The US Ocean Carbon and Biogeochemistry (OCB) Program hosted a two-day workshop December 8-9, 2018 in Washington, DC on Ocean Carbon Uptake in CMIP6 Models: Synthesis and Intercomparison. The international Coupled Model Intercomparison Project (CMIP), now in its 6th incarnation, is generating a wealth of new global numerical simulations that will be available as a resource to the oceanographic community. The coupled simulations, integrating ocean-atmosphere-land dynamics, as well as ocean physics and biogeochemistry, span both the historical period (1850-present) and future scenarios out to 2100 and beyond. The goals of this workshop were to discuss:

1. high-profile CMIP5 Ocean Carbon Uptake analyses, challenges, and the planned suite of CMIP6 experiments;
2. new observational constraints, including GLODAPv2, SOCAT, SOCCOM, GO-SHIP, community observational synthesis efforts such as Obs4MIPs, ocean carbon inversions, and atmospheric observations of CO2 and oxygen;
3. updated model formulations and preliminary analysis of simulated regional and global patterns in heat/carbon/tracer uptake in CMIP6 experiments;
4. mechanisms underlying heat/carbon/tracer uptake differences across models and observations towards linking physical and biogeochemical drivers and their impact; and
5. tools and techniques that can lower barriers to analysis.

Participants highlighted the availability of several new decadal-scale synthesis products on air-sea CO2 flux and ocean carbon storage and the urgent need within the OCB community for more comprehensive and efficient computational tools to make optimal use of ‘big data’ resources such as the CMIP6 model archive. Additionally, the group emphasized that the timeline of CMIP6 model analysis is extremely tight: Modeling centers are planning to supply their data publicly in March-June 2019, and the manuscript submission deadline for contribution to the sixth assessment of the Intergovernmental Panel on Climate Change is Dec 31, 2019.  Workshop participants made several recommendations to facilitate and coordinate community use of the CMIP6 model archive:

• standardize tools for the estimation of ocean biomes
• explicitly separate river/coastal factors from open-ocean syntheses for air-sea CO2 flux and ocean storage
• incorporate pre-1850 carbon cycle changes
• improve understanding of ocean carbon cycling under reversibility and sustainability scenarios

A full workshop report and information about community follow-on activities will be available in the next couple of months.