Observing and Modeling the Atlantic Meridional Overturning Circulation

Continuous direct measurement of the Atlantic Meridional Overturning Circulation (AMOC) around the globe is placing new constraints on ocean model simulations. These observation efforts include decadelong research in the subtropical North Atlantic at 26.5°N (Rapid Climate Change—Will the Atlantic Thermohaline Circulation Halt Meridional Overturning Circulation and Heatflux Array (RAPID-WATCH/MOCHA)), the 5-year effort in the South Atlantic near 30°S (South Atlantic Meridional Overturning Circulation (SAMOC)), and new observational deployments in the subpolar North Atlantic (Overturning in the Subpolar North Atlantic Program (OSNAP)). Advances in ocean modeling, the Coupled Model Intercomparison Project 5 (CMIP5) archive of climate model output, and numerous state estimation products now allow increased examination of processes that affect variability in AMOC and associated climate changes in the Atlantic Ocean. Moreover, the need for using knowledge of the state of the Atlantic Ocean to enable decadal climate prediction brings additional motivation to improve our understanding of AMOC.

The U.S. AMOC Science Team, comprising scientists from about 50 AMOC research projects, met in September in Seattle, Wash., to share findings and foster integration of observations and models to accelerate progress in understanding AMOC and its impacts. The meeting focused on four objectives: (1) evaluation and implementation of observational efforts, (2) estimates of AMOC state, variability, and change, (3) understanding mechanisms of variability and the potential for predictability of AMOC, and (4) the impact of AMOC changes on climate, cryosphere, regional sea level, ocean carbon biogeochemistry, and marine ecosystems.

As an emergent property of ocean dynamics, observations of AMOC provide essential metrics for evaluating ocean-only and coupled models as well as ocean reanalysis. There is little agreement in the representation of AMOC among different ocean reanalyses and with the 26.5°N observational time series. To make progress, it is important that error estimates accompany the time series of observational AMOC estimates and that adjustments in model variables be provided with reanalysis products to allow a more comprehensive comparison between models and observations.

Participants acknowledged the need for continuous and extended AMOC observations throughout the Atlantic Basin. Improved communication among observing system groups, among the modelers, and between the observationalists and modelers can help develop integrated, coherent evaluation of AMOC and the associated heat transport state, variability, and change, with continued focus on linkages between the South Atlantic and the Southern Ocean and between the North Atlantic and the Arctic. To sustain observations over the long term within budgetary constraints, investigations are needed to evaluate the potential for both existing and emerging technologies (e.g., deep Argo, gliders) to provide cost-effective approaches for monitoring AMOC.

Evaluating the role of AMOC in climate variability and change, including the rate of warming, connections to tropical cyclone activity, and shifts in tropical precipitation patterns, continues to be a focus. Research on how AMOC variations can affect changes in land and sea ice, regional sea level, ocean carbon uptake, and ecosystem dynamics is also important. Better coordination with other research communities (e.g., cryosphere, coastal ocean, ocean carbon biogeochemistry) is needed to accelerate understanding of the impacts of AMOC variability and change on the Earth system.

The U.S. AMOC Program is an interagency program organized within the U.S. Climate Variability and Predictability program, with projects funded by NASA, the National Oceanic and Atmospheric Administration, the National Science Foundation, and the Department of Energy. The U.S. program coordinates closely with the UK RAPID program. Further details can be found on the meeting website.

—LuAnne Thompson, School of Oceanography, University of Washington, Seattle; email: [email protected]; Gokhan Danabasoglu, National Center for Atmospheric Research, Boulder, Colo.; and Michael Patterson, U.S. Climate Variability and Predictability Project Office, Washington, D. C.

Citation: Thompson, L., G. Danabasoglu, and M. Patterson (2015), Observing and modeling the Atlantic Meridional Overturning Circulation, Eos, 96, doi:10.1029/2015EO026371. Published on 19 March 2015.

© 2015. American Geophysical Union. All rights reserved.

© 2015. American Geophysical Union. All rights reserved.