Theory 020/Earth & Space /Oceanography
Ocean Heat Uptake Is an Eddy Problem
Uptake is modelled as a surface flux. The bottleneck may be how fast the interior mixes.
Ocean heat uptake is set by eddy diffusivity at a critical stratification rather than by surface warming, so uptake should slow abruptly once stratification passes a threshold.
01The evidence
Ocean heat uptake varies between decades in ways that surface forcing does not explain, and eddy diffusivity is known to depend on stratification.
02The tension
Models tune diffusivity as a constant and attribute variability to forcing. The observed pauses and surges are then poorly reproduced.
03The mechanism
Heat entering the surface must be carried into the interior by eddies and mixing. The efficiency of that transport falls as stratification strengthens, because the same energy lifts less dense water a shorter distance.
That makes uptake a function of stratification, with a threshold where eddy transport saturates and further heating stays near the surface.
04What this is not
Forced models tune diffusion. This makes diffusion a function of stratification, which predicts abrupt slowdowns.
05Predictions
- P1Uptake should slow when stratification crosses a threshold.
- P2Decadal variability should track diffusivity changes.
- P3Heat should accumulate near the surface after the threshold.
06Refutation
Uptake tracking surface forcing at controlled stratification would restore the forced model.
07What it changes
It would change how ocean heat uptake is projected.