World Oceans Day is today and we celebrate that which sustains us.

Welcome to World Oceans Day 2011. Since 2008, the United Nations has recognized June 8th as a day to celebrate, learn about, and take action on behalf of the oceans that cover three quarters of our planet and sustain all life on Earth – what author Julia Whitty calls our Deep Blue Home.

Last year at this time, oil was still spewing into the Gulf of Mexico from the mangled riser pipe of BP’s Deepwater Horizon oil rig. All told, more than 4 million barrels of oil were spilled, and nearly 800,000 gallons of the chemical dispersant Correxit were injected deep into the Gulf. On the one-year anniversary of the explosion that killed eleven men and started what President Obama called “the greatest environmental disaster of its kind,” oil spill researcher Chris Reddy told me it was still too soon to know how much oil and dispersant remains in the Gulf and what the long-term ecological impacts will be.

This year, as we recognize World Oceans Day, we wait for news of another environmental disaster – the ongoing nuclear crisis in Japan. Yesterday, Japan’s nuclear agency doubled their estimate of how much radioactive material has been released from the Fukushima Daichi nuclear power plant that was crippled by the March 11th earthquake and tsunami. In the weeks immediately following the disaster, levels of radioactivity in surrounding ocean waters skyrocketed. Now Bloomberg has reported that radioactive water may once again begin flowing into the ocean as it overflows service trenches. The announcement adds to the urgency of a research expedition now underway to map the location, type, and levels of radioactive contamination in the Pacific Ocean.

And yet, despite their devastating effects, these dramatic environmental disasters are not the greatest threats to our ocean.

Studies released in the past year have trumpeted dire news: nearly 60% of the world’s coral reefs are at risk of being lost in the next three decades, 85% of natural oyster reefs have already been lost, and it’s estimated that large fish have declined by two-thirds in the past century. These declines are largely the result of five human-driven processes that slowly but surely chip away at ocean ecosystems.

1. Climate Change: The ocean has absorbed more than 90% of the excess heat trapped by rising levels of greenhouse gases in the atmosphere. Rising water temperatures are driving commercially important fish species offshore and toward the poles in search of cooler climes – bad news for fishermen and seafood lovers alike. Warmer water also holds less oxygen, and that spells trouble for marine animals who – like us – breathe oxygen. Scientists recently warned that low-oxygen ‘dead zones’ are expanding, and that we could be in for a repeat of the mass extinctions triggered by prehistoric warming events.

 

Carbon dioxide emissions pose a double threat to the ocean, raising water temperatures and increasing acidity.

2. Ocean Acidification: Carbon dioxide doesn’t just build up in the atmosphere; about a third of it gets absorbed by the ocean. The inevitable chemical result is the production of carbonic acid that, in sufficient quantities, disrupts the acid-base balance of the ocean (thus, the term ‘acidification’). That, in turn, throws off a whole host of other chemical processes. Corals and shellfish can’t get the calcium carbonate they need for their skeletons and shells. And the microscopic marine plants upon which the entire ocean food chain depends may not be able to get the nutrients they need to grow. Scientists have generally considered ocean acidification to be a problem of the future, but a study published last fall forced a revision of that thinking by demonstrating that scallops and quahogs are already feeling the burn.

3. Pollution: Plastic, nutrients, pesticides, hormones, oil. The list of things we dump into the oceans is disconcertingly long. Last summer, a team of researchers from Woods Hole, MA, confirmed what many had long suspected – that plastic debris is accumulating in the middle of the Atlantic Ocean, just as we’ve known for decades that it does in the Pacific. Another recent study confirmed that the vast majority of plastic releases estrogenic chemicals when soaked in saltwater and exposed to sunlight.

But not all pollutants are chemicals. Some experts include ‘biological pollution’, or invasive species – plants and animals that are introduced by human activities, like global shipping, into areas they have never been before. These species often out-compete or outright kill native species. This year, we learned that rising water temperatures may be making a bad situation worse, giving invasive species a competitive edge over their native counterparts.

