Sea surface temperature

To the Editor — e global ocean has absorbed 93% of the extra heat trapped by the Earth since 19701 and the rate of change in ocean heat content is a good estimate of the radiation imbalance at the top of the atmosphere2. Previously we reported3 a robust warming rate over the Earth’s area of 0.5–0.7 W m–2 during 2006–2014 using the global ocean data from the Argo array and three contrasting mapping methods: an optimal interpolation (OI), reduced space optimal interpolation (RSOI) and robust parametric t (RPF). We have extended these analyses over the additional 23 months of data from Argo to probe ocean heat content evolution through to November 2015.

The oceans have shown a recent rapid and accelerating rise in temperature with, given the close link between temperature and marine organisms, pronounced effects on ecosystems. Here we describe for the first time a globally synchronous pattern of pulsed short period (~1 year long) emanations of warm sea surface temperature anomalies from tropical seas towards the poles on the shelf/slope with an intensification of the warming after the 1976/1977, 1986/1987 and 1997/1998 El Niños. On the eastern margins of continents the anomalies propagate towards the poles in part by largely baroclinic boundary currents, reinforced by regional atmospheric warming. The processes contributing to the less continuous warm anomalies on western margins are linked to the transfer of warmth from adjacent western boundary currents. These climate induced events show a close parallelism with the timing of ecosystem changes in shelf seas, important for fisheries and ecosystem services, and melting of sea-ice.