What Causes Recent Subpolar North Atlantic Ocean Temperature Extremes?

Abstract:

Mid-high latitude North Atlantic Ocean temperature anomalies have been observed on a range of timescales from interannual to centennial. In the past decade, a large region of persistently low subpolar surface temperatures and reduced ocean heat content was evident from winter 2013-14 to 2016. The presence of this feature at a time of pervasive warming elsewhere stimulated considerable debate and ongoing discussion. Here, I will revisit the role of air-sea interaction (including the influence of changing storm tracks) and ocean processes in generating this cold anomaly, place it in a longer-term context and discuss its subsequent evolution – in particular a recurrent surface intensified phase in 2018 and damping through to 2020. Results from a new combined analysis of the mixed layer heat budget using ocean heat content (EN4) observations and surface heat flux datasets (ERA5,NCEP/NCAR) will be presented that firmly establish intense winter heat loss as the major cause (65-70%) of the cold anomaly. In addition, the recent cold anomaly will be contrasted with strong interannual warming events in the 1990s and the mechanisms driving both classes of event will be discussed.