Seasonal to decadal temperature variations in the Faroe—Shetland inflow waters

A 53-year hindcast simulation with a regional version of the Nansen Center version of the Miami Isopycnic Coordinate Ocean Model (MICOM) was conducted to explore the nature of the observed seasonal to interannual variations in the temperature of the poleward flowing Atlantic Water (AW) crossing the Iceland-Scotland Ridge (ISR). The simulated long-term temperature variations closely resembled observations south of the ridge (Rockall Trough), north of the ridge (Svinoy section), and in the Faroe-Shetland Channel (FSC). The simulated temperature on the Faroe Shelf was also compared to daily temperature observations from Mykines, revealing realistic long-term temperature variations, seasonal variations, and a seasonal modulation. The simulated time series in the FSC indicates that the phase and amplitude of the annual temperature cycle of the AW have varied by almost 1 month and 0.15°C between the 1960s and 2001, illustrating the difficulty in unambiguously removing the seasonal cycle from sparsely sampled time series. We argue that the simulated time series can be used to complement the observed time series in periods with sparse sampling. Specifically, the observation-based cold anomaly in the late 1960s and the warming in the early 1980s should be treated with caution. Finally, the analysis indicates that it is not advisable to survey the hydrographic section less than four times a year if reliable decadal-scale temperature variations are of interest.