Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO(2), global warming, and ocean acidification over the past ~300 million years of Earth's history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry-a consequence of the unprecedented rapidity of CO(2) release currently taking place.

s m i t h s o n i a n c o n t r i b u t i o n s t o t h e m a r i n e s c i e n c e s • n u m b e r 4 0 SerieS PublicationS of the SmithSonian inStitutionEmphasis upon publication as a means of "diffusing knowledge" was expressed by the first Secretary of the Smithsonian. In his formal plan for the Institution, Joseph Henry outlined a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This theme of basic research has been adhered to through the years by thousands of titles issued in series publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: In these series, the Institution publishes small papers and full-scale monographs that report on the research and collections of its various museums and bureaus. The Smithsonian Contributions Series are distributed via mailing lists to libraries, universities, and similar institutions throughout the world.Manuscripts submitted for series publication are received by the Smithsonian Institution Scholarly Press from authors with direct affiliation with the various Smithsonian museums or bureaus and are subject to peer review and review for compliance with manuscript preparation guidelines. General requirements for manuscript preparation are on the inside back cover of printed volumes. For detailed submissions requirements and to review the "Manuscript Preparation and Style Guide for Authors," visit the Submissions page at www.scholarlypress.si.edu. s m i t h s o n i a n c o n t r i b u t i o n s t o t h e m a r i n e s c i e n c e s • n u m b e r 4 0 Although commonly 2-10 cm in thickness, Clathromorphum can reach a thickness of up to 50 cm while forming an annually layered structure that can reach currently documented ages of up to 850 years. Geochemical and growth information archived in annual growth bands of Clathromorphum sp. has been used to provide long time series of past environmental conditions in regions that are poorly understood major drivers of Northern Hemisphere climate. However, information on Clathromorphum calcification, growth, and ecology that would allow interpretation of these records has previously been quite limited. Here we relate extensive field and laboratory data on the biology, physiology, and ecology of species of this genus and their controlling environmental parameters. We show that Clathromorphum has evolved a unique mode of double calcification, with high-magnesium calcite crystals, that enhances long life and leads to a multielement climate archive. Growth rates are controlled by temperature, and carbonate density is controlled by light, determined by both latitude and sea ice cover, whereas carbonate buildup and ultimate thickness are determined by local geomorphology and faunal interactions. Reproduction is complexly linked to vegetative anatomy. Precise paleoenvironmental...

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