COMMENTARY A changing ocean seen with clarity Peter G. Brewer1 Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 he Hawaiian archipelago, the modern accurate spectrophotometric erties of total CO2 and alkalinity. These most remote group of islands ratio techniques (4) and applied these can be fundamentally calibrated and are on Earth, has long been associ- with extraordinary care to obtain an al- required data for incorporating the CO2 ated with the world’s most rec- most 20-year record of pH changes at system in ocean circulation models. But Tognizable image of global change. The the now legendary station ALOHA off the methods recommended still relied Mauna Loa atmospheric CO2 record, Hawaii. The dedication is extraordinary, on glass electrodes and on a complex begun in March 1958 by Charles David and the results are unassailable. They array of thermodynamic constants. It Keeling, shows with startling clarity the show that the change in surface ocean was inevitable that trouble would follow saw-tooth pattern of the seasonal CO2 properties produces a ‘‘long-term (7) with a decade of inconsistent data changes of land vegetation, and the still decreasing trend in surface layer pH from the world-wide Geosecs expedition astonishing, dominating, rise forced by that is indistinguishable from the rate of that took heroic efforts to untangle (8). fossil fuel burning which is rapidly acidification expected from equilibration New nonelectrode techniques were de- changing our world. Within perhaps only with the atmosphere.’’ veloped, standards were created, and 5 years the peak in the annual signal Why should this finding be impor- internal consistency was found. atop Mauna Loa will touch the 400 ppm tant? The annual changes in pH in sur- Geochemists were then happier with by volume mark, which would have been face waters off Hawaii are in milli-pH the state of the art, and rapid progress inconceivable to scientists of the first was made. As a result, time series sta- half of the twentieth century. But there tions were established at Bermuda (9) is one huge and environmentally critical Ocean uptake of fossil and Hawaii (10) with the purpose of signal that is not easily seen in the detailed tracking of oceanic biogeo- ‘‘Keeling curve,’’ and that is the oceanic fuel CO2 is now chemical cycles through time. These sta- uptake of fossil fuel CO2. In this issue tions and the record that flows from of PNAS, Dore et al. (1) document with proceeding at about them are now part of the crown jewels great clarity the changes in ocean CO2 of US global change science. From these chemistry and pH occurring in the 1 million metric tons and other data ocean chemists could ocean in the waters off Hawaii from uncover the massive imprint of the fossil fossil fuel CO2 invasion. of CO2 per hour. fuel CO2 signal (11). Background But communicating the consequences of these changes to the broader commu- The changes in pCO (partial pressure units, but the downward trend is clear. 2 nity, and to physiologists concerned with of CO ) in the atmosphere are exactly Why have such changes not been rou- 2 the inner workings of marine animals, paralleled in the ocean, but the conse- tinely documented for approximately the proved hard. By reporting on mass quences are very different. CO has no same time as the atmospheric CO 2 2 properties, and assuming that the pH atmospheric chemistry and is simply record? Is a slavish response to the at- changes were understood, ocean scien- mixed. But increasing CO2 in sea water mosphere all that will occur? Will the induces changes in pH, and Dore et al. deep ocean waters respond to change in tists did not get their message out; the (1) have measured these changes with the same manner as the ocean surface? required language simply was not there. remarkable accuracy and precision. Are there impacts that will be felt by In a 2004 lecture to a fisheries meeting I They thereby forcefully link air and sea marine life, or perturbations of carefully remarked: ‘‘So complex is the full ac- and provide unmistakable evidence of poised biogeochemical cycles? counting of this process that the mes- ocean acidification and the complex and The seemingly simple matter of accu- sage has often been blurred. The use of a confusing set of apparent thermody- still poorly understood consequences of rate measurement of oceanic CO2 sys- this. And they go beyond the simple sur- tem properties, and in particular pH, namic constants, the existence of several face expression to explore the changes has engaged scientists for a long time. pH scales, the arcane distinctions be- taking place at depth. Early investigators routinely made very tween pCO2 and fCO2, the strictures on Large-scale uptake of atmospheric large numbers of electrode-based pH careful measurement, and the use of fossil fuel CO2 has long been recognized measurements around the world. But in these systems in dynamic models have (2) as a fundamental consequence of the words of Keeling (5) ‘‘These investi- all deterred the non-specialist.’’ the acid–base balance of slightly alka- gators, in their optimism for having line ocean surface waters, poised at found a simple measuring routine, failed Public Awareness about pH 8.2, exposed to an atmosphere to note that the new method was Breakthroughs in public awareness oc- of steadily increasing CO2 (3). The scarcely capable of detecting the small curred in a strange way. Direct disposal quantities involved are huge. Ocean up- changes in pH of surface ocean water of fossil fuel CO2 in the ocean as a take of fossil fuel CO2 is now proceed- that reflect significant changes in pCO2.’’ means of climate control had been ad- ing at about 1 million metric tons of These measurements were therefore of vocated as early as 1977 (12), but when CO2 per hour, and the accumulated bur- little practical use for tracking the even very-small-scale experiments took den of fossil fuel CO2 in ocean waters is changes taking place. now well over 530 billion tons. A major improvement was initiated in But the direct measurement of the pH 1967 with the call by the influential chem- Author contributions: P.G.B. wrote the paper. The author declares no conflict of interest. changes brought about by this CO2 up- ist Lars Gunnar Sillen (6) for pressure– take has challenged ocean scientists for temperature-independent data, and for See companion article on page 12235. decades. Dore et al. (1) have taken accurate measurement of the mass prop- 1E-mail: [email protected]. www.pnas.org͞cgi͞doi͞10.1073͞pnas.0906815106 PNAS ͉ July 28, 2009 ͉ vol. 106 ͉ no. 30 ͉ 12213–12214 Downloaded by guest on September 27, 2021 place (13) the images obtained aroused doubling of atmospheric CO2 (ϷpH Ϫ For surface waters this typically has a environmental concern as no graph or 0.3). There is strong evidence that this is value of Ϸ10. But colder, deep waters in table ever could. A typical reaction was not controlled by an external surface which pH and carbonate ion have al- ‘‘My God! You are going to change equilibrium process. Rather the coral- ready been much reduced by the addi- pH.’’ This new medium conveyed the line animal actually engulfs sea water tion of respiratory CO2 have far less message. With a formal assessment of into an internal vacuole and works to buffer capacity. Thus the changes in the engineering issues and biological form the skeletal material from the en- both pCO2 and pH created at depth as consequences by the Intergovernmental closed fluid. Although an increase in the CO2 invasion moves into abyssal wa- ters will far exceed the surface changes Panel on Climate Change (IPCC) (14) temperature could extend the latitudinal now widely discussed in the ocean acidi- the door was opened. A critical meeting range of some corals, the net result of fication literature. The relatively well- held in Paris in 2004 (15) shaped the the combined effects of warming and oxygenated deep waters off Hawaii mea- rapidly emerging field of ocean acidifi- acidification is likely to be strongly sured by Dore et al. (1) hint at this cation studies (16), and a cascade of negative. process. important papers followed. Hawaii is surrounded by vast expanses For an extreme case Brewer and Pelt- The first concern was for changes in of coral reefs, but interestingly Dore et zer (20) have recently investigated the calcification, with impacts on coral reefs al. (1) do not directly address this issue. changes at an eastern Pacific station and pelagic organisms with calcareous Instead they step tentatively onto new where O2 levels are very strongly de- shells (17). The 20-year record in sur- ground. They report on the vertical pro- pleted, and CO2 highly enriched, at only face waters off Hawaii shows only a files of changing pH in the ocean water 500-m depth. There surface waters la- Ϫ0.03 pH unit change. But extrapolating column and note that the rate of change beled by a doubling of atmospheric CO2 backwards to the preindustrial era indi- ‘‘is elevated within distinct subsurface and translated to depth will raise the cates that a modern change of Ϫ0.1 pH strata.’’ The deeper strata are colder pCO2 from about 1,000 ppm to 2,000 has already occurred. And projecting waters formed at higher latitudes, but ppm and more. The equivalent changes forward using well-known IPCC scenar- they take time to transit from their in pH will occur. These extraordinary ios shows that a change of about Ϫ0.3 point of equilibration with the atmo- numbers pose a challenge not simply for pH should occur by mid-century.