26 Oceanus Magazine Vol. 46, no. 1, 2008 www.whoi.edu/oceanusit’s sort of the planetary equivalent of mov-ing clutter accumulating in the attic to other storage space in the basement: trans-ferring excess heat-trapping carbon diox-ide from earth’s atmosphere into the deep ocean. a combination of forces—including rising public awareness and concern about climate change, international treaties, and growing carbon trading markets—has com-bined to spark so-called geoengineering pro-posals to do that. Ocean iron fertilization is just one of several of these ideas. Here are a few others that apply to the oceans:Injecting CO2 into the Depths scientists from MiT, columbia, and Harvard universities have suggested that carbon dioxide from industrial plants could be captured and piped into seafloor sed-iments—a variation of older proposals to dump cO2 into ocean depths greater than 3,000 meters (almost 2 miles). Freezing temperatures and intense pressure would turn the carbon dioxide gas into a dense liq-uid heavier than the water above, so that it would stay in deep-sea storage and out of the atmosphere. The idea would also capitalize on un-used real estate. undersea sediments along the u.s. coastline, for example, may be suf-ficient to store the nation’s annual carbon dioxide emissions for thousands of years, researchers said in the august 2006 issue of the Proceedings of the National Academy of Sciences.Opponents of the idea argue that adding billions of tons of carbon dioxide into the ocean in large, concentrated doses would alter the oceans’ water chemistry, have det-rimental impacts on sensitive marine organ-isms, and send harmful ripples through the food chain. also, possible leakage back to the surface remains a question.industrial plants would need to be ret-rofitted with devices to harness emissions (something that would be required also for other proposals to store cO2 underground). additional costs would come from inject-ing the cO2 via pipes, likely from a ship or a platform (similar to those used with ocean drilling) through nearly two miles of salt water into the seafloor. Fertilizing the Ocean with NitrogenThe Ocean nourishment corp. (Onc) in australia has proposed injecting large amounts of urea—a nitrogen compound found in mammalian urine and fertilizers—into low-nitrogen seas to stimulate phyto-plankton blooms and draw down excess cO2 from the air. Like land plants, phytoplankton require (along with sunlight, water, and cO2) not just iron but nutrients such as nitrogen to grow, but most tropical and subtropical ocean regions have too little of this essential nutri-ent, resulting in low productivity. in Onc’s plan, coastal factories using tanker-supplied natural gas would produce urea, pump it through pipelines, and release it at the edge of the continental shelf to stim-ulate phytoplankton blooms. in theory, phy-toplankton growth would both pull cO2 out of the atmosphere and also provide abundant food for zooplankton and fish, increasing fish stocks for people. carbon “locked” in dead plankton and fish tissue may eventually sink and be sequestered in the ocean depths.To be effective, the proposal would have to be worldwide. it would require at least 1,000 times more nitrogen than iron to fer-tilize equivalent blooms. several unresolved issues make the idea complicated: increased coastal nitrogen could promote blooms of toxic algae (“red tides”); the altered ocean chemistry could lead to unanticipated and permanent ecosystem changes; it remains unproved that more carbon-containing de-bris will sink to the deep ocean; and the factories and ecosystem changes would be disproportionately in poor tropical countries.Onc is a commercial venture eager to sell rights to use its licensed method in trop-ical regions to obtain carbon-offset credits. The company reportedly has conducted at least one small-scale experimental release of one ton of urea in the sulu sea, bound-ed by the Philippines and Borneo, and has further plans to test a release of 1,000 tons. The first release was near a highly biodi-verse area and a World Ocean Heritage site, prompting protests, partly because Onc may not have secured adequate Philippine government permission. A Rash of Proposals Emerges to Transfer Excess Carbon into the OceanJack Cook, WHOITUBING THE OCEAN—Increasing urgency about climate change has spurred proposals, which may have seemed radical not too long ago, to reduce atmospheric carbon dioxide levels. In a recent issue of the journal Nature, scientists James Lovelock and Chris Rapley pro-posed putting thousands of giant plastic tubes in the ocean (see next page). Wave motion and a one-way valve would push deep water through the tubes to the surface, bringing up essential nutrients to stimulate blooms of tiny marine plants. These phytoplankton would help draw down heat-trapping carbon dioxide from the air and also emit a chemical called di-methyl sulfide, which stimulates the formation of clouds that would block solar radiation and help cool the planet, the scientists say.About 100 to 200 metersOne-wayva lv eCO2H2OH2OWOOds HOLe OceanOgraPHic insTiTuTiOn 27Speeding Up Chemical Weathering researchers from Harvard and Penn-sylvania state universities have outlined a process that mimics the natural weathering of rocks, but accelerates the process—trans-ferring carbon from air to sea over decades, rather than millennia.carbon dioxide (cO2) in the atmosphere naturally dissolves in fresh water (H2O) such as rain, forming weak carbonic acid (H2cO3). as rainwater percolates down through volcanic rocks, chemical reactions produce bicarbonate (HcO3-) salts that flow into the ocean. Bicarbonate dissolves readily in seawater, allowing the ocean to retain and store more atmospheric cO2. in an article published nov. 7, 2007, in the journal Environmental Science and Tech-nology, the researchers propose building dozens of solar-powered plants in remote volcanic islands, such as in the south Pa-cific or the alaskan archipelago. The plants would split seawater to get hydrogen ions that would be combined electrochemically with the chlorine in salt to produce hydro-chloric acid, which is stronger than carbonic acid. The hydrochloric acid would then be sprayed on nearby rocks to react with al-kaline materials before flowing back into the ocean—as occurs in nature, only much faster. (as a side benefit, the researchers say, the process could also combat the growing acidification