Revelle revisited: Buffer factors that quantify the response of ocean chemistry to changes in DIC and alkalinity

Abstract

[1] We derive explicit expressions of the Revelle factor and several other buffer factors of interest to climate change scientists and those studying ocean acidification. These buffer factors quantify the sensitivity of CO 2 and H + concentrations ([CO 2 ] and [H + ]) and CaCO 3 saturation (W) to changes in dissolved inorganic carbon concentration (DIC) and alkalinity (Alk). The explicit expressions of these buffer factors provide a convenient means to compare the degree of buffering of [CO 2 ], [H + ], and W in different regions of the oceans and at different times in the future and to gain insight into the buffering mechanisms. All six buffer factors have roughly similar values, and all reach an absolute minimum when DIC = Alk (pH $ 7.5). Surface maps of the buffer factors generally show stronger buffering capacity in the subtropical gyres relative to the polar regions. As the dissolution of anthropogenic CO 2 increases the DIC of surface seawater over the next century, all the buffer factors will decrease, resulting in a much greater sensitivity to local variations in DIC and Alk. For example, diurnal and seasonal variations in pH and W caused by photosynthesis and respiration will be greatly amplified. Buffer factors provide convenient means to quantify the effect that changes in DIC and Alk have on seawater chemistry. They should also help illuminate the role that various physical and biological processes have in determining the oceanic response to an increase in atmospheric CO 2 .Citation: Egleston, E. S., C. L. Sabine, and F. M. M. Morel (2010), Revelle revisited: Buffer factors that quantify the response of ocean chemistry to changes in DIC and alkalinity, Global Biogeochem. Cycles, 24, GB1002,

The impact of sedimentary alkalinity release on the water column CO<sub>2</sub> system in the North Sea

“…Of this, 1.0 mmol C m −2 d −1 is already supplied by internal DIC generation, and so, the remainder of 0.96 mmol m −2 d −1 will be supplied by CO 2 uptake from the atmosphere. The CO 2 uptake for the SNS as a whole amounts to 98 Gmol C yr −1 , which is around 14 % of the total CO 2 uptake of the entire North Sea (Thomas et al, 2004;Egleston et al, 2010). This value is slightly lower than the estimate by Thomas et al (2009), who calculated that sedimentary A T can potentially facilitate up to 25 % of the total CO 2 uptake of the North Sea.…”

“…The direction of a CO 2 flux between the surface water and the atmosphere is determined by the pCO 2 gradient between water and atmosphere, which is ultimately governed by the ratio of internal DIC over internal A T release (Frankignoulle, 1994;Egleston et al, 2010;Hu and Cai, 2011b). As shown above, the net generation of alkalinity amounts to 2.40 mmol m −2 d −1 .…”

Generalised expressions for the response of pH to changes in ocean chemistry

“…(4)) of Hofmann et 81 al. (2010a), and conceptually equivalent to the inverse of the buffer capacity (Morel and 82 Hering, 1993) and the buffer factor β A T of Egleston et al (2010). We first derive general 83 explicit equations for the sensitivity of protons and acid-base species to changes in ocean 84 chemistry.…”

The sensitivity of estuarine aragonite saturation state and pH to the carbonate chemistry of a freshet-dominated river

“…5c), DIC changes to the system independent of TA generally impact estuarine pH most severely where DIC ∼ TA (Egleston et al (2010), S ∼ 12-20 for the Fraser-Strait of Georgia), creating a salinity zone of 5 particularly strong sensitivity (Hu and Cai, 2013). These future DIC increases will shift this zone to higher salinities.…”

“…However, these high TA river estuaries also experience their zones of strongest seasonal pH sensitivity at higher salinities than their low TA counterparts, which likely impact a larger areal extent of the estuary (this zone is different than the zone of maximum pH sensitivity to changes in DIC alone which occurs at DIC∼TA (Egleston et al, 2010)). In this regard, seasonal pH changes in the Strait of Georgia driven by mixing alone are large (∆pH > 0.15) because the Fraser (red star, Fig.…”