Picture (above): Wind off Cape Terawhiti. Credit Phil Norton. (Creative Commons license – Flickr)

The transport of surface waters into the ocean interior (“ventilation”) plays a critical role in the uptake of heat, carbon, and nutrients.  This ventilation is, at least partially, controlled by the westerly winds blowing over the oceans. Over the past few decades in the mid-latitudes of the Southern Hemisphere, these winds have grown stronger and shifted poleward.  

CLEX researchers and colleagues examined the movement of surface water into the depths of the ocean in response to these wind changes using a global ocean model. Through this model, they calculated the mean time for transport of water from the surface to the ocean interior.

The results revealed considerable variation in this movement of water from the surface to the depths in response to changes in wind strength and the geographical shift of these winds towards Antarctica.

When the wind strength increased it took a shorter time for the surface waters to penetrate the mid-depths of the ocean.

However, the impact of the southward shift in wind location on the transport of water from the surface to mid-depths varied. South of 35oS it took less time for the surface water to shift to these depths. North of that latitude it took longer.

The research also shows that the increase in wind speed led to a corresponding increase in the volume of water that penetrated the upper and intermediate depths. In contrast, the poleward shift had essentially no change on the volume of water that shifted from the surface to the deep ocean. These results give researchers new insight into how the storage of anthropogenic carbon and heat in southern oceans may change. They suggest an increase in storage is likely with a strengthening of the winds, but the southward shift of these wind tracks will have far less impact on the capacity to store carbon and heat.

  • Paper: Darryn W. Waugh, Andrew McC. Hogg, Paul Spence, Matthew H. England, Thomas W.N. Haine. Response of Southern Ocean ventilation to changes in mid-latitude westerly winds. Journal of Climate32, 5345-5361. https://doi.org/10.1175/JCLI-D-19-0039.1