As we approach the phony hysteria over the end of the world this coming Friday, it’s worthwhile to consider some real threats to the planet. Climate deniers try to distort or obfuscate the evidence about the changing atmosphere, and it’s not always easy to give overwhelmingly conclusive data that would convince them. In some cases the data are tricky to analyze, or do not have well-documented long-term histories necessary to answer every concern about whether recent weather events are truly unprecedented. The atmospheric system is very complicated, with many different processes operating on short-term, medium-term, and long-term time scales, and not all of it is as well understood as we would like. Thus, the arguments over changes in earth’s atmosphere often reach an impasse.
Not so for the oceans. Although oceans are an even larger system than the atmosphere, we understand them much better. More importantly, we have an excellent long-term record of how the oceans have changed over millions of years from thousands of deep-sea cores, and from the paleontological record of marine fossils that goes back over 700 million years. And unlike the atmospheres, oceans change very slowly over time, since the thermal inertia of water makes the seas very resistant to change except on long-term time scales. In addition, most ocean currents move slowly compared to atmospheric currents. So no matter what you want to make of the data showing atmospheric change, the changes in the oceans are more alarming, since oceans require immense stimuli to cause such change.
A few years ago, marine biologist and film-maker Randy Olson (famous for his film “Flock of Dodos“, which lampoons not only creationists but also arrogant scientists who refuse to communicate with the public) founded a web-based effort to publicize the destruction of the oceans. Named “Shifting Baselines,” it refers to the fact that many ecological systems have shifted to a “new norm” or “new baseline,” and conditions no longer return to those they exhibited only 30 years ago. For example, long-term divers and marine biologists have all documented dramatic changes in the oceans, especially coral reefs. When Olson and most senior marine biologists began diving, coral reefs were thriving around the world, and these same people are now documenting the rapid deterioration of reefs around the world in a single lifetime. Thus, the “baseline” of what is considered normal marine diversity has changed in just a few decades, and biologists being trained today have a very different concept of “normal” marine diversity than those just 30 years ago. As my friend and colleague Jeremy Jackson of the Smithsonian put it, “Every ecosystem I studied is unrecognizably different from when I started. I have a son who is 30, and I used to take him snorkeling on the reefs in Jamaica to show him all the beautiful corals there. I have a daughter who is 17—I can’t show her anything but heaps of seaweed.” Or as marine biologist Steve Miller of the University of North Carolina, Wilmington, wrote:
“Caribbean coral reefs of the 1970s changed my life. But the reefs I first knew and loved are gone, casualties of disease, coral bleaching, and overfishing. The reefs I study now in Florida are only a shadow of their former glory. My tourist friends go snorkeling and marvel at the colors and structure, but little do they know they’re looking at the ghost of a coral reef. While I can tell my friends about all that we have lost, I am saddened that my children can’t have the same personal experience I had, just 25 years ago.”
Although overfishing and disease are certainly important problems in the oceans, the biggest problem seems to be that the oceans are becoming warmer and more acidic as they absorb the excess heat and carbon dioxide from the atmosphere and turn it into carbonic acid. For a long time, some people argued that we didn’t need to worry about carbon dioxide, because the oceans would serve as a big buffer and absorb it all. Well, if that were ever true, it is no longer. The evidence is overwhelming that the acidity of the ocean is changing faster than it has in 300 million years. This, more than any other factor, is responsible for the world-wide dying of the tropical coral reefs. Known as “bleaching,” it occurs when the individual coral polyps (which look like tiny sea anemones) cannot tolerate the environmental conditions, such as excess heat or acid ocean waters, any longer. They shed their symbiotic algae (zooxanthellae), which in normal times help them metabolize carbon dioxide and build their skeletons, and thus lose their color. Eventually, the coral polyps die off, leaving their huge stony skeletons behind which gradually turn white. Although some reefs, like the Great Barrier Reef of Australia, are also suffering from problems like out-of-control predation by the crown-of-thorns sea star, the worldwide bleaching and dying of coral reefs can only be attributed to a global oceanographic change—and only ocean warming and acidification fits that description. Certainly, there are certain marine organismsthat thrive in warmer, more acidic oceans (such as the algae that cause the deadly red tide, or encrusting algae growing on rocks uncropped, plus sand fleas, some less calcified crustaceans, and sea urchins), but the vast majority of marine species are negatively affected. Once the reef corals themselves die, nearly all the hugely diverse community of animals and plants vanishes soon thereafter, leaving a mass of dead stony coral rock covered by algae where once a gloriously beautiful and diverse reef community lived.
