Can Acid Neutralizers Help Coral Reefs Bounce Back?

Apr 18, 2013
Originally published on April 18, 2013 8:35 pm
Copyright 2017 NPR. To see more, visit


OK. Yesterday on this program, we took you to Heron Island on Australia's Great Barrier Reef. Scientists there are accumulating evidence that coral reefs are in trouble because of climate change. Two problems here, actually: one is the warming waters, the other is the increasing acidity of the water caused by rising levels of carbon dioxide. Today, we're going to take you to another island on the Great Barrier Reef and meet scientists who were testing whether an acid neutralizer can help - think Tums, for coral. NPR's Richard Harris continues his report.

RICHARD HARRIS, BYLINE: If you pump carbon dioxide into an aquarium that contains coral, the coral will eventually die. Carbon dioxide makes the water more acidic, and eventually that can melt away a coral's mineral skeleton. Ken Caldeira wants to find out what happens to coral on an actual reef. On this blustery day, he's sitting in a small boat in a lagoon ringed by a coral reef at One Tree Island.

KEN CALDEIRA: And this is a very unusual lagoon, because the wall around this lagoon forms, like, a bathtub, and the water's kind of flowing over the rim of the bathtub.

HARRIS: And we're parked right now, right, on the lip of the bathtub.

CALDEIRA: Right. And so what we are going to do is measure the water as it flows over this lip of the bathtub.

HARRIS: This natural setting provides Caldeira an unusual opportunity to measure the chemistry of the water before and after it washes across the reef. If the reef is growing, it will suck calcium carbonate out of that water in order to build its stony skeleton.

CALDEIRA: From that difference in the chemistry of the water as it flows over the lip, we can tell how fast this coral reef is growing.

HARRIS: But Caldeira isn't simply measuring the normal growth. He's trying to find out if the reef will grow faster if he puts antacid in the water. In theory, it should, because the reefs could absorb the minerals it needs much better if the water is less acidic. And the ocean is more acidic now than it used to be. That acid started out as carbon, in the form of fossil fuels. When we burn those fuels, carbon dioxide flowed into the atmosphere, and lots of that carbon dioxide soaked into the ocean, becoming carbonic acid.

CALDEIRA: So our goal is to try to show that ocean acidification is already negatively impacting coral reef growth. But as you know, well, we might be trying to show that, as good scientists, we'll let the data lead us wherever it leads us.

HARRIS: And it's not a simple matter to answer that question. The first challenge is to bring a half a dozen people and a whole bunch of sampling gear out onto the reef.

CALDEIRA: Watch out. That's heavy.

HARRIS: Once the gear is out of the aluminum skiff, we head across the reef - this natural bathtub rim - toward the heart of the experiment.

CALDEIRA: So, just be careful there. Try to step on sand, and not on coral.

HARRIS: This is kind of precarious for me. I'm carrying my recording gear while I'm walking through about a food of seawater and trying to keep my balance. We make our way to a spot near where a second skiff is anchored. Ken's wife, Lilian Caldeira, has taken a break from her job as a software executive to help out on the reef. We see her in the distance wrestling with clear plastic pipes.

CALDEIRA: Lilian is putting in place what we call the quadrupus, which is basically some one-inch diameter tubing that branches out into four arms.

HARRIS: One tube snakes back to a flexible floating tank designed by a chemist named Jana Maclaren. She has mixed antacid with some red dye in the tank, and is prepared to pump it out into the reef. Caldeira calls out to her.

CALDEIRA: How many minutes until we start pumping? Two minutes till we start...

JANA MACLAREN: (unintelligible)


HARRIS: Caldeira looks around to make sure everything is set to go. There's a squall heading our way, but they'll work through it. Chemical monitoring canisters are in place, so are bottles ready to capture samples of water. The moment has finally arrived.

MACLAREN: Five, four, three, two, one - pump it.

HARRIS: So, red fluid is now coming through these clear pipes and trickling out onto the reef. It's like a very light, red wine. Caldeira is from the Carnegie Institution of Science. He's assured the Australian authorities that the dye is harmless and that the antacid will, if anything, make the reef grow faster. As the red fluid spans across about 100 feet of the reef, Lilian Caldeira makes last-minute plans to sample the chemistry.

LILIAN CALDEIRA: So, I think syringes will be, I think, (unintelligible).

HARRIS: At carefully timed intervals, team members slurp up samples of water in giant syringes. They also fill smaller sampling bottles. Most of this will get analyzed at a sophisticated chemistry lab back on One Tree Island.


HARRIS: This is the second year Caldeira has attempted to measure the growth of this reef. The first try was a flop. With the experimental setup working pretty well at this moment, he at least has a fighting chance of coming up with a result, though he is looking for a very small change.

CALDEIRA: This stretch of reef in front of us will probably put on something like a pound of calcium carbonate in this hour. You know...

HARRIS: Just under normal circumstances.

CALDEIRA: Yeah. And we're looking to that to maybe increase by two ounces, or something like that. So it's a challenging thing to do.

HARRIS: Challenging, and the stakes are high. The basic chemistry of carbon dioxide suggests that coral reefs are in mortal danger. They can cope with the current changes in ocean chemistry, but we are likely approaching a tipping point. The ocean will become so acidic, reefs may lose their mineral skeleton faster than they can rebuild it.

CALDEIRA: Based on other work we've done, we've projected this, and more or less every reef in the world will be dissolving somewhere in the middle of this century.

HARRIS: Is there anything that can be done about that?

CALDEIRA: I think the only real thing we can do is transform our energy system.

HARRIS: Caldeira says we need to stop putting all that carbon dioxide into the air, to preserve the reefs. Antacid treatments aren't even a Band Aid. His experiment is more about studying a problem, not finding a cure.

CALDEIRA: It might be possible to do something like what we're doing on a larger scale to protect the reef in some particular bay or enclosed area. But the scale of effort that would even be needed to protect this one lagoon would be so enormous.


HARRIS: The fundamental problem is that we're adding carbon dioxide to the ocean so fast, the ocean's natural ability to neutralize acid is simply overwhelmed. Normally, the acid balance in the ocean is neutralized by minerals on the seabed that gradually dissolves.

CALDEIRA: If we were putting out the same amount of carbon dioxide, but we put it out over 100,000 years instead of 100 years, there would be no problem.

HARRIS: But the last time the ocean chemistry changed so abruptly was a disaster for the corals. That's when the dinosaurs went extinct 66 million years ago. Eventually, the ocean chemistry and the reefs recovered, but just getting the chemistry back took tens of thousands of years.

CALDEIRA: If the future is anything like the past, it might be many hundreds of thousands of years before the reefs reestablish themselves.

HARRIS: And in the meantime, the world's oceans would be a much cooler place. Out here on this pristine outpost of reef, you get the sense that Ken Caldeira is trying to soak up the essence of a place that may not survive another human generation. Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.