Climatology and annual cycle of global ocean dissolved oxygen represented by multiple observational gridded products

Abstract. Ocean dissolved oxygen (O₂) is an essential climate variable crucial for sustaining the marine life; thus, changes of O₂ at various spatiotemporal scales should be quantified and understood. Here, we study the climatology and annual cycle of O₂ at regional to global scales using eight available gridded observational products. These datasets are generated by different groups using different primary data selection, quality control, bias correction and interpolation methods including statistical and machine-learning based mapping methods. A common set of metrics was collaboratively developed by the community of Gridded Observational Dataset Intercomparison Project-Dissolved Oxygen (GODIP-DO) to facilitate the inter-comparison, which allows assessing the robustness of the uncertainties through the spread of the products. Global mean O₂ profiles are consistent among all products (±3 µmol kg^-1), with the well-established decrease from high surface values to a minimum ~1000 meters, and subsequent increase to higher O₂ at depth, although local differences could reach ±25 µmol kg^-1 (0–1000 m). The hemispheric O₂ annual cycle correlates strongly with ocean temperature changes, suggesting the key driver of temperature for the O₂ annual cycle. However, there is substantial variation in the global mean 0–100 m O₂ annual cycle, the magnitude ranges from -1 to 0.8 μmol kg^-1, with a standard deviation of the datasets of ~0.3 μmol kg^-1. Average oxygen minimum zones (OMZ) volume among the products is 80.92 × 10⁶ km³ (±1.95 %) for a 60 µmol kg^-1 threshold and 152.00 × 10⁶ km³ (±1.72 %) for a 90 µmol kg^-1 threshold. Our results serve as a starting point for resolving the uncertainty budget of the ocean O₂ changes.