Global ocean modelling in the Deep South Challenge

This seminar with Erik Behrens (NIWA) describes results on the recent NZ marine heat wave, demonstrating that subsurface heat transport plays an important role in the years-to-decades occurrence of marine heat waves in the Tasman Sea

The oceans are the largest ecosystem on our planet, with complex physical and bio-geochemical interaction between the atmosphere, sea ice and ice shelves. Oceans are the main storage for human-produced heat and carbon. At the same, oceans have the ability to redistribute heat and carbon both across large distances and over time, which makes them the key component in the climate system. 

Our understanding of the oceans has improved substantially in recent decades, thanks largely to satellite and Argo observations (a global network of ocean floats). Models are still (and will always be) necessary to fill data gaps, to put observations into a larger spatial and temporal context, and to forecast future changes. 

The ocean model in our New Zealand Earth System Model (NZESM) is based on the NEMO and MEDUSA models, and can be used to model past, present and future conditions. 

This presentation includes a brief introduction into the NEMO model and to the model configuration (eORCA1) which is used in NZESM. It will also focus on recent NEMO applications and scientific research using nesting (grid refinement) techniques within NEMO. Within the Deep South Challenge, a new model has been developed which uses nests to obtain a 1/15° resolution over the Ross and Amundsen Seas. In this way we can investigate how model resolution influences the spreading of Antarctic Bottom Water from these regions.

Finally, we present results on the recent NZ marine heat wave, demonstrating that subsurface heat transport plays an important role in the years-to-decades occurrence of marine heat waves in the Tasman Sea.