[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,

When growing on urea as a nitrogen source, diatoms must accumulate nickel (Ni), a cofactor in the urease enzyme, which hydrolyzes urea. The uptake of Ni at low ambient concentrations is particularly challenging in view of the slow rate of reaction of the Ni 2+ ion with uptake ligands. As expected, cultures of the model diatoms Thalassiosira weissflogii and Thalassiosira pseudonana become limited at very low Ni concentrations when growing on urea but not on nitrate or ammonium as a nitrogen source. At high Ni concentrations, ureagrown cultures of T. weissflogii exhibit similar accumulation of various other metals to nitrate-grown cultures and the same sensitivity to zinc and copper (Zn and Cu) concentrations.