Abstract. Ocean circulation and the marine carbon cycle can be
indirectly inferred from stable and radiogenic carbon isotope ratios
(δ13C and Δ14C, respectively), measured directly
in the water column, or recorded in geological archives such as sedimentary
microfossils and corals. However, interpreting these records is non-trivial
because they reflect a complex interplay between physical and biogeochemical
processes. By directly simulating multiple isotopic tracer fields within
numerical models, we can improve our understanding of the processes that
control large-scale isotope distributions and interpolate the spatiotemporal
gaps in both modern and palaeo datasets. We have added the stable isotope
13C to the ocean component of the FAMOUS coupled atmosphere–ocean
general circulation model, which is a valuable tool for simulating complex
feedbacks between different Earth system processes on decadal to
multi-millennial timescales. We tested three different biological
fractionation parameterisations to account for the uncertainty associated
with equilibrium fractionation during photosynthesis and used sensitivity
experiments to quantify the effects of fractionation during air–sea gas
exchange and primary productivity on the simulated δ13CDIC
distributions. Following a 10 000-year pre-industrial spin-up, we simulated
the Suess effect (the isotopic imprint of anthropogenic fossil fuel burning)
to assess the performance of the model in replicating modern observations.
Our implementation captures the large-scale structure and range of δ13CDIC observations in the surface ocean, but the simulated
values are too high at all depths, which we infer is due to biases in the
biological pump. In the first instance, the new 13C tracer will
therefore be useful for recalibrating both the physical and biogeochemical
components of FAMOUS.
Supplementary material to "CM2Mc-LPJmL v1.0: Biophysical coupling of a process-based
dynamic vegetation model with managed land to a general
circulation model"