If the loss of the coral reefs and their huge effect on diversity were not worrisome enough, there is even more direct evidence of what ocean acidification is doing to the marine realm. Several studies have just reported new data that shows the shells of sea creatures are now dissolving faster than they can be grown. First spotted in the thin-shelled planktonic mollusks known as pteropods (or “sea butterflies”) in the Antarctic waters (where colder water allows higher carbon dioxide concentrations), this is an alarming sign. Once the rest of the world’s oceans become acidic enough, most calcareous shelled invertebrates (especially the world’s population of clams and snails, plus echinoderms, some sponges, and corals) will literally dissolve away as larvae before their shells can grow. In addition, the loss of the planktonic pteropods (and most other calcareous plankton, such as foraminifera and coccolithophorid algae) will wipe out the marine plankton that are the base of the food chain throughout the world’s oceans. Once the plankton vanish, so do their predators higher up, leading eventually to most of the world’s fish and whales, all of which feed on smaller animals from lower in the food chain. This would cause a dramatic extinction in the world’s oceans. It would have adverse effects not only on our need for seafood to help provide protein for some of the 7 billion people on the planet, but dead oceans have a huge effect on the atmosphere as well. Once the calcareous planktonic algae vanish, they remove our largest absorber of carbon dioxide from the atmosphere, since the world’s planktonic algae have a much bigger effect on atmospheric carbon dioxide than do the land plants in rainforests and elsewhere (which are also diminishing due to deforestation).
Even more alarming is how quickly this is all happening. In one lifetime, marine biologists have witnessed widespread mass extinction in the coral reef community, and the first signs of oceans so acidic that the marine shelled organisms are dissolving before our eyes. As studies have shown, this is faster than at any time in geologic history, even the famous “methane burp” event 55 million years ago which caused a sudden spike in carbon dioxide and worldwide mass extinction in the ocean.
As I mentioned above, we have 700 million years of ocean history recorded in the fossil record, especially in the deep-sea cores that record the past 100 million years in great detail. We can analyze the carbon isotopic composition of shells of planktonic microfossils and show how the ocean chemistry has changed. We can look at the patterns of diversity and extinction of acid-sensitive marine fossils, and find out when the ocean has experienced this kind of “acid bath” before. As a recent article by Hönisch et al. (2012) pointed out, the current episode of mass extinction and rapid acidification of the ocean has no precedent. The closest we can come to is the worst mass extinction in earth history, the “Great Dying” at the end of the Permian Period, about 250 million years ago. The extinction was so severe that about 95% of marine species vanished, and a similar number of land species as well. Although the complete causes are complex and still under discussion, there is a clear signal from the chemical isotopes that there was a global warming event, as well as too much carbon dioxide in the seawater (hypercapnia). It is thought to have been driven by the largest volcanic eruption in earth history, which occurred in northern Siberia. As these eruptions released greenhouse gases, they drove the delicate chemical balance in the oceans to supersaturation in carbon dioxide and highly acidic conditions. Between the toxicity of hypercapnia and the effects of dissolving shells, nearly every group of animals in the oceans vanished 250 million years ago. These included many groups, such as rugose and tabulate corals, trilobites, and blastoid echinoderms, that had survived many previous oceanic mass extinctions. Other groups, such as the brachiopods, the bryozoans, the crinoids, the bivalves and gastropods, and the ammonoid cephalopods nearly vanished, with only a few subgroups surviving to repopulate the world later.
The fossil record provides us with a sobering lesson: what we’re doing to our atmosphere is bad enough, but what we do to the oceans is even deadlier, even if it is less visible to us landlubbers. Previously, all the focus has been on the mass extinction in land animals caused by humans and their associated animals, but the devastation of the oceans is far worse. The last time it was this bad, life nearly vanished from this planet.
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