Reversal of the 1960s to 1990s freshening trend in the northeast North Atlantic and Nordic Seas

Abstract

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.

Simulated Response of the Arctic Freshwater Budget to Extreme NAO Wind Forcing

“…We also find that the increased export of 1300 km 3 yr 21 of freshwater to the North Atlantic in our NAO1 integration is approximately two-thirds of the rate of increased export found for the 5-yr GSA event beginning in the late 1960s, examined by Dickson et al (1988). Recent observations from Holliday et al (2008) indicate that the freshening trend of the North Atlantic has reversed since the mid1990s. This reversal comes at a time when the NAO became more neutral, suggesting that the reestablishment of the Beaufort gyre caused less freshwater to leak into the North Atlantic, compared to that in previous decades.…”

Near-Surface Transport Pathways in the North Atlantic Ocean: Looking for Throughput from the Subtropical to the Subpolar Gyre

“…Their analysis indicated an increase in the intergyre connectivity after 2001, from which they inferred a change in surface currents that opened new pathways from the western subtropical gyre to the subpolar latitudes. Although this conclusion is plausible and supported by observational evidence of an abrupt increase in salinities since 2002 in the Faroe2Shetland Channel and in the Rockall Trough (Holliday et al 2008), the increased number of crossings into subpolar latitudes since 2001 could also be explained by differences in drifter launch locations before and after 2001. We will elaborate on this point in the next section after presenting our analysis.…”

Intense warming and salinification of intermediate waters of southern origin in the eastern subpolar North Atlantic in the 1990s to mid‐2000s

“…Thus, the IW salinity changes at 60°N are (qualitatively) close to the upper-ocean salinity changes in the FaroeShetland Channel ($61°N), where salinity began to increase in 1996, reached a peak in 2004 (i.e., $1 year earlier than IW S) and showed a decrease in -2006[Holliday et al, 2008. Negative correlation between the SF longitude at 60°N and rmNAO (À0.77) during the considered decade corresponds to the close negative correlation (À0.81) between the SF longitude (at 55°N) and NAO on a decadal time scale [see Lozier and Stewart, 2008].…”