<P> A report from NOAA scientists published in the journal Science in May 2008 found that large amounts of relatively acidified water are upwelling to within four miles of the Pacific continental shelf area of North America . This area is a critical zone where most local marine life lives or is born . While the paper dealt only with areas from Vancouver to northern California, other continental shelf areas may be experiencing similar effects . </P> <P> A related issue is the methane clathrate reservoirs found under sediments on the ocean floors . These trap large amounts of the greenhouse gas methane, which ocean warming has the potential to release . In 2004 the global inventory of ocean methane clathrates was estimated to occupy between one and five million cubic kilometres . If all these clathrates were to be spread uniformly across the ocean floor, this would translate to a thickness between three and fourteen metres . This estimate corresponds to 500--2500 gigatonnes carbon (Gt C), and can be compared with the 5000 Gt C estimated for all other fossil fuel reserves . </P> <P> Eutrophication is an increase in chemical nutrients, typically compounds containing nitrogen or phosphorus, in an ecosystem . It can result in an increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations . </P> <P> The biggest culprit are rivers that empty into the ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans . An excess of oxygen - depleting chemicals in the water can lead to hypoxia and the creation of a dead zone . </P>

What are three elements absorbed by marine plants