Add ammonia oxidising archaea and N2O to WOMBATmid

[pearseb]

We aim to add nitrous oxide (N₂O) as a new tracer in WOMBAT-mid, including air–sea gas exchange.

During this process we update the Schmidt number calculations for O₂ and CO₂ following Wanninkhof (2014).

N₂O is produced by ammonia-oxidizing archaea (AOA) and a bacterial type that reduces NO3, consumed by another bacterial type, and AOA production of N2O is parameterized with yields from Frey et al. (2023, L&O). AOA have been made fully interactive with biomass-weighted NH₄⁺→NO₃⁻ oxidation. The two bacterial groups (Bac1 and Bac2) and AOA are grazed by both micro- and mesozooplankton. Zooplankton excretion has been updated to partition a fraction to DOM and the remainder to inorganic nutrients (default 20/80 split). These changes improve the model’s representation of microbial interactions and explicitly incorporate N₂O cycling, enabling evaluation of nitrogen–climate feedbacks.