title: Heat content variability in the North Atlantic Ocean in ocean reanalyses.
abstract: Warming of the North Atlantic Ocean from the 1950s to 2012 is analyzed on neutral density surfaces and vertical levels in the upper 2000 m. Three reanalyses and two observational data sets are compared. The net gain of 5 × 1022J in the upper 2000 m is roughly 30% of the global ocean warming over this period. Upper ocean heat content (OHC) is dominated in most regions by heat transport convergence without widespread changes in the potential temperature/salinity relation. The heat convergence is associated with sinking of midthermocline isopycnals, with maximum sinking occurring at potential densitiesσ0= 26.4-27.3, which contain subtropical mode waters. Water masses lighter thanσ0= 27.3 accumulate heat by increasing their volume, while heavier waters lose heat by decreasing their volume. Spatially, the OHC trend is nonuniform: the low latitudes, 0-30°N are warming steadily while large multidecadal variability occurs at latitudes 30-65°N.
  
  
  CONCLUSIONS
  Heat content change dominated by heat transport convergence Due to widespread sinking trend of midthermocline isopycnals over 50+ years.
authors.affiliation: NASA Goddard Space Flight Center Greenbelt, Maryland, USA.
authors.forename: Sirpa
authors.initials: S
authors.lastname: Häkkinen
authors.affiliation: University of Washington Seattle, Washington, USA.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Rhines
authors.affiliation: NASA Goddard Space Flight Center Greenbelt, Maryland, USA ; Wyle STE Group Houston, Texas, USA.
authors.forename: Denise L
authors.initials: DL
authors.lastname: Worthen
keywords: heat content