The loss of oxygen from the ocean due to warming is not ubiquitous. In the Atlantic Ocean there has been no oxygen loss or gain in the subtropics over the past six decades (top 1 km, see Figure). Hogikyan and co-authors show that the amplification of the hydrological cycle, a response to climate change that results in a ‘salty-get-saltier, fresh-get-fresher’ sea surface salinity pattern, introduces a spatial pattern in the rate of climate change-driven oxygen loss. A salinification enhances ventilation of (already salty) mode waters that outcrop in the subtropics and opposes warming-driven oxygen loss, while a freshening reduces ventilation of (already fresh) deep waters that outcrop at subpolar latitudes and accelerates oxygen loss. Climate change introduces patterns of oxygenation through surface salinity changes, key to understanding observed and future regional changes.
Observed change in average oxygen concentration in the upper 1,000 m in the Atlantic Ocean from the Ito et al. observation-based product22 (1950–2016 period). Stippling indicates where at least one depth level (out of 47) has fewer than 20 years of data from which to estimate the trend. Hogikyan and co-authors attribute the so far unexplained oxygen gain in subtropical regions (in red) to increased ventilation by ‘salty-get-saltier' waters.