On the Abruptness of Bølling–Allerød Warming

Previous observations and simulations suggest that an approximate 38–58C warming occurred at intermediate depths in theNorthAtlantic over severalmillennia duringHeinrich stadial 1 (HS1), which induces warm salty water (WSW) lying beneath surface cold freshwater. This arrangement eventually generates ocean convective available potential energy (OCAPE), themaximumpotential energy releasable by adiabatic vertical parcel rearrangements in an ocean column. The authors find that basin-scale OCAPE starts to appear in the NorthAtlantic (;67.58–73.58N) and builds up over decades at the end ofHS1with amagnitude of about 0.05 J kg. OCAPEprovides a key kinetic energy source for thermobaric cabbeling convection (TCC). Using a high-resolution TCC-resolved regional model, it is found that this decadal-scale accumulation of OCAPE ultimately overshoots its intrinsic threshold and is released abruptly (;1 month) into kinetic energy of TCC, with further intensification from cabbeling. TCC has convective plumes with approximately 0.2–1-km horizontal scales and large vertical displacements (;1km), which make TCC difficult to be resolved or parameterized by current general circulation models. The simulation herein indicates that these local TCC events are spread quickly throughout the OCAPE-contained basin by internal wave perturbations. Their convective plumes have large vertical velocities (;8–15 cms) and bring the WSW to the surface, causing an approximate 28C sea surface warming for the whole basin (;700 km) within a month. This exposes a huge heat reservoir to the atmosphere, which helps to explain the abrupt Bølling–Allerød warming.