The non-steady state oceanic CO2 signal: its importance, magnitude and a novel way to detect it

[摘要] The role of the ocean has been pivotal in modulating rising atmosphericCO₂ levels since the industrial revolution, sequestering nearly half ofall fossil-fuel derived CO₂ emissions. Net oceanic uptake of CO₂has roughly doubled between the 1960s (~1 Pg C yr⁻¹) and 2000s(~2 Pg C yr⁻¹), with expectations that it will continue toabsorb even more CO₂ with rising future atmospheric CO₂ levels.However, recent CO₂ observational analyses along with numerous modelpredictions suggest the rate of oceanic CO₂ uptake is already slowing,largely as a result of a natural decadal-scale outgassing signal. This recentCO₂ outgassing signal represents a significant shift in ourunderstanding of the oceans role in modulating atmospheric CO₂. Currenttracer-based estimates for the ocean storage of anthropogenic CO₂ assumethe ocean circulation and biology is in steady state, thereby missing the newand potentially important "non-steady state" CO₂ outgassing signal. Bycombining data-based techniques that assume the ocean is in a steady state,with techniques that constrain the net oceanic CO₂ uptake signal, weshow how to extract the non-steady state CO₂ signal from observations.Over the entire industrial era, the non-steady state CO₂ outgassingsignal (~13 ± 10 Pg C) is estimated to represent about 9%of the total net CO₂ inventory change (~142 Pg C). However,between 1989 and 2007, the non-steady state CO₂ outgassing signal(~6.3 Pg C) has likely increased to be ~18% of netoceanic CO₂ storage over that period (~36 Pg C). The presentuncertainty of our data-based techniques for oceanic CO₂ uptake limitour capacity to quantify the non-steady state CO₂ signal, however withmore data and better certainty estimates across a range of diverse methods,this important and growing CO₂ signal could be better constrained in thefuture.

[学科分类] 地球化学与岩石