Including the triple isotopic composition of dissolved oxygen in the ocean into the iLOVECLIM model (version 1.1.7): development and evaluation

Contributing around half of the oxygen produced on Earth, marine photosynthetic production is one of the main mechanisms for carbon fixation, with a central role in the oxygen cycle. The triple isotopic composition of atmospheric oxygen ( ¹⁷ Δ), measured in ice cores, provides a global integrator of past biospheric oxygen fluxes, which can also provide indirect constraints on associated carbon-cycle processes. However, deconvolving the signal of ¹⁷ Δ requires one to isolate the contribution of oceanic biosphere productivity ( ¹⁷ Δ _ocean ) from those of the terrestrial biosphere ( ¹⁷ Δ _terr ) and the stratosphere ( ¹⁷ Δ _strato ). Here, we present the first implementation of ¹⁷ Δ _ocean in the intermediate-complexity climate model iLOVECLIM. The three main processes controlling ¹⁷ Δ _ocean , i.e. photosynthesis, respiration, and air–sea gas exchange, are explicitly represented and evaluated under preindustrial conditions. Model results show overall good agreement with available measurements, particularly in the Pacific Ocean. In contrast, systematic overestimation is found in the Southern Ocean. At fixed stations, seasonality is reproduced but with underestimated amplitude. These discrepancies mainly reflect challenges in representing remineralization and oxygen minimum zones, and highlight opportunities to refine the representation of primary productivity and vertical mixing. Overall, this new implementation provides the first coupled model framework for simulating ¹⁷ Δ _ocean , both as a diagnostic of biogeochemical processes and as a tool for reconstructing past changes in marine productivity. Extending the implementation to the terrestrial biosphere will further allow reconstruction of the past global biosphere and direct comparison with ¹⁷ Δ records from ice cores.