Application of a Newton-Krylov Solver to Spin-up Biogeochemical Tracers

A challenge for ocean biogeochemical modeling is spinning up the
tracers to be in balance with the model's circulation. This spinup
is desirable for clean comparison of the modeled solution to
observations, such as nutrient distributions, and for initializing
transient experiments, such as those done with coupled climate
carbon models. Two aspects of the challenge are the long time scales
of ocean ventilation and the short time scales of processes in the
upper ocean. We present results obtained using a preconditioned
Newton-Krylov solver to generate equilibrium solutions for online
biogeochemical tracers that are coupled to an ecosystem model. A
novel aspect that is used is to partially decouple the ecosystem
tracers from geochemical tracers, which eliminates some non-linear
feedbacks that destabilize convergence and ease the inversion of
the preconditioner.