Southern Ocean bottom water and sea ice in CMIP6 models
This is a topic that Lettie Roach and I are proposing together at UW.
The circulation in the Southern Ocean is important for global climate, meridional overturning circulation, and stratification. Its capacity for heat uptake and its influence on global overturning make it an important driver for heat and carbon redistribution in the global ocean system. Climate models often poorly simulate bottom water formation in the Southern Ocean (see figure below), creating bottom water with densities that differ from climatology or getting the right amount of bottom water with the right properties for the wrong reasons. In the CMIP5 models, no models produced deep Antarctic water on the shelf and allowing it to spill over and convect, rather, models generate deep water through open ocean deep convection. Also, those models with strong sea ice seasonality have spurious deep convection (Huezé et al, 2013). Diagnosing the deep convection process and the bottom water formation in CMIP6 models is an important step in identifying models that can accurately simulate future Southern Ocean properties as well as future global climate changes.
The first goal of this project is to determine whether CMIP6 models form bottom water around Antarctica with properties and in quantities similar to observations as well as if they do it in the right way. The second goal is to determine whether deep convection impacts sea ice variability across models or vice versa and if there is an easily identifiable physical mechanism.
We hope to diagnose the Southern Ocean bottom water formation in CMIP6 models and the impact this formation has on overturning and transport in the region. We also hope to see whether there are links between bottom water formation and sea ice concentration and whether there are any mechanisms that link the two, perhaps through overturning or transport. The following proposed can serve as a guideline as to what we hope to build.
- Determine the water mass properties in the abyssal ocean around Antarctica
- Look at mixed layer depths in the Southern Ocean
- Calculate MLD like Huezé et al? https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/grl.50287
- Calculate residual mean overturning streamfunction in the Southern Ocean
- Look at ACC transport in the Southern Ocean
- Plot seasonal sea ice concentration
Anticipated Data Needs:
Variables: potential temperature (thetao), salinity (so), density (h_rho), velocity (uo and vo), mass transport (umo and vmo), eddy mass transport (uhGM and vhGM), mixed layer depth (mlotst), sea ice concentration (siconc), and sea ice thickness (sithick)
Experiments: piControl, historical
Anticipated Software Tools
Anyone at all interested in the circulation in the southern ocean, sea ice near Antarctica, bottom water formation would be welcome. Experience with pangeo, python and/or xarray is a plus.