P1010045 Jana Newman

Antarctica is an interface of ice, ocean and atmosphere. Photo: Jana Newman

Case study: First fully coupled ocean-atmosphere model for the Ross Sea

21 July 2023

A new modelling tool developed by Antarctic Science Platform researchers accurately represents ocean-atmosphere-sea ice interactions in the Ross Sea, which is critical for reducing uncertainty in the assessment of future climate scenarios.

At Antarctica’s coastal margins, glacial ice, ocean, atmosphere and sea ice come together. This interface, where components of the Earth system meet, is an important and complex driver in moderating regional and global climate systems. However, this carefully balanced interface is shifting in response to a warming climate.

Accurate representation of ice-ocean-atmosphere interactions and feedbacks is crucial to our understanding of:

  • the present state of the Southern Ocean and Antarctic continent
  • the sensitivity to change in the interconnected Earth system components
  • how the system might change under different conditions.
ANZSC2262 3 Tim Higham

At Antarctica’s coastal margins, glacial ice, the ocean, atmosphere and sea ice come together. Photo: Tim Higham

To understand how oceanic and atmospheric processes interact with the cryosphere (ice features) in the Ross Sea region, we need high spatial resolution and accurate representation of local conditions. However, the challenges of Antarctic research mean that observational data is sparse both spatially and temporally, and we look to numerical models to represent observed behaviours, simulate Earth system interactions, and project future trends. Ideally, the models integrate individual components (e.g. atmosphere, ocean and ice) and allow them to interact with each other, in the form of fully coupled models.

At a large scale, Earth system models have coupled global ocean, atmosphere, land and sea ice models, but the spatial resolution is low and the physics (the representation of physical processes and interactions) are not optimised for polar areas. Global models, for example, struggle to capture observed sea ice behaviour, and often misrepresent the temperature and freshness of the Southern Ocean.

Conversely, regional climate models offer higher resolution and better capture local conditions, but rarely fully couple ocean-atmosphere-ice dynamics. This means regional models are typically used in standalone mode, and poorly reflect the physics and potential interactions and feedbacks between the different Earth system components.

Through Antarctic Science Platform research and the National Modelling Hub, we have developed the first regional scale coupled ice shelf-ocean-sea ice-atmosphere model for the Ross Sea, specifically created to capture the interactions between atmosphere, ocean and ice at relevant spatial scales (read this recent publication for more information).

The Ross Sea is a location where modelling accuracy is important, because relatively small-scale features have a significant effect on the global ocean circulation, heat distribution and carbon cycle.

Model area map

Antarctic map showing the Ross Sea and surrounding area that the new coupled model represents. Source: Malyarenko et al, 2023

The new coupled model has been used to examine open water, sea ice cover and ice sheet interfaces, and was found to be the ideal tool to obtain the most accurate representation of ocean-atmosphere-sea ice interactions for polar climates. This model makes conservation of heat and mass possible over long-term simulations, which is essential for more reliable future projections.

Having access to a coupled model for the Ross Sea is critical for optimising sea ice modelling, and for assessing atmospheric forcing on sea ice, as well as regional scale ocean circulation sensitivity to reduced sea-ice scenarios. Understanding small-scale features like polynyas, that have outsized impact on the global ocean circulation, is key to predicting changes. The successful implementation of this coupled model is a critical milestone in improving future global projections.

This Case Study was prepared as part of the Platform’s annual reporting to MBIE for the 2022-2023 year. It illustrates how uncertainty in future climate scenarios is reduced by better improved understanding of how oceanic and atmospheric processes interaction with the cryosphere.

Contributors: Alena Malyarenko, Alexandra Gossart