Narrowing in on Southern Ocean eddies: Guest blog by NIWA staff writer Campbell Gardiner

Bottom water properties analysis

A new modeling tool developed as part of the Deep South National Science Challenge is revealing fresh insights into Southern Ocean eddies and their influence on global climate.    

Using the New Zealand Earth System Model (NZESM) as a starting point, Wellington-based NIWA ocean modeler Erik Behrens has developed a 'nested model' which can resolve mesoscale (intermediate-size) eddies in greater detail than ever before.  

Mesoscale eddies are an important part of the big picture of ocean modeling because they transport properties such as heat and nutrients around the ocean. The Southern Ocean is a hot-bed of eddie activity – especially in and around the Ross and Amundsen Seas.    

With traditional ocean modelling, the globe is divided into small rectangles – each measuring 1 degree (or 100km) across. The grids also have vertical levels to account for processes happening below the surface.   

Up until now, models like the NZESM haven't been able to explicitly model ocean eddies. But thanks to a technique called local grid refinement, Erik has obtained crystal clear resolution 1/15° (2–3km) over the Ross and Amundsen Seas.             

It's still early days for Erik's new nested model, with some test simulations having been run. Next steps are to validate the model and consider research opportunities afforded by the higher resolution.   

Researchers, for example, are expected to be able to use the new set-up to model surface properties in finer detail and better investigate bottom water changes such as temperature and salinity.  

Erik gave an overview of the new, nested grid model during a recent Deep South Challenge seminar. 

 A recording can be found at https://www.youtube.com/watch?v=JktkYpH0Scc.