Anomaly of heat content in the northern Atlantic in the last 7 years: Is the ocean warming or cooling?

Whether the North Atlantic Ocean is warming or cooling is an important question both in physical oceanography and climate change. The Argo profiling buoys provide an accurate and stable instrument for determining the tendencies in heat content from the surface to 2000 m from 1999 to 2005. To calculate temperature and heat content anomalies two reference climatologies are used. These are the well known WOA2001 climatology (Stephens et al., 2002), and a new WOCE Global Hydrographic climatology (Gouretski and Koltermann, 2004). The former climatology is used for our main results, and the latter is used for evaluating the sensitivity of our results to the climatology. Our scheme allows us to estimate the anomaly of heat content (AHC) in the North Atlantic and its smaller sub-domains (i.e. 10° boxes) for the period 1999–2005. We have found a dipole structure in the time averaged AHC: negative values are concentrated in the southern and middle latitudes of the North Atlantic whilst positive values are found north of 50°N. The upper 1500 m of the North Atlantic is warming throughout the period 1999 to 2005.