American Scientist

SEASICK: Ocean Change and the Extinction of Life on Earth. Alanna Mitchell. x + 161 pp. University of Chicago Press, 2009. $25.

At the conclusion of his Darwin Medal Lecture at the 11th International Coral Reef Symposium in 2008, Terry Hughes, who is director of the Australian Research Council’s Centre of Excellence for Coral Reef Studies at James Cook University, projected two side-by-side images onto massive screens in the darkened hall. On the left was an image of a canoe in which two passengers sat, comfortably dry and smiling. On the right was the same canoe, only upside down, with the passengers in the water. Hughes explained that these are the two equilibrium states for a canoe: upright and capsized. At equilibrium, the canoe resists shifting from one state to the other. But with enough forcing, a tipping point is reached at which the canoe can shift rapidly into the opposite state of equilibrium, sometimes to the dismay of the passengers.

Hughes’s apt metaphor underscored a key message of his lecture: that coral reefs have tipping points as well. And although they may resist change at first, showing few outward signs of stress, when shifts do take place, they can occur more rapidly than anyone had previously predicted and are tremendously difficult to reverse.

This warning forms the backbone of Seasick: Ocean Change and the Extinction of Life on Earth, by veteran science journalist Alanna Mitchell. Mitchell trawls the oxygen-depleted oceanic dead zones in the Gulf of Mexico, counts the days after the full moon in Panama to figure out when to search for signs of coral spawn, questions what a souring ocean chemistry holds for the future of marine plankton communities, and recounts the actions that have depleted global fisheries, documenting the toll that one frightening assault after another has taken on our ocean. Their cumulative effect has pushed us across a threshold. It appears that global systems may already be unable to return the ocean to its former state and are beginning instead to interact to create a new, far less hospitable state.

Faced with the myriad ways humans are changing the ocean, Mitchell admits that giving in to despair would be easy. Instead, she chooses a personal voyage of discovery in an effort to get to the bottom of things—in some instances literally (more on that later). Immersing herself in what Richard Feynman called “the pleasure of finding things out,” she goes straight to the primary sources, traveling with top scientists and taking part in their fieldwork. Nancy Rabalais, Ken Caldera, Joanie Kleypas, Nancy Knowlton, Boris Worm, Jerry Blackford—her list of mentors and guides reads like a fantasy lineup of ocean-science all-stars.

Mitchell’s quest for reasons to be hopeful is daunting. At one point, on a grueling 11-day oceanographic cruise near New Orleans, she works to sample and map a small portion of the dead zone, a 17,000-square-kilometer area of water south of Texas and Louisiana, where the Mississippi River discharges into the Gulf of Mexico. Heavy agrochemical runoff into the Mississippi eventually spills into the Gulf, where it acts as fertilizer for phytoplankton, creating massive algal blooms. The blooms eventually die and sink, and bacterial decomposition effectively depletes any available oxygen from the surrounding water. Over time, layer by layer, dead zones stack up atop the continental shelf. Mitchell notes that as a result of climate change, dead zones are both increasing in number (there are now more than 400 of them globally) and thickening, as the top of the stack moves closer to the surface.

Mitchell finds connections between ocean distress and climate change nearly everywhere she goes. Looking for spawning coral in Panama, she discovers that its reproductive cycle has been weakened as a consequence of coral bleaching caused by increased sea-surface temperatures. She climbs the Pyrenees in Spain with geologists who are searching for evidence of climate disruptions during the Paleocene-Eocene Thermal Maximum, a dramatic warming of the Earth’s atmosphere that took place 55 million years ago. But perhaps of greatest concern to her is the insidious threat to oceans posed by high levels of carbon dioxide in our atmosphere. When atmospheric carbon dioxide dissolves in seawater, it forms carbonic acid. The more CO₂ there is in the atmosphere, the more acidic seawater becomes; ultimately this reduces the amount of carbonate that is available in the water. Carbonate is critical for the formation and maintenance of calcium carbonate, which makes up the shells of mollusks and planktonic foraminiferans as well as the limestone that coral polyps produce to create reef architecture.

Here Mitchell’s scientist guides can offer little comfort. No one has come up with a way to mitigate the threat posed by ocean acidification. Mitchell writes hopefully of the possibility that the nations of the world will set targets that maintain atmospheric CO₂ levels near 380 parts per million. But news from the recent Copenhagen Climate Summit makes that seem unlikely.

Yet despite the book’s barrage of grim realities, and setting aside for the moment the fact that Mitchell overestimates the effectiveness of both the International Convention for the Regulation of Whaling and the Convention on International Trade in Endangered Species, I found the argument for hope and change that she presents compelling.

At the start of the final chapter, overwhelmed by the thought that the ocean may be terminally ill, Mitchell finds herself on the verge of despair. Nevertheless, she resolves to go through with a trip to a depth of 3,000 feet in a submersible. There she experiences a resurgence of hope:

Shivering in my undersea womb, peering at these wondrous, ancient life forms, it occurs to me that we are in an era that holds out the potential of magnificent regeneration. We could, if enough of us wanted to, form a new relationship with our planet. We could become the gentle symbionts we were meant to be instead of the planetary parasites we have unwittingly become.

As Mitchell emphasizes in the epilogue, the future is in our hands.

Rick MacPherson is a marine ecologist and is Conservation Programs Director for the Coral Reef Alliance, an international biodiversity conservation organization working exclusively to protect coral reefs. His interests include the history and philosophy of science and evolutionary theory.