Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions

Didier Swingedouw,Pablo Ortega,Eric Guilyardi,Roland Séférian,Valérie Masson-Delmotte,Paul G Butler,Myriam Khodri,Juliette Mignot

doi:10.1038/ncomms7545

Abstract

While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood. Here we show that the subset of CMIP5 historical climate simulations that produce such bidecadal variability exhibits a robust synchronization, with a maximum in Atlantic Meridional Overturning Circulation (AMOC) 15 years after the 1963 Agung eruption. The mechanisms at play involve salinity advection from the Arctic and explain the timing of Great Salinity Anomalies observed in the 1970s and the 1990s. Simulations, as well as Greenland and Iceland paleoclimate records, indicate that coherent bidecadal cycles were excited following five Agung-like volcanic eruptions of the last millennium. Climate simulations and a conceptual model reveal that destructive interference caused by the Pinatubo 1991 eruption may have damped the observed decreasing trend of the AMOC in the 2000s. Our results imply a long-lasting climatic impact and predictability following the next Agung-like eruption.

Highlights

While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood
We investigate the mechanisms involved in bidecadal North Atlantic and Atlantic Meridional Overturning Circulation (AMOC) variations and reduced AMOC variability around the trend during the 2000s using Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations and sensitivity tests conducted with the IPSL-CM5A-LR model[36]
Historical climate simulations (1870–2005) driven by natural and anthropogenic forcing archived in the CMIP5 database exhibit a large spread in the simulated AMOC at 48°N (Fig. 1a)

Summary

Introduction

While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood. Beyond direct information on AMOC, North Atlantic observations[14,15] and proxy records indicate a 20-year preferential variability in this region in the atmosphere[16], sea ice[17] and the ocean[18,19] Such variability can be associated with the dynamics of subpolar gyre, whose characteristic decadal timescales are associated with advection processes and the size of the gyre[20,21]. We evaluate the potential impact of moderate explosive volcanic eruptions (similar to Agung or Pinatubo) on the North Atlantic bidecadal preferential variability For this purpose, we use available outputs from different climate models using the Coupled Model Intercomparison Project Phase 5 (CMIP5) database[35] complemented by additional simulations performed using one model, and in situ recent oceanic observations as well as longer paleoclimate proxy records of the last millennium. We find that moderate volcanic eruptions may reset a 20-year intrinsic variability mode in the North Atlantic both in model simulations as well as in the data analyzed, leading to interference patterns over the recent period and in the near future

Methods

Results

Conclusion