A Gas-Controlled Aquarium System for Ocean Acidification Studies

Ocean carbon sequestration by direct carbon dioxide injection to the deep-sea or by the fertilization of the upper ocean with iron to accelerate the biological pump are methods under consideration to mitigate rapidly rising atmospheric carbon dioxide levels and avoid, in part, excessive greenhouse gas warming. Both sequestration efforts will elevate carbon dioxide levels in the deep ocean, which after reaction with the seawater carbonate system, will decrease the pH of the ocean. In addition, ocean acidification is occurring through the passive influx of carbon dioxide through the ocean surface. Efforts to understand the effects of accelerating ocean acidification from carbon sequestration efforts or passive CO
₂
absorbance will require study of marine ecosystems from the surface to the deep-sea. In many deep-sea environments, hypoxia can also be stressful for marine organisms. Therefore, studies to assess the impacts of ocean acidification in deep-sea habitats should also include examination of the effects of hypoxia, due to the potentially synergistic interaction between these stressors. In this report, we describe the development of a gas-controlled aquarium (GCA) system used for laboratory studies of the effects of hypoxia or ocean acidification or both on marine animals. The GCA system is capable of regulating the temperature, oxygen, and carbon dioxide content of waters in three aquarium tanks for use in assays of growth and metabolic rate studies or various marine animals. The GCA design uses a main reservoir and 3 aquarium tanks in which different set-points for oxygen and carbon dioxide levels are possible. Membrane contactors connected to recirculation pumps and gas sources are used to control gas concentrations in each tank. A LabVIEW software system integrated with mass flow controllers for oxygen, carbon dioxide, and nitrogen sources allows real-time, automated regulation of gas concentrations in each tank.