Abstract

Year of emergence (YoE)is defined as the year when an environment and the organisms within begin to experience significant different conditions from the pre-industrial conditions (1770 C.E.). This study calculates the global surface ocean YoEs for pH, partial pressure of CO₂ (pCO₂) and aragonite saturation (Ω) from a recent calculated surface ocean carbonate chemistry data product. The data product is calculated from the Surface Ocean CO₂ Atlas version 6 (SOCATv6) with modeled pCO₂ changes in the global surface ocean from the ESM2M model. We find that pCO₂, pH and Ω generally emerged from preindustrial conditions in the open ocean by the year 1950, while these properties have still not yet emerged along many ocean margins. We also found that Ω had a significantly delayed YoE compared to pH and pCO₂. The delayed YoE for Ω is caused by its lasting sensitivity to temperature variability, which increases the natural variability experienced by organisms, and a partial cancellation of the long term acidification trend by the global warming. Together, YoEs presented here highlight that there are hotspots (open ocean) and coldspots (ocean margins that were impacted by boundary currents) for the emergence of anthropogenic signals. Continuous data collection and synthesis are needed to further examine the impact of ocean acidification on ecosystem health.