Acidifying Oceans Remake Earth And Our Food Supply

March 2008

What is going on in the world’s oceans? To the known problems of overfishing, pollution, and invasive organisms borne on ship hulls, we can add the lesser-known alterations caused by climate change.

What scientists had to say at the annual meeting of the American Association for the Advancement of Science in Boston last month was shocking: Atmospheric climate change is altering the chemistry of the ocean and, in the process, the marine life and seafood we depend on. These changes are very likely unstoppable.

Marine organisms may not have the genetic diversity to tolerate the changes that humans are causing in sea water.
— James Barry, Monterey Bay Aquarium Research Institute

Acidity is spreading

“Over 40 percent of the world’s ocean areas are heavily affected by humans, and very few if any areas remain untouched,” Benjamin S. Halpern, of the National Center for Ecological Analysis and Synthesis in Santa Barbara, Calif., declared at the meeting.

Halpern presented spectacular maps showing 17 ways that humans inflict harm on the oceans, which appeared in the 15 February Science. The huge atlas is built up of cells of data one-kilometer square for oceans, which cover 71 percent of the planet. Halpern told reporters he was surprised by the global spread of acidification.

Halpern Global Map of Human Impact Science Feb 15, 2008

The overwhelming cause of rising acidity is carbon dioxide—streams of the stuff that human activity spews into the atmosphere. Ocean acidification is “the other carbon dioxide problem.” This was the title of the main panel at which experts laid out these troubling issues.

Until recently, we thought the oceans helped get us off the hook for spewing so much carbon dioxide into the atmosphere. As Peter Brewer, an ocean chemist at the Monterey Bay Aquarium Research Institute, said: “The planet’s seas quickly absorb 25 to 30 percent of humankind’s carbon dioxide emissions and about 85 percent in the long run, as water and air mix at the ocean’s surface.”

True, but not the whole story. The curling action of waves scoops carbon dioxide into the surface water. When CO2 reacts with water, it forms carbonic acid (H2CO3). The carbonic acid breaks down into protons and bicarbonate, releasing hydrogen ions that react with the carbonate ions in the water. More CO2 means fewer carbonate ions. Carbonate ions are essential building blocks for the shells and skeletons of many marine organisms—for example, corals.

 So, as human activity packs more CO2 into the oceans, marine organisms that evolved in low-CO2 waters are less able to form properly.

Though there are fascinating exceptions the overall picture is grim. Corals in carbon-dioxide-rich seas already have thinner skeletons. Many such organisms will become extinct or their populations will be reduced, altering the marine food web, the panelists said.

Billions, no, trillions of teensy animals and plants are morphing to try to adapt. It is hard to grasp the reorganization of life on such a scale. And experts at the meeting stressed how little they know about the transformation. 

Acidity is speeding up 

We measure acidity and its opposite alkalinity in relation to water, which is neither. Water is neutral and assigned 7 on a logarithmic scale of 0 to 14. The most acidic substances are 0; as they get less acid, their values climb towards neutrality at 7. Above 7 substances become more alkaline, up to 14. 

The gastric juice in our stomachs is 2, or very acid. Lemon juice is 2.1. Fresh milk is 6.7. What is alkaline? Blood, for example, at 7.4.

Before the Industrial Revolution the world’s oceans (measured down to 200 meters) were mildly alkaline, averaging 8.2. But now that humankind has packed so much more CO2 into the seas by way of the sky, the ocean averages 8.1—still alkaline, but more acidic.

A change of 0.1 in the logarithmic scale in ocean water that is 71 per cent of Earth’s surface, in just 200 years, is a very big deal. Transformation will continue. “In 100 to 200 years, the planet will have an ocean it has not seen for the past 40 million years,” said James Barry, senior scientist at MBARI, at the AAAS meeting. Barry showed graphs comparing two well-known trends, using data from the Intergovernmental Panel on Climate Change.

One graph from the IPCC (top, blue line) shows atmospheric concentrations of CO2 from 400,000 years ago. As is well known, atmospheric concentrations passed historic peaks of about 370 ppmv in 2000. Concentrations could rise past 700 ppm if humanity continues “business as usual” with today’s power plants, vehicles, and industry. (Al Gore showed this chart in the film “An Inconvenient Truth.”)

Denser atmospheric CO2 will make the seas more acidic, as shown in Barry’s graph. Using IPCC data (lower, red line), Barry estimated the parallel changes in the acidity of the ocean surface over the same period.

The chart shows average acidity rising sharply in modern times—that is, pH dipping down. The average of the top 100 meters reached 8.1 by 2000. By 2100, it will be 7.8 or 175 percent more acidic than in 2000, Barry explained. 

Though the changes will be staggering, to a large extent they are unforeseeable even to scientists. Barry said, “Marine organisms may not have the genetic diversity to tolerate the changes that humans are causing in sea water over time.”

Double whammy: low oxygen

Marine organisms are being hit with a second huge stress: less oxygen (O2), the AAAS speakers explained. In today’s oceans, plants such as phytoplankton that grow near the surface add oxygen to the water. As surface water sinks, deeper water is oxygenated; life at the depths depends on this oxygen. Oxygen is also released as dying phytoplankton drift to the bottom. Today’s marine life forms have evolved based on to oxygen at various depths and times.

