Our oceans, the cradle of life, account for about 70 per cent of the Earth's surface and are home to a diverse range of life, from marine mammals like whales and dolphins to fishes, corals, crustaceans and exotic micro-organisms. Many, like the food fishes, are crucial to us and the oceans, as natural carbon sinks, perform an important role in maintaining atmospheric gaseous equilibrium through the carbon cycle.
But rising levels of atmospheric carbon dioxide, due to the unbridled burning of fossil fuels especially over the last two to three decades, are causing the climate to warm resulting in rising water temperatures, and the oceans to become increasingly acidic.
A recent report, "Turning Up the Heat: How Global Warming Threatens Life in the Sea," by the World Wildlife Fund and Marine Conservation Biology Institute in June 2007, indicated that rising global temperatures are impacting ocean ecosystems to a far greater extent then previously thought. Wide spread changes are occurring across the entire marine food chain, from plankton, corals, fishes, seabirds to penguins and polar bears.
Coral reefs, the most biologically diverse and beautiful marine ecosystems, are suffering unprecedented devastation due to high surface water temperatures, with large numbers in the Pacific and Indian Oceans, the Persian Gulf and the Mediterranean Sea, losing their polyps, turning completely white and dying - a process called bleaching. As a result, thousands of species of fishes and invertebrates that depend on the habitats that the reefs provide are in danger.
Dying corals off Florida's coast 1975 - 1995Unchecked warming would also wipe out most of the habitat of the salmon species, eg. the Pacific Sockeye salmon, as they are extremely temperature-sensitive. In the waters off Australia, warmer oceans have sparked mass migration of species like the yellow-fin tuna, stinging jellyfish and sea turtles to the cooler waters in the south while in California, reef fish and inter-tidal invertebrates including sea anemones, crabs and snails are moving toward the poles in response to warming.
The biomass of phytoplankton, tiny marine plants that many marine organisms depend on for food, has also declined as a result of warmer oceans. Data released by researchers from the Oregon State University, after a ten-years analysis, indicated that phytoplankton productivity from 2000 onwards, declined by 190 million tons of carbon each year, with carbon as a unit of measurement of the amount of carbon dioxide they remove from the atmosphere through photosynthesis.
The study clearly showed that overall phytoplankton biomass decreases as the climate warms. This also creates a vicious cycle. As carbon dioxide levels rise, with decrease in phytoplankton production, there will be less ocean plants to absorb this green house gas.
Coral bleachingThe declined in plankton biomass has also contributed to decreased reproduction and increased mortality of seabirds due to starvation as these plankton form the base of the birds' food chain. Between late 1980s and early 1990s, California's Sooty shearwaters population declined by 90 percent and Cassin's auklets by more than 50 per cent. Common murres also died by tens of thousands.
Besides warmer ocean temperatures, the rising amount of atmospheric carbon dioxide is also causing our oceans to be increasingly acidic which will adversely affect many organisms that use calcium carbonate for their skeletons and shells, including corals and molluscs. Carbon dioxide, when dissolved in the oceans, becomes carbonic acid and excessive amount of carbonic acid lowers the pH of the oceans, increases its acidity and endangers marine life.
This drop in ocean pH is especially damaging to hard-shell marine animals such as corals and shellfish that use calcium carbonate, a critical mineral, for the formation of their shells and growth. However, a more acidic ocean will easily dissolve calcium carbonate, just like a piece of chalk dissolving in vinegar.
For decades, the oceans' absorption of carbon dioxide have been viewed as an environmental plus, as it mitigates the effects of global warming. But by taking up about 30 per cent of the atmosphere's carbon dioxide, mainly produced through the burning of fossil fuels, our oceans ph levels have dropped by about 0.1 units on the 14-point scale since the Industrial Revolution.
Scientists expect that carbon dioxide emissions, if left unchecked, will further reduce the oceans ph levels by another 0.3 units by 2100 and the increased ocean acidification will have serious repercussions to all marine life from the smallest marine micro-organisms, molluscs, corals to large marine mammals like whales.
Failure to check and reduce carbon dioxide emissions today may mean that there will be no place in the oceans of the future for many of the species and ecosystems that we know today.
-World Wildlife Fund
-Oregon State University
-National Oceanic and Atmospheric Administration
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