Comment pubs.acs.org/est
Ocean Acidification: The Other Problem with CO2 n our most recent virtual issue, you will find several research articles related to the theme, “Ocean Acidification: Causes, Consequences, and Cures”. It is part of an effort to organize ES&T content for readers and draw added attention to important findings. These papers will commence a virtual series known as an “ES&T Select”. Climate change has been called the most vexing environmental problem of the 21st century, and ocean acidification (OA) is just one manifestation of it. It is caused by the increasing partial pressure of carbon dioxide, a weak acid, in sea surface waters (see 2014 National Climate Assessment). A wicked problem with an immense mass signature of CO2, ocean acidification foretells a long recovery period even after greenhouse gases are reduced in the atmosphere. But excess carbon dioxide is really TWO PROBLEMS. First, carbon dioxide is a “radiatively important” trace gas in the atmosphere, meaning it absorbs longwave back-radiation from the earth and warms the atmosphere. Part of that heat is transferred to the oceans and, indeed, a “top down” warming of the oceans is now occurring. Measured precisely by more than 3600 Argo solar-powered diving floats, ocean temperatures are increasing via a diffusive energy flux downward to a depth of over 700 m. This top-down warming cannot be explained by natural cycles of ocean circulationit can only be explained by heat-trapping gases warming the atmosphere and transferring that heat to the sea. To be sure, a huge amount of energy is already being transferred each year (roughly 20 times the amount of primary energy consumed in the world). Warming of the atmosphere and oceans is the first problem of CO2. The “other problem” of carbon dioxide−ocean acidificationmay prove to be even more intractable than a warming planet. Since the beginning of the industrial revolution, earth’s oceans have absorbed 560 billion tons of CO2 which has increased acidity by 30% and suppressed the pH of surface waters from 8.2 to 8.07. Ocean acidification cannot be fixed by “geoengineering” measures, like shooting reflective aerosols high into the stratosphere to cool the earth when things get really hot. Geoengineering cannot neutralize the acidity and the second problem will remain. There is no “silver bullet” other than halting fossil fuel emissions. We are locked-in to this “other problem” for many decades. I wish I could ask climate skeptics a simple question, “What level of CO2 are you willing to accept450, 550, 650, or 750 ppm? When should we start to stop?” Models project an ocean pH of 7.8 by the end of this century. Coral reefs and all organisms which calcify a shell are at grave risk. Climate skeptics remind us that Earth was much warmer in the geologic past and the acidity of the ocean has also fluctuated. Will not marine ecosystems adapt to these newly acidic conditions? I do not knowI suppose adaptation is possible. But events of millions of years ago are not equivalent to what’s happening today. Unfortunately, we are acidifying the oceans 50 times faster than the rate from interglacial periods during the past million years. If we bet on the ability of mussels and mollusks to evolve new bioenergetics for precipitating
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shells of aragonite or calcite at pH 7.8, we may lose. We are gambling with the entire oceanic food chain which helps sustain us. In this ES&T select, you will find new research on ocean acidification. Ecotoxicology is the subject of several of the articles. Thiyagarajan et al. (es-2014-01611u) discussed the deleterious effects of pH, elevated temperatures, and reduced salinities on the Pacific Oyster in Yellow Sea coastal waters; while Lewis et al. (es-2014-02739m) documented increased copper toxicity on the polychaete Arenicola marina at pH and pCO2 concentrations relevant to those expected in the 21st century. Higher pCO2 and ocean acidities are expected to cause dissolution of carbonate minerals and the release of toxic metals from sediments. Trafford et al. (es-2014-01564q), Riba et al. (es-2014-015373), and Levin et al. (es-201-00514j) published results on the dissolution of high magnesium-calcite minerals in Australian seabeds, toxic effects of sediments on amphipods in the Gulf of Caidiz, and geochemical proxies (U/Ca ratios in shells) for estimating integrated exposures of larval mussels, respectively. Widdicombe et al. (es-2014-01601w) used 1H NMR spectroscopy and metabolomics to report fascinating differences among male and female blue mussels, Mytilus edulis, in 90-day exposures to reduced seawater pH and increased temperatures. Understanding variability in carbon dynamics in the ocean is another piece of critical information; Zhang et al. (es-201400510z) show how this can be done with the example of Florida Bay. In order to measure these dynamics ES&T authors have also developed some valuable new instrumentation which should aid future OA studies including a deep-sea Free Ocean CO2 Enrichment system (dp-FOCE) and an autonomous instrument for high temporal resolution measurements of seawater alkalinity. Barry et al. (es-2014-01603r) showed early results from dp-FOCE on sea urchins. The device will allow sensitive measurements to be made in situ on deep-sea taxa with presumed low tolerance for ocean acidification. Spaulding et al. (es-2014-01615x) evaluated the performance of a Submersible Autonomous Moored Instrument for alkalinity (SAMI-alk) using a novel tracer monitored titration method. Pfister et al. (es-2014-01936p) provide a bookend to this Select with a Critical Review that suggests a research framework for ocean acidification, examines the current state of research in the United States and identifies funding needs. At ES&T, we hope these articles contribute to our role in analyzing the “other problem” of carbon dioxide. We trust you will find them interesting and important.
Jerald L. Schnoor,* Editor-in-Chief Published: September 16, 2014 10529
dx.doi.org/10.1021/es503107u | Environ. Sci. Technol. 2014, 48, 10529−10530
Environmental Science & Technology
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[email protected]. Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS. The authors declare no competing financial interest.
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dx.doi.org/10.1021/es503107u | Environ. Sci. Technol. 2014, 48, 10529−10530