Yet the ocean surface is getting warmer as the air warms above it. The warmer ocean surface water is lighter, so it doesn’t sink as fast or as deep as before. So less oxygen reaches deep-sea marine organisms, even as—in a double whammy—the depths become more acidic.

 “The combination of low O2 and high CO2 is particularly deadly,” said Brewer. Indeed, a huge dead zone of zero oxygen was recently reported off the Oregon coast.

 “The largest daily migration on earth,” Brewer said, is made by vast populations of tiny calciferous organisms that move up to shallow waters by day and sink to depth by night, according to long-standing, subtle balances of O2, CO2 temperature, and light.

The mass movements of these organisms is are the basis of our global marine food web.

Poster children for our brave new world

The famous oceanographer Sylvia Earle is trying to raise alarums about the changing oceans. She often says that people care only about what they know. The problem with Earth’s morphing ocean is most of us don’t go diving, as she does. We don’t set sail as Messrs Barry and Brewer do armed with remote-control cameras and special lights to view the depths. The cause of slowing ocean acidification needs poster children: organisms whose present beauty and gnarled fates tug human hearts. Some candidates presented at the AAAS meeting: [Slides from Google Images.]  

The dot-sized coccolithophoreslook like hub caps stuck on a beach ball. They lack the polar bear’s primal grace. Their colors aren’t dramatic like the vibrant corals. But drifts of trillions of their milky shells are breathtaking seen from space. 

Coccoliths should be celebrities, Ulf Riebesell of the Leibniz Institute of Marine Science said at the meeting. His lab grows them in more acidic water and seen their plates deform. Riebesell described the changed life in a natural marine ecosystem that has evolved under high-CO2 and high-acidity conditions which has been studied by Jason Hall-Spencer of the University of Plymouth.

Closer to a sea-floor volcanic vent off the Italian coast, the water becomes more acidic by 1.5 on the scale. And there are fewer sea urchins, coralline algae, and stony coral. Why? In the more acidic water, these organisms cannot calcify. They’re the losers.

Who wins? There are more More invasive sea grasses and brown algae. Riebesell called for a massive assault on the problem of rising acidity because so little research is known.

The sea cucumber (Scotoplanes) (not pictured) looks like Eeyore in Winnie the Pooh, except for its four donkey-like ears; two of them trail from its hindquarters. 

The deep sea octopus (Starothuethus) is white with curious pink limbs – or fins. It peers at us curiously with a single eye halfway down its body.

The pteropod mollusk may be the loveliest ocean acidity poster child. These diaphanous marine snails are the principal food for juvenile salmon. If the pteropods go, what will salmon feed on? Salmon in warmer waters need more marine food, but there will be less food for them as waters warm.   

 “Oh brave new world, that has such creatures in’t,” Brewer of MBARI said quoting Shakespeare’s Tempest as he flipped through the images. Most of Earth’s six billion people will never see these organisms, even as rising CO2 emissions destroy their aqueous homes. 

The presenters at AAAS avoided crisis talk even as they forecast lower catches, more variation in stocks, and more ecosystem collapses.

What’s ahead?

 What species will survive in seas that are already more acidic than in the past 40 million years? Paleo-oceanographers look for answers in ancient remains of marine life on the sea floor. 

Presenters noted that many marine organisms survived when the oceans were very acid in the Cambrian and Ordovician periods from 600 to 400 million years ago. Also, small marine organisms beget several thousand generations in a century. One hypothesis is that maybe they can evolve at warp speed and outrun their changing habitat. 

But in ancient history, marine species had far longer to adapt to rising acidity than today’s creatures: the peaks and valleys of CO2 and O2 were gentler than now and the future.

Andrew H. Knoll of Harvard described the marine extinctions of about 252 million years ago, when 90 percent of creatures disappeared at end of the Permian period. Knoll said he doesn’t expect new extinctions on this scale. But the puzzle remains of how winners and losers [delete quotation marks on 2nd use] were sorted out. In the great Permian wipe-out, some species “didn’t seem to notice,” he said.

Barry of MBARI showed global maps of where acidity is likely to rise fastest under current CO2 emission scenarios. Meeting presenters and others seek a huge expansion of ocean research because we know so little of what’s happening now, let alone of the future.  

Their main plea is: Stop emissions now! Typical is the crisp conclusion of a lucid Royal Society Report on ocean acidification: “Action needs to be taken now to reduce global emissions of CO2 to the atmosphere to avoid irreversible damage to the oceans. We recommend that all possible approaches be considered to prevent CO2 from reaching the atmosphere.”

For a start we could wipe out the term “climate change” from our discourse. It misleads people to think the problem is limited to in the air and on the land.

“This thing is bigger than the words ‘warming,’ ‘global warming,’ ‘climate change.’ Many of these [impacts] are not about atmosphere,” said Carl Safina, president of the Blue Ocean Institute at the close of one session.

“We’re remodeling the planet,” he said.

The meeting was held in vast buildings that send emissions to the sky and sited near the Atlantic Ocean. At it, some 10,000 conference-goers tucked into meals of lobster, crab, and salmon. The catch has been plentiful this year, and prices are down.

But today’s ocean feasts may become history in the lifetimes of our children. 

© Deborah Shapley