Hydrographic time series in the northeast North Atlantic and Nordic Seas show that the freshening trend of the 1960s–1990s has completely reversed in the upper ocean. Since the 1990s temperature and salinity have rapidly increased in the Atlantic Inflow from the eastern subpolar gyre to the Fram Strait. In 2003–2006 salinity values reached the previous maximum last observed around 1960, and temperature values exceeded records. The mean properties of the Atlantic Inflow decrease northwards, but variations seen in the eastern subpolar gyre at 57°N persist with the same amplitude and pattern along the pathways to Fram Strait. Time series correlations and extreme events suggest a time lag of 3–4 years over that distance. This estimate allows predictions to be made; the temperature of Atlantic water in the Fram Strait may start to decline in 2007 or 2008, salinity a year later, but both will remain high at least until 2010.

Ocean climate impacts on survivorship and growth of Atlantic salmon are complex, but still poorly understood. Stock abundances have declined over the past three decades and 1992-2006 has seen widespread sea surface temperature (SST) warming of the NE Atlantic, including the foraging areas exploited by salmon of southern European origin. Salmon cease feeding on return migration, and here we express the final growth condition of year-classes of one-sea winter adults at, or just before, freshwater re-entry as the predicted weight at standard length. Two independent 14-year time series for a single river stock and for mixed, multiple stocks revealed almost identical temporal patterns in growth condition variation, and an overall trend decrease of 11-14% over the past decade. Growth condition has fallen as SST anomaly has risen, and for each yearclass the midwinter (January) SST anomalies they experienced at sea correlated negatively with their final condition on migratory return during the subsequent summer months. Stored lipids are crucial for survival and for the prespawning provisioning of eggs in freshwater, and we show that under-weight individuals have disproportionately low reserves. The poorest condition fish ($ 30% under-weight) returned with lipid stores reduced by $ 80%. This study concurs with previous analyses of other North Atlantic top consumers (e.g. somatic condition of tuna, reproductive failure of seabirds) showing evidence of major, recent climate-driven changes in the eastern North Atlantic pelagic ecosystem, and the likely importance of bottom-up control processes. Because salmon abundances presently remain at historical lows, fecundity of recent year-classes will have been increasingly compromised. Measures of year-class growth condition should therefore be incorporated in the analysis and setting of numerical spawning escapements for threatened stocks, and conservation limits should be revised upwards conservatively during periods of excessive ocean climate warming.

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[1] A large part of the surface inflow to the Nordic Seas coalesces into a narrow slope current in the Färoe-Shetland Channel, and flows along the Shetland shelf edge with mean speeds of order 0.4 m/s. Observations reveal that the flow is unstable and forms large mesoscale meanders with current speeds of up to 0.9 m/s in a front between two water masses that lies along the channel. The meanders tend to form at two specific locations. Long-term analyses of drifter and altimeter archive data show hot spots in eddy kinetic energy that are greater than 300 cm 2 /s, and in surface elevation variance that are nearly 40 cm 2 . A baroclinic instability analysis suggests that the growth time of the meanders should be a few days, with a separation distance of order 65 km, and that their group velocity could be very close to zero depending on the strength of the southward outflow below 500 m. Thus, unlike their counterparts in the Norwegian Coastal Current, for example, the instabilities do not propagate. Decay of the anticyclonic meanders probably leads to the formation of cyclonic eddies that mix North Atlantic Water and Modified North Atlantic Water (MNAW) and create the more homogeneous forms of Atlantic water that are observed as the water moves northward through the channel and into the Norwegian Sea. Mesoscale driven entrainment may help to draw MNAW into the Färoe-Shetland Channel from around Färoe.

Climate variability in the Norwegian Sea was investigated in terms of ocean heat and fresh water contents of Atlantic water above a reference surface, using hydrographic data during spring 1951-2010. The main processes acting on this variability were examined and then quantified. The area-averaged water mass cooled and freshened, but a deepening of the reference surface resulted in a positive trend in the heat content of 0.3 W m À2 . Air-sea heat fluxes explained about half of the interannual variability in heat content. The effect of the advection of Atlantic and Arctic waters on the variability varied with time, apparently due to large-scale changes in the ocean circulation. The data are consistent with the explanation that changing wind patterns caused buffering and then release of Arctic water in the Iceland Sea during the late 1960s to early 1970s, and this caused large hydrographic changes in the Norwegian Sea.