4. Overfishing: Ecosystems are like jigsaw puzzles: remove one piece and you can’t complete the puzzle. Remove several, and the puzzle may not hold together or form a recognizable image. In this way, overfishing and its cousin, by-catch, wreak havoc on ocean ecosystems. Of course, collapsed fisheries take a human toll as well, causing economic hardship and threatening food supplies.

Counting fish is no easy matter, and there is always controversy about the status of fish populations. This year was no different. A high-profile presentation at a high-profile scientific conference set off a renewed debate, with one side claiming that large, predatory fish could be virtually extinct by 2050 and the other arguing that the reductions in large fish are exactly what would be expected of well-managed fisheries. But scientists on both sides of the overfishing debate have agreed that more than half of fish populations worldwide need rebuilding.

Still, there’s some good news on the overfishing front today. Federal officials are optimistic that the 2010 fishing season may go down in history as the year U.S. fisheries set – and stayed within – science-based, sustainable fishing limits. The U.S. is just one country, but this is evidence that we have the tools necessary to end overfishing. The challenge is putting them to work in the places – like Asia – that need them most.

5. Ignorance: Less than 10% of the ocean has been explored by humans. We have better maps of Mars than the seafloor, and some oceanographers have compared their research to shining a flashlight into an immense, dark cavern. Last fall, scientists announced the completion of the Census of Marine Life – a decade-long, global effort to shine a light on the amazing diversity of life that inhabits the ocean. The efforts of more than 2,000 scientists raised the total number of known marine species to almost a quarter of a million. Still, they estimate that’s less than a quarter of what’s out there; the vast majority of ocean life remains unknown to science. That means that, even for the ocean scientists who know the most, the ocean is largely a big blue bag of mysteries. Susan Avery – Director of Woods Hole Oceanographic Institution – says that the greatest threat facing the ocean is our limited ability to see what’s beneath the surface, to truly grasp our impact on the vast expanses of ocean.

Lest you think this doom and gloom doesn’t affect you, let me remind you of a few key facts.

It is no exaggeration to say that the ocean sustains all life on Earth. To quote W.H. Auden: “Thousands have lived without love, not one without water.” The oceans contain 97% of all water on the planet and drives the global water cycle. We’d also be hard-pressed to live without air, and microscopic marine plants produce more than half the oxygen we breathe.

Almost half of the world’s species live in the ocean. That rich biodiversity is not only an ecological wonder, it’s a treasure trove of chemicals that show up in everything from ice cream to toothpaste, and could hold a cure for cancer.

And in the age of globalization, when what you’re wearing, eating, or driving is more likely to be made in China than made in the U.S.A., it’s worth remembering that more than 90% of international trading is conducted via the ocean.

Just as we all benefit from the ocean, we all contribute to the threats facing the ocean, and we can all do something to help.

The greatest threats facing the ocean start in our homes and workplaces, whether we’re five minutes or 500 miles from the beach. While beach clean-ups are a tried and true way to repair some of the damage we inflict, they’re far from the only way.

• Learn more about what the ocean does for us, and what we’re doing to it.

• Tell others what you’re learning.
• Eat fish responsibly: Buy local, if possible, and know how the fish you eat was caught. Look for the Marine Stewardship Council label or check with a consumer guide, like Seafood Watch or the Smart Seafood Guide. None of the guides or labels are perfect, but they’re better than nothing.
• Ditch disposable plastic: We may only use it once, but it stays in the ocean forever. Plastic shopping bags and water bottles are particularly egregious offenders. Invest in a reusable water bottle and some canvas shopping bags.
• Reduce your carbon footprint: Don’t know where to start? Try an online carbon footprint calculator or a home energy audit to pinpoint areas where you can reduce.

This story was originally published in Climatide.

Image: Nasa Goddard Photo, Mike Baird, rkraemer, laszlo photo

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