Emerging Science of a High CO2/Low pH Ocean

Science Background

The invasion rate of atmospheric fossil fuel CO2 into the surface ocean now exceeds ~1 million tons CO2/hour, and the ocean has already absorbed some 500 billion tons of CO2 since the start of the industrial era. The resulting acidification of the ocean is now well established by observation, and a pH drop of 0.3 pH units from the pre-industrial level is now anticipated in the second half of this century. The biogeochemical consequences of this change are largely unknown and are now widely debated. Major reports have been issued by SCOR/IOC, the UK Royal Society, and a specially convened NSF-NOAA-USGS workshop. Over 20 years ago the terrestrial science community wrestled with a similar problem – the impact of elevated CO2 levels on land plants. When it was recognized that enclosed greenhouse studies had severe limitations, the Free Air CO2 Enrichment (FACE) techniques were created. This technology has now been adopted world-wide within the terrestrial ecology community. We propose to investigate the impact of CO2 enrichment on marine ecosystems by taking the similar, but far more difficult, step for ocean science with the intent of making the tools developed similarly available to the oceanographic community world-wide. Such controlled perturbation techniques would be suitable for investigating the impacts on a variety of oceanic communities including benthic, midwater and reef systems. This approach is consistent with MBARI’s fundamental mission of pairing scientists and engineers for the development of better procedures, systems, and methods.

The oceanic invasion of fossil fuel CO2, and the resulting reduction in ocean pH, has been recognized by the ocean geochemistry community for decades. The status of the oceanic CO2 system was a fundamental part of the GEOSECs program in the 1970s, the TTO program in the early 1980s, and the JGOFS program in the late 1980s-early 1990s. Recognition of the changing status of the carbonate dissolution depth was widespread (Andersen and Malahoff, 1977), and early work on the impacts of elevated CO2 levels on calcification in corals (Gattuso et al., 1998; Gattuso et al., 1999; Leclercq, 2000) was carried out in experimental mesocosms (Langdon et al., 2002). Thus this topic is of compelling and long standing intellectual interest to a very large segment of the ocean biogeochemical community.

But the larger scientific world paid scant attention to this issue until serious debate arose over the issue of the intentional sequestration of fossil fuel CO2 in the ocean by industrial means, and the first deep-sea disposal experiments were proposed and executed (Brewer et al., 1999; Tamburri et al, 2000). This helped crystallize many of the latent concerns over the possible impact of elevated CO2 levels on marine organisms and in November 2003 an international workshop on this topic was convened at the University of Kyoto and RITE (Kita and Ohsumi, 2004, and related papers). In May 2004 at a meeting held in Paris under the auspices of SCOR/IOC (Cicerone et al., 2004), the possibility of oceanic pH levels dropping by 0.3 pH units or more was reviewed based upon the likelihood of the various energy generation pathways identified by the IPCC actually occurring. Since then reports by the Royal Society (2005) and a NSF-NOAA-USGS workshop (2006) have all reached similar conclusions: that the reduction in oceanic pH is largely inevitable, that the changes anticipated are large and will very likely exceed those experienced on Earth over perhaps the last 25 million years, and that some marine ecosystems may have significant difficulty in coping with this change.

Over the last few years, a large number of innovative experiments have been carried out to examine these impacts. These have ranged from small scale pCO2 controlled aquarium studies (Kurihara and Shirayama, 2004) to large scale mesocosm experiments (Zondervan et al., 2001; Riebesell, 2004; Delille et al., 2005). But all of these studies have necessarily involved manipulation of enclosed systems. There is no doubt that these are representative of specific trends – but they cannot indicate all the features of an ecosystem response: predation on weakened animals, effects of reduced calcification on animal survival, recruitment of more CO2 tolerant species, effects on reproduction, migration, adaptation, etc. In order to fully to simulate this array of effects and observe directly the changes that would occur as CO2 levels rise and the complex ecosystems adjust we would have to consider the development of a form of Free Ocean CO2 Enrichment (FOCE) experiments. These experiments would necessarily draw upon the heritage of two decades of successful experimental work on land ecosystems. This is a daunting, but not impossible, task. There are many puzzles and unknowns. For example, although experimental work on corals shows significant reduced calcification in tank studies, the predicted thinning of coral growth bands from the already present pH reduction of 0.1 pH has not yet been detected. There are as yet no answers to questions of adaptation, of selection of CO2 tolerant species, etc. Yet society asks such questions, and expects informed answers from our community.

Questions? Comments? Please contact Edward Peltzer.


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Emerging science of a high CO2/low pH ocean