Résumé
We show, from recent data obtained at specimen North Pacific
stations, that the fossil fuel CO2 signal is strongly
present in the upper 400 m, and that we may consider areal
extrapolations from geochemical surveys to determine the magnitude of
ocean fossil fuel CO2 uptake. The debate surrounding this
topic is illustrated by contrasting reports which suggest, based upon
atmospheric observations and models, that the oceanic CO2
sink is small at these latitudes; or that the oceanic CO2
sink, based upon oceanic data and models, is large. The difference
between these two estimates is at least a factor of two. There are
contradictions arising from estimates based on surface partial
pressures of CO2 alone, where the signal sought is small
compared with regional and seasonal variability; and estimates of the
accumulated subsurface burden, which correlates well other oceanic
tracers. Ocean surface waters today contain about 45
μmol⋅kg−1 excess CO2 compared with
those of the preindustrial era, and the signal is rising rapidly. What
limits should we place on such calculations? The answer lies in the
scientific questions to be asked. Recovery of the fossil fuel
CO2 contamination signal from analysis of ocean water
masses is robust enough to permit reasonable budget estimates. However,
because we do not have sufficient data from the preindustrial ocean,
the estimation of the required Redfield oxidation ratio in the upper
several hundred meters is already blurred by the very fossil fuel
CO2 signal we seek to resolve.