In 1996, Columbia University researchers used Biosphere 2’s marine mesocosm to recreate three sets of ocean conditions: those of a glacial ice age, the present day, and the 22nd century. The researchers alternated between these conditions at three-month intervals over three years, according to the University of Arizona’s Biosphere 2 ecosystems page . Every three months, an ocean in the Arizona desert took a trip through time. The experiment examined how changing carbon dioxide levels and seawater chemistry affected photosynthesis and coral calcification.
Originally designed to simulate a Caribbean coral reef, the enclosed ocean system has a surface area of 35 by 20 meters and holds 2.6 million liters of water. A 1999 paper in Ecological Engineering , The Biosphere 2 coral reef biome , describes an initial mixture of roughly 10% natural seawater from the Southern California coast and 90% local well water combined with commercial sea salt. The glacial scenario used a CO2 partial pressure of 200 microatmospheres and a pH of 8.29. Present-day conditions used 360 microatmospheres and a pH of 8.08, while the 22nd-century scenario used 900 microatmospheres and a pH of 7.89. In a 2000 study published in Global Biogeochemical Cycles , Chris Langdon and colleagues reported that their long-term measurements predicted a 40% decline in net coral reef calcification between 1880 and 2065 as seawater carbonate saturation decreased. By February 2026, that effort had reached a major milestone: researchers had introduced 108 coral fragments into the Ocean Habitat for the first time in more than 30 years. Researchers can now use the 2.6-million-liter habitat to investigate coral growth, environmental stress, and possible approaches to reef restoration under controlled conditions.
Updated lighting, circulation, and temperature-control systems support the work. The tank behind the experiment is no ordinary aquarium. Mechanical systems reproduce or replace natural processes, allowing researchers to adjust temperature , water mixing, gas exchange, nutrient concentrations, and carbon dioxide pressure independently. its water supply did not need to come from the Caribbean Although the facility models a tropical reef. The three experimental scenarios differed in carbon dioxide concentrations and seawater chemistry. The declining pH values indicated increasingly acidic seawater. This finding describes the projected change in net reef calcification over that period, rather than a uniform decline across all three experimental scenarios. The ocean habitat later deteriorated after a period of neglect. The University of Arizona’s research account explains that algae and cyanobacteria overgrew the substrate, and nearly all the original animals disappeared, leaving about two dozen hardy fish. The team attached the corals to specially designed structures as part of research into how they respond to higher temperatures.
Since then, researchers have worked to rehabilitate the ecosystem.
