Trends and drivers in global surface ocean pH over the past 3 decades

[摘要] We report global long-term trends in surface ocean pH using a new pH dataset computed by combining fCO₂ observations from the Surface OceanCO₂ Atlas (SOCAT) version 2 with surface alkalinity estimates based ontemperature and salinity. Trends were determined over the periods 1981–2011and 1991–2011 for a set of 17 biomes using a weighted linear least squaresmethod. We observe significant decreases in surface ocean pH in~70% of all biomes and a mean rate of decrease of0.0018 ± 0.0004 yr⁻¹ for 1991–2011. We are not able to calculate aglobal trend for 1981–2011 because too few biomes have enough data for this.In half the biomes, the rate of change is commensurate with the trendsexpected based on the assumption that the surface ocean pH change is onlydriven by the surface ocean CO₂ chemistry remaining in a transientequilibrium with the increase in atmospheric CO₂. In the remainingbiomes, deviations from such equilibrium may reflect that the trend ofsurface ocean fCO₂ is not equal to that of the atmosphere, most notablyin the equatorial Pacific Ocean, or may reflect changes in the oceanic buffer (Revelle)factor. We conclude that well-planned and long-term sustained observationalnetworks are key to reliably document the ongoing and future changes inocean carbon chemistry due to anthropogenic forcing.

[学科分类] 地球化学与岩石