summary: Earlier investigations on the causes of variability in the North Sea water properties have mostly focused on the role of the atmosphere. This follows from the general idea that shallowness of the North Sea makes it more responsive to wind speed and direction than the deeper ocean. In the present contribution, we identify variability in North Sea water properties other than that induced by the atmosphere. For our analysis, we use a historical simulation with a global coupled model for two reasons: (a) In the model, the connections between North Atlantic and North Sea are represented, which would not be the case in a regional model, and (b) the model provides a long continuous time series of water properties, which is not available from spatially and temporally scarce observations. We find that the strength of subpolar gyre (SPG) has an impact on the salinity of the North Sea. When the SPG is weak (strong), water from the subtropical (subpolar) North Atlantic dominates the inflow into the North Sea and thus increasing (decreasing) the salinity. This modulation of inflow properties happens at decadal periods and beyond and is largely independent of the amount of Atlantic water entering the North Sea. Key Points: Low frequency open ocean impact on the North Sea is revealed in a global coupled modelThe properties of Atlantic inflow to the North Sea follow changes in subpolar gyre strength, while the total inflow is wind drivenThe subpolar gyre signal in the Faroe‐Shetland Channel and the North Sea is more pronounced in salinity than in temperature
- Subjects
NORTH Sea; MERIDIONAL overturning circulation; OCEAN circulation; WATER masses; SALINITY
- Publication
Journal of Geophysical Research. Oceans, 2019, Vol 124, Issue 3, p1807
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2018JC014738