Ventilation

The figure below shows an annual cycle of oxygen changes in different isopycnal layers that are due to ventilation. This is calculated as the oxygen concentration change from time t1 to t2 in the corresponding isopycnal layer, multiplied by the mean layer thickness for the two time steps, i.e.

(O2(t2)-O2(t1)*(H(t2)+H(t1))/2

This calculations removes the dominant signal of layer thickness changes on the oxygen inventory, focusing on the part of the signal that is due to oxygen uptake from the atmosphere. The figure below shows monthly changes; with, black contours showing the surface outcrop of the layer. There is a strong increase during winter near the surface outcrop, suggesting an increase due to uptake from the atmosphere, and a decrease during summer when the layer is shut off from contact with the atmosphere, likely due to physical transport of ventilated water away from the formation region.