Arctic–Subarctic Ocean Fluxes: Defining the Role of the Northern Seas in Climate

Almost 100 years ago, Helland-Hansen and Nansen (1909) produced the first complete description of the pattern of oceanic exchanges that connect the North Atlantic with the Arctic Ocean through subarctic seas. At a stroke, they placed the science of the Nordic seas on an astonishingly modern footing; as Blindheim and Østerhus (2005) put it, ‘Their work described the sea in such detail and to such precision that investigations during succeeding years could add little to their findings’. Nonetheless, in the century that followed, oceanographers have gradually persisted in the two tasks that were largely inaccessible to the early pioneers – quantifying the exchanges of heat, salt and mass through subarctic seas and, piecing-together evidence for the longer-term (decade to century) variability of the system.

Evidence of variability was not long in coming. As hydrographic time series lengthened into the middle decades of the 20th century, they began to capture evidence of one of the largest and most widespread regime shifts that has ever affected our waters. For these were the decades of “the warming in the north”, when the salinity of North Atlantic Water passing through the Faroe–Shetland Channel reached a century-long high (Dooley et al. 1984), when salinities were so high off Cape Farewell that they were thrown out as erroneous (Harvey 1962), when a precipitous warming of more than 2 °C in the 5-year mean pervaded the West Greenland banks, and when the northward dislocations of biogeographical boundaries for a wide range of species from plankton to commercially important fish, terrestrial mammals and birds were at their most extreme in the 20th century (reviewed in Dickson 2002).