Changes in the North Atlantic Oscillation influence CO₂ uptake in the North Atlantic over the past 2 decades

Helmuth Thomas (1) , A. E. Friederike Prowe , Ivan D. Lima , Scott C. Doney , Rik H. Wanninkhof , Richard J. Greatbatch , Ute Schuster , Antoine Corbière (2)

1 DO - Department of Oceanography [Halifax]
2 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques

Observational studies report a rapid decline of ocean CO₂ uptake in the temperate North Atlantic during the last decade. We analyze these findings using ocean physical-biological numerical simulations forced with interannually varying atmospheric conditions for the period 1979-2004. In the simulations, surface ocean water mass properties and CO₂ system variables exhibit substantial multiannual variability on sub-basin scales in response to wind-driven reorganization in ocean circulation and surface warming/cooling. The simulated temporal evolution of the ocean CO₂ system is broadly consistent with reported observational trends and is influenced substantially by the phase of the North Atlantic Oscillation (NAO). Many of the observational estimates cover a period after 1995 of mostly negative or weakly positive NAO conditions, which are characterized in the simulations by reduced North Atlantic Current transport of subtropical waters into the eastern basin and by a decline in CO₂ uptake. We suggest therefore that air-sea CO₂ uptake may rebound in the eastern temperate North Atlantic during future periods of more positive NAO, similar to the patterns found in our model for the sustained positive NAO period in the early 1990s. Thus, our analysis indicates that the recent rapid shifts in CO₂ flux reflect decadal perturbations superimposed on more gradual secular trends. The simulations highlight the need for long-term ocean carbon observations and modeling to fully resolve multiannual variability, which can obscure detection of the long-term changes associated with anthropogenic CO₂ uptake and climate change.

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]

Helmuth Thomas, A. E. Friederike Prowe, Ivan D. Lima, Scott C. Doney, Rik H. Wanninkhof, et al.. Changes in the North Atlantic Oscillation influence CO₂ uptake in the North Atlantic over the past 2 decades. Global Biogeochemical Cycles, 2008, 22, pp.4027. ⟨10.1029/2007GB003167⟩. ⟨hal-00770583⟩