²³⁴Th-Derived Particle Fluxes and Seasonal Variability: When Is the SS Assumption Reliable? Insights From a Novel Approach for Carbon Flux Simulation

E. Ceballos-Romero , F. de Soto , F. A. C. Le Moigne (1) , R. García-Tenorio , M. Villa-Alfageme

1 MIO - Institut méditerranéen d'océanologie

²³⁴Th measurements are widely used to estimate the downward carbon flux of particles via the oceanic Biological Pump. Carbon export is evaluated from ²³⁴Th-²³⁸U disequilibrium assuming either steady state (SS) conditions, or including a non-SS (NSS) correction. We use a novel stochastic simulation to quantify the temporal variation of vertical carbon and ²³⁴Th (dissolved and particulate) concentration profiles with high temporal resolution. We calculate seasonal export as if in situ measured with sediment trap and SS- and NSS-²³⁴Th approaches and quantify the periods of validity for SS/NSS conditions defined in previous works. The SS approach is valid throughout the entire season in oligotrophic regions. In temperate regions, the SS introduces a bias in the export if sampling takes place outside specific temporal windows. Windows of validity range from days in short blooms of 15-day duration to weeks in blooms longer than 30 days.

Keywords: stochastic simulation; 234-thorium; steady state approach; non-steady state correction; transient regimes; seasonal POC flux

Domains: Sciences of the Universe [physics]; Sciences of the Universe [physics]; Earth Sciences

E. Ceballos-Romero, F. de Soto, F. A. C. Le Moigne, R. García-Tenorio, M. Villa-Alfageme. ²³⁴Th-Derived Particle Fluxes and Seasonal Variability: When Is the SS Assumption Reliable? Insights From a Novel Approach for Carbon Flux Simulation. Geophysical Research Letters, 2018, 45, pp.13,414-13,426. ⟨10.1029/2018GL079968⟩. ⟨insu-03635015⟩