The coupled Southern Ocean-Sea ice-Ice shelf Model (SOSIM v1.0)
Motivation
The Southern Ocean, a critical region south of 60°S or the northern limit of the Antarctic Circumpolar Current (ACC), is highly susceptible to rapid climate change due to complex interactions within the coupled ocean-sea ice-air-ice sheet system. However, the seasonal dynamics of sea ice, combined with the region's harsh conditions and extreme remoteness, impose significant logistical challenges, resulting in a severe scarcity of in-situ observations. Compounding this, coarse-resolution global climate models, such as those in CMIP6, struggle to accurately represent the intricate interactions where the ocean, sea ice, and ice shelves meet, due to their inadequate resolution and incomplete physics. These limitations hinder our ability to predict future climate change, assess the stability of the Antarctic Ice Sheet, and project global sea-level rise accurately. Developing a high-resolution coupled model capable of explicitly resolving these critical processes is not merely an academic exercise but a pressing necessity for improving the fidelity of global climate projections.
So far, one of the primary challenges still lies in the representation of Antarctic ice shelves. The accelerated melting of Antarctic ice shelves, driven by the intrusion of warm ocean waters, is a major contributor to global sea-level rise. For instance, glaciers in the West Antarctic Peninsula are highly vulnerable to changes in ocean circulation that transport heat beneath the ice shelves. The potential collapse of such ice shelves could lead to substantial ice discharge from the Antarctic Ice Sheet, posing a severe threat to coastal communities worldwide. For China, with its vast and densely populated coastal regions, the implications are particularly profound. Research indicates that the rate of sea-level rise along the coast of China is already higher than the global average (https://www.nmdis.org.cn/c/2024-04-24/80878.shtml), and the current rate of sea-level rise along the southeastern coast of China is unprecedented over the past 4,000 years. This exacerbates risks of coastal inundation, saltwater intrusion into freshwater aquifers, increased severity of storm surges, and other coastal hazards, which threaten infrastructure, water security, and economic stability. Accurately projecting the contribution of the Antarctic Ice Sheet to sea-level rise is therefore crucial for formulating coastal adaptation and mitigation strategies in China.
To improve our understanding of the complex Antarctic climate system, the development of the Southern Ocean-Sea Ice-Ice shelf Model (SOSIM) is a direct response to these challenges. By resolving the critical processes of warm water intrusion across the continental slope and the resulting basal melt, SOSIM provides a useful tool to study the contribution of the Antarctic Ice Sheet to future sea-level changes, which is essential for risk assessment and policy planning in China and globally. Beyond this, SOSIM offers several key advantages, including the ability to study cross-slope exchanges, understand sea ice variability, improve climate projections, and support operational forecasting.
Overall, the motivation for SOSIM is grounded in addressing critical gaps in our observing and modeling capabilities. It empowers scientists to better understand and predict the changes occurring in the Southern Ocean, particularly those leading to ice shelf melt and sea-level rise, thereby providing invaluable information for societal adaptation and the development of resilient coastal strategies.
Sea level rise due to melting of the Antarctic Ice Sheet
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The domain of SOSIM
Download Video (MP4)
Model configuration
SOSIM v1.0 is built upon the MITgcm (c66m version), integrating fully coupled ocean, dynamic-thermodynamic sea ice, and thermodynamic ice shelf components within a unified framework. In the MITgcm, the ocean, sea ice, and ice shelf components share the same horizontal grid layout (the Arakawa C-grid). The ocean component is based on the primitive equations with the Boussinesq approximation and hydrostatic assumption). The sea ice component is included to simulate the freeze-thaw cycles of dynamic and thermodynamically active sea ice, and the ice shelf component is introduced to represent static and thermodynamically active ice shelves. SOSIM is forced by the ERA5 reanalysis and initialized with oceanic climatology from WOA18 and velocity fields from ECCO2.
The model domain is placed on a square region centered on the South Pole. The model topography, including sub-ice-shelf cavities, is derived from the RTopo-2 dataset. For such a square box, the latitude covers the Southern Ocean from the South Pole to 35.7°S, with the latitude of the northern boundary ranging from ~35.7°S at corners to ~50.2°S at the inscribed circle. The horizontal grids employ an orthogonal curvilinear projection, with 1800 × 1800 horizontal grids. The grid spacing ranges from ~4 km at the northern boundary to ~5 km around the coast of Antarctica, with an average spacing of ~4.7 km. The vertical discretization of SOSIM has 70 levels, ranging from a 5 m interval in the upper layers to a 300 m interval at the deeper layers, with partial cells to improve the representation of the bedrock and the ice draft of ice shelves.
Animation 1. A side view of the model domain in a three-dimensional Earth.
The color shading shows the elevation of the solid earth in RTopo-2, and the white semi-transparent region shows the Antarctic Ice Sheet.
Download Animation (MP4)
Initial conditions of potential temperature and salinity are derived from WOA18. Initial conditions of velocity are derived from the climatology mean of ECCO2. Initial conditions of sea ice are derived from satellite observations provided by the Institute of Environmental Physics, University of Bremen.
Animation 2. The initial conditions derived from WOA18 and ECCO2.
(a) The initial condition of potential temperature (°C) derived from WOA18.
