Detecting an external influence on recent changes in oceanic oxygen using an optimal fingerprinting method

[摘要] Ocean deoxygenation has been observed in all major ocean basins over the past50 yr. Although this signal is largely consistent with oxygen changesexpected from anthropogenic climate change, the contribution of externalforcing to recent deoxygenation trends relative to natural internalvariability is yet to be established. Here we conduct a formal optimalfingerprinting analysis to investigate if external forcing has had adetectable influence on observed dissolved oxygen concentration ([O₂])changes between ∼1970 and ∼1992 using simulations from twoEarth System Models (MPI-ESM-LR and HadGEM2-ES). We detect a response toexternal forcing at a 90% confidence level and find that observed[O₂] changes are inconsistent with internal variability as simulated bymodels. This result is robust in the global ocean for depth-averaged (1-D)zonal mean patterns of [O₂] change in both models. Further analysis withthe MPI-ESM-LR model shows similar positive detection results fordepth-resolved (2-D) zonal mean [O₂] changes globally and for thePacific Ocean individually. Observed oxygen changes in the Atlantic Ocean areindistinguishable from natural internal variability. Simulations from bothmodels consistently underestimate the amplitude of historical [O₂]changes in response to external forcing, suggesting that model projectionsfor future ocean deoxygenation may also be underestimated.

[学科分类] 地球化学与岩石