Modelling the triple-isotopic composition of dissolved oxygen using a 3D Earth System Model of intermediate complexity

Marine photosynthesis (or gross primary productivity, GPP) is one of the main mechanisms for carbon fixation and global oxygen formation, contributing around half of the oxygen produced on Earth and sustaining aquatic ecosystem. Understanding the mechanisms that regulate GPP is essential for gaining insights into biological oxygen and carbon cycles. The combined study of GPP with net primary productivity (NPP) and net community productivity (NCP) will greatly improve our understanding of the interactions between biological processes, linking photosynthesis, respiration and the carbon cycle.

The triple isotopic composition of dissolved oxygen has been proposed as a tracer of gross oxygen productivity in aquatic ecosystem (Luz & Barkan, 2000).  The reasoning behind this is that the ∆¹⁷O of dissolved O₂ is determined by two main end-members: the marine photosynthesis (∆¹⁷O ~ 249 ppm) and the atmospheric O₂ (∆¹⁷O ~ 8 ppm), as ∆¹⁷O is not much affected by other processes that fractionate oxygen in a mass-dependent manner. However, subsequent studies have highlighted potential sources of uncertainty or bias in this proxy. Uncertainties about fractionation factors and transport parameters call the tracer into question (Levine et al., 2009; Nicholson et al., 2014; Li et al., 2022).

To address this issue, we have recently implemented the triple isotopic composition (δ¹⁷O and δ¹⁸O) of dissolved O₂ into the 3D Earth System Model of intermediate complexity, iLOVECLIM. We will present our preliminary results of model comparing them with observation and discussing sensitivity experiments; we further compare our results to previous findings that used 1D or 2D modeling approaches.