We submitted a manuscript on the air-sea CO2 exchange timescale and efficiency, showing an interesting finding. High latitude waters are likely less equilibrated with the atmospheric CO2. This is not obvious because high latitude oceans are more windy and the local rate of gas transfer may be more efficient. However, this effect is cancelled out by the deep mixed layer at high latitudes. In fact, the effect of deep mixed layer overwhelms the gas transfer rate.
We then compare the observationally-derived air-sea gas exchange timescale with a model-derived surface residence time and a data-derived horizontal transport timescale, which allows us to define two non-dimensional metrics of gas exchange efficiency. These parameters highlight the Southern Ocean, equatorial Pacific, and North Atlantic as regions of inefficient air-sea equilibration where carbon anomalies are likely to form and persist. The efficiency parameters presented here can serve as simple tools for understanding regional air-sea disequilibrium in both observations and models.