Most of the warm water enters the Nordic Seas east and west of the Faroe Islands with the Shetland Current (SC) and the Faroe Current (FC). Both currents are monitored in the Svinøy section (SV).
The flow of warm water from the northern North Atlantic to the Nordic Seas is important for the regional climate. It contributes to the mild temperatures in our region and supplies nutrients to the marine ecosystem. By means of sea surface height observations it is possible to estimate a large part of the variability of the inflow, also back in time.
The bulk of the warm and saline Atlantic water enters the Nordic Seas in two branches, one over the Iceland-Faroe ridge (Faroe Current), and one between the Faroe and Shetland islands. It continues as the two-branched Norwegian Atlantic Current northward along the Norwegian coast where it is monitored in the Svinøy section.
Sea Surface Height
In a recent study presented in Journal of Geophyscial Research, Richter et al. showed that a large part of the changes in the warm water flow can be inferred from observations of sea surface height. The authors found that the sea surface height minimum in the Nordic Seas plays a crucial role in establishing the gradients that drive the inflow.
It is shown that the variability of the Faroe Current primarily responds to an oceanic regime dominated by steric height changes in the interior Nordic Seas. In contrast, variations in the Norwegian Atlantic Slope Current measured at the Svinøy section are largely driven by direct wind forcing that causes strong cross slope sea surface height gradients along the European shelf.
Back in time
The variability of the two sea surface height modes is captured by land-based tide gauges. Those can then be used to reconstruct inflow anomalies back in time. Respectively 22% (Faroe Current) and 38% (Svinøy Current) of volume transport variability can be explained using direct observations of sea surface height with tide gauges.
The results indicate that high inflow anomalies coincide with warm anomalies passing through the system and vice versa. Since volume transports toward the Nordic Seas are important with respect to the heat and freshwater budgets of the region, the reconstructed time series provide valuable insights into past climatic states of the region.
Observed volume transport anomalies (red) and anomalies inferred from sea level observations with tide gauges. Correlation coefficients between observed and reconstructed anomalies are given (values in parentheses refer to observation-independent reconstruction obtained from cross validation)
Reference
Richter, K., O. H. A. Segtnan, and T. Furevik (2012), Variability of the Atlantic inflow to the Nordic Seas and its causes inferred from observations of sea surface height, J. Geophys. Res., 117, C04004, doi:10.1029/2011JC007719.