(b) The initial condition of salinity (psu) derived from WOA18.
(c) The logarithmic magnitude of initial condition of the velocity (m/s) derived from ECCO2.
Download (a) Initial Potential Temperature
Download (b) Initial Salinity
Download (c) Initial Velocity
Akin to the initial conditions, the oceanic open boundary conditions of SOSIM are also derived from WOA18 and ECCO2. The open boundary conditions of potential temperature and salinity are derived from the monthly climatology of WOA18, and the velocity is derived from the monthly climatology of ECCO2. Since the monthly climatology of WOA18 only provides data from 0 m to 1500 m depth, the data below 1500 m depth on the open boundary is fixed as the annual climatology of WOA18.
Figure 1. Schematic of open boundary conditions, showing the vertical slices of potential temperature, salinity, and velocity derived from WOA18 and ECCO2 monthly climatology.
SOSIM is forced by the ERA5 atmospheric product, with a temporal resolution of 1 hr and a horizontal resolution of ~31 km. Such a high spatial and temporal resolution of ERA5 is useful for the simulation of the high-frequency wind power input into the Southern Ocean, and it could also improve the representation of coastal polynyas. The atmospheric forcing dataset from ERA5 includes 10-m wind speed, 2-m specific humidity, 2-m air temperature, downward longwave radiation, downward shortwave radiation, and precipitation. The temporal coverage of ERA5 extends from January 1940 to near present day, with satellite observations assimilated from 1979 onward, and SOSIM uses 1979-2022 inclusive for the integration in the current version.
Animation 3. ERA5 atmospheric forcing variables used in SOSIM, including
10-m wind speed (Wind), 2-m specific humidity (Sp hu), 2-m air temperature (tmp2m), downward longwave radiation (DLW), downward shortwave radiation (DSW), and precipitation (Precip), respectively.
Download Wind
Download Sp hu
Download tmp2m
Download DLW
Download DSW
Download Precip
Simulation Showcase
Some simulated results of SOSIM in 2022, including the oceanic potential temperature, salinity, velocity, the sea ice, and the basal melt/freeze of ice shelves.
Animation 4. Simulated potential temperature in 2022:
(a) sea surface temperature (°C) and (b) bottom temperature (°C).
Download (a) Sea Surface Temperature
Download (b) Bottom Temperature
Animation 5. Simulated salinity in 2022:
(a) sea surface salinity (psu) and (b) bottom salinity (psu).
Download (a) Sea Surface Salinity
Download (b) Bottom Salinity
Animation 6. Simulated sea surface velocity magnitude and surface vortex Rossby number in 2022:
(a) sea surface velocity magnitude (m/s) and (b) surface vortex Rossby number.
Download (a) Surface Velocity Magnitude
Download (b) Surface Vortex Rossby Number
Animation 7. Simulated 3D oceanic fields in 2022:
(a) potential temperature (°C), (b) salinity (psu),
(c) potential density (kg/m3), and (d) the logarithmic magnitude of velocity (m/s).
Download (a) 3D Potential Temperature
Download (b) 3D Salinity
Download (c) 3D Potential Density
Download (d) 3D Velocity
Animation 8. The simulated sea ice concentration/thickness and velocity magnitude in 2022:
(a) sea ice concentration, with shadow to show the sea ice thickness and
(b) the magnitude of sea ice velocity (m/s).
Download (a) Sea Ice Concentration/Thickness
Download (b) Sea Ice Velocity
Animation 9. The simulated basal melt/freeze rate of ice shelves in 2022:
(a) spatial distribution of Antarctic Ice Sheet, with semitransparent region denoting ice shelves, and
(b) the basal melt/freeze rate (m/yr) of ice shelves.
Download (a) Ice Shelf Distribution
Download (b) Basal Melt/Freeze Rate
Data access
The model configuration and simulation data (1979-2022) are publicly available, including:
- Model source code, initial conditions and open boundary conditions
- Daily outputs (binary format) for the state estimate of the ocean, sea ice, and ice shelves
- Monthly climatology and Grid configuration (netcdf4 format)
- A sample code (Matlab scripts) for reading and visualizing 2D and 3D fields from daily output data
SOSIM is distributed by the Data Center of the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), with the DOI:10.12378/geodb.2025.2.117.V1. Please access the data by using the following FTP Server:
- host: www.hellosea.org.cn
- port: 60022
- username: SOSIM
- password: Sml123456
Please try to limit simultaneous accesses to one or two, in order to leave bandwidth for other users.
If the FTP protocol is not supported by your web browser, please use a FTP client such as WinSCP, FileZilla, and Flashfxp.
How to cite and acknowledge SOSIM
If you use the SOSIM datasets for a publication, please add the following sentence in the Acknowledgement part:
The SOSIM was made freely available and distributed by the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) and the SOSIM project that contribute to it. (https://www.sml-zhuhai.cn/).
Also please cite the following paper when you use the SOSIM dataset in your published work:
Liu et al., The coupled Southern Ocean-Sea ice-Ice shelf Model (SOSIM v1.0): configuration and evaluation. in prep
Contact information
For questions or cooperation inquiries, please contact us via:
Email: liuchengyan@sml-zhuhai.cn