Ocean Carbon Uptake and Productivity in The CMIP6 Ensemble
The invasion of anthropogenic carbon and heat into the upper ocean is expected to continue into the 21st century, raising major concerns for the health of marine ecosystems and sustainability of global fisheries. Past CMIP5 assessments (e.g. Bopp et al. 2013) identified clear trends in upper ocean warming and acidification across models and scenarios, but outlined divergent responses for net primary productivity (NPP) and thermocline oxygen in several productive and biodiverse regions of the world ocean.
Proposed Hacking & Questions:
This project will examine historical simulations and future projections of ocean carbon and heat uptake and storage in the CMIP6 ensemble, and explore their impacts on marine ecosystems drivers, with a focus on primary productivity. Hacking will explore:
How do models simulate carbon and heat uptake compared to available observations? What are future projections under different ssp’s? what regions dominate carbon and heat uptake vs. storage? What are differences across models (uptake rates, regional differences, etc.) and what processes might explain these differences?
How well do models simulate the mean distribution and long-term trends of ecosystem drivers (SST, pH/aragonite saturation depth, [O2]/hypoxic depth, NPP) compared to available observations? Can we identify persistent or new biases since CMIP5? What are CMIP6 projections for marine ecosystem drivers in a warming climate? What are spatial characteristics, timescales of emergence, and differences across models? Is there a relationship between models’ carbon and heat uptake efficiency and the severity of their projected impacts on these ecosystem drivers? How did increased climate sensitivity since CMIP5 in certain models (e.g. CESM2) influence these impacts in these models?
Projections of NPP especially showcase major differences across CMIP5 models in sign and amplitude over important ocean regions (Eastern/central tropical Pacific, Subpolar gyres, etc. Fig 5. Bopp et al 2013). Does this spread still exist in CMIP6? Do projected changes in carbon export at depth mirror the changes in NPP? What physical and biogeochemical processes explain NPP and carbon export changes across regions and models (e.g. changes in easterlies, upwelling, nutrient transport by the EUC or the overturning circulation, stratification and ventilation, remineralization rates, etc.)?
We will prioritize developing efficient workflows for loading, analysis, and plotting of model outputs and comparison to observations, and aim for process-based examination of model projections, inter-model differences, and model biases.
Anticipated Data Needs
Monthly (for season-sensitive processes/variables) and/or annual ocean physical and biogeochemical variables from the piControl, Historical, and main ssp experiments.
Anticipated Software Tools
We will primarily rely on Xarray/Dask for analysis, matplotlib/cartopy for visualization, and explore additional tools (ESMintake, ESMlab, xgcm) as needed.
Ocean BGC enthusiasts; Python beginners and experts are all welcome. The proposed hacking and guiding questions (1-3) are made broad enough to serve as starting points for team members to focus on or spawn off/lead as a sub-project with more specific (or different?) questions that hopefully will still fall under the broad theme of carbon cycling and ecosystem drivers in the CMIP6. Inter-projects synergies and exchange of expertise are encouraged.