Climatological distributions of pH, pCO2, total CO2, alkalinity, and CaCO3 saturation in the global surface ocean, and temporal changes at selected locations

Abstract

Climatological mean monthly distributions of pH in the total H + scale, total CO 2 concentration (TCO 2 ), and the degree of CaCO 3 saturation for the global surface ocean waters (excluding coastal areas) are calculated using a data set for pCO 2 , alkalinity and nutrient concentrations in surface waters (depths <50 m), which is built upon the GLODAP, CARINA and LDEO databases. The mutual consistency among these measured parameters is demonstrated using the inorganic carbon chemistry model with the dissociation constants for carbonic acid by Lueker et al. (2000) and for boric acid by Dickson (1990). Linear potential alkalinity-salinity relationships are established for 24 regions of the global ocean. The mean monthly distributions of pH and carbon chemistry parameters for the reference year 2005 are computed using the climatological mean monthly pCO 2 data adjusted to a reference year 2005 and the alkalinity estimated from the potential alkalinity-salinity relationships. The equatorial zone (4°N-4°S) of the Pacific is excluded from the analysis because of the large interannual changes associated with ENSO events. The pH thus calculated ranges from 7.9 to 8.2. Lower values are located in the upwelling regions in the tropical Pacific and in the Arabian and Bering Seas; higher values are found in the subpolar and polar waters during the spring-summer months of intense photosynthetic production. The vast areas of subtropical oceans have seasonally varying pH values ranging from 8.05 during warmer months to 8.15 during colder months. The warm tropical and subtropical waters are supersaturated by a factor of as much as 4.2 with respect to aragonite and 6.3 for calcite, whereas the cold subpolar and polar waters are supersaturated by 1.2 for aragonite and 2.0 for calcite because of the lower pH values resulting from greater TCO 2 concentrations. In the western Arctic Ocean, aragonite undersaturation is observed. The time-series data from the Bermuda (BATS), Hawaii (HOT) and the Drake Passage show that pH has been declining at a mean rate of about -0.02 pH per decade, and that pCO 2 has been increasing at about 19 atm per decade tracking the atmospheric pCO 2 increase rate. This suggests that the ocean acidification is caused primarily by the uptake of atmospheric CO 2 . The relative A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 importance of the four environmental drivers (temperature, salinity, alkalinity and total CO 2 concentration) controlling the seasonal variability of carbonate chemistry at these sites is quantitatively assessed. The ocean carbon chemistry is governed sensitively by the TA/TCO 2 ratio, and the rate of change in TA is equally important for the future ocean environment as is the TCO 2 in ocean waters increases in the future.

Two decades of inorganic carbon dynamics along the West Antarctic Peninsula

“…Neglecting these important drivers may be responsible for the large RMSE of our predicted TA (Fig. A2) relative to other studies that either had additional parameters at hand (i.e., O 2 or nutrients) to derive inorganic carbon system parameters in coastal environments (Juranek et al, 2009;Kim et al, 2010;Evans et al, 2013) or used salinity algorithms to predict TA in open-ocean regions (Takahashi et al, 2014). Furthermore, TA varied by more than 70 µmol kg −1 at salinities > 33.7, which led to an unbalanced distribution of residuals (Fig.…”

“…We observed the strongest but still statistically insignificant increase in surface pCO 2 in fall (1.9 µatm yr −1 , p = 0.0685). This increase corresponds with the mean atmospheric pCO 2 increase of 1.9 µatm per year, which causes a pHT decrease of about 0.02 per decade (Takahashi et al, 2014). Interestingly, Stammerjohn et al (2008a, b) found that sea-ice extent and wind are also changing most rapidly in spring and fall, which may enhance sea-air gas exchange and therefore facilitate positive pCO 2 trends.…”

Spatiotemporal Assessment of CO2–Carbonic Acid System Dynamics in a Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern Hawaiian Islands

“…Sabine and Mackenzie (1995) examined the water column surrounding select atolls within the monument. Their results demonstrated an alkalinity surplus of roughly 10 lmol kg -1 from 0 to 1000 m depth, relative to alkalinity values expected for subtropical waters within the central North Pacific Subtropical Gyre (NPSG) (Millero et al 1998;Dore et al 2009;Takahashi et al 2014). The observed alkalinity surplus (i.e., ''the alkalinity halo'') was interpreted to be a consequence of the dissolution of soluble mainly biogenic magnesian calcite particles transitioning offshore from the atoll reefs and lagoons along the island slope.…”

Spatiotemporal variability of alkalinity in the Mediterranean Sea

“…Global climatology has been produced for pH and alkalinity (Lee et al, 2006;Takahashi et al, 2014), often based on the use of empirical site-specific regressions between alkalinity and temperature and salinity data. In the open sea environment, alkalinity often correlates with salinity and temperature (Lee et al, 2006;Takahashi et al, 2014).…”