Global surface ocean pH from 1770 to 2100
Abstract
Global surface ocean pH on the total hydrogen scale (pHT) from 1770 to 2100 is reconstructed or projected. The reconstruction is based on discrete measurements of carbonate data from the updated Global Ocean Data Analysis Project (GLODAPv2) data product, along with monthly climatologies for partial pressure carbon dioxide (pCO2) from the Lamont-Doherty Earth Observatory (LDEO) database and for sea surface temperature (SST) from the World Ocean Atlas (WOA). The projection is based on simulated temporal change rates in seawater pCO2 and SST from the Geophysical Fluid Dynamics Laboratory (GFDL)'s ESM2M model forced by the Intergovernmental Panel on Climate Change (IPCC)'s RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios. The results show that global surface ocean pHT in 2000 ranges from 8.0 to 8.2, with an area-averaged pHT of 8.1. Surface pH is controlled by SST through two processes: directly through the temperature dependence of the carbonate chemistry system; and indirectly through the temperature dependence of gas solubility which drives the air-sea gas exchange. They act in concert for aragonite saturation state, but oppose each other for pH. As a result, although aragonite saturation state is markedly lower in the colder polar regions than in the warmer tropical regions, surface ocean pH shows little latitudinal variation. Instead, the spatial variation of surface ocean pH is mainly attributable to air-sea CO2 disequilibria and equatorial upwelling activities. From 2000 to 2100, the globally and annually averaged surface ocean pH would decrease by an average 0.34 units (116% increase in hydrogen ion concentration) under the RCP8.5 scenario, and the surface ocean Revelle Factor would increase by an average 35%. For comparison, under the RCP4.5 scenario, the global surface ocean pH would decrease by only about 0.14 units (37% increase in hydrogen ion concentration) and the Revelle Factor would increase by 15%.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS41B2017J
- Keywords:
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- 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4813 Ecological prediction;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4815 Ecosystems;
- structure;
- dynamics;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL