Oceans cover nearly three-quarters of the surface of the Earth, reach depths of nearly seven miles, and contain 321 million cubic miles of water. In Byron's day the sea floor was a mystery, most marine life forms were unimagined, and mankind bobbed uneasily on the surface in an effort to travel, trade, explore, and conquer, never certain of remaining topside. The ocean takes on the persona of a deity in this work, "boundless, endless and sublime – the image of eternity – the throne of the invisible." Only in the absence of a human imprint can a place take on such a role, as is well understood by cultures that prohibit the climbing of certain mountains or other rock structures, such as Denali in Alaska or Spider Rock in Arizona, so their spiritual qualities will not be lost.

Two centuries later the situation has changed utterly. Once considered the Earth's last frontier, the ocean has become familiar and somewhat better understood, and man's steps are all over its paths. If familiarity has not bred contempt, it has bred recklessness of multifarious, at times even criminal, sorts.

Among the greatest of these is overharvesting of marine animals, which had its origins in Byron's century when many of the great whale species were hunted nearly to extinction in the quest for lamp oil. By the mid-twentieth century the rapidly increasing harvesting of fish led to the development of industrial fishing, whose methods are often indiscriminate, wasteful, and short-sighted. They have all but wiped out numerous species, beginning with the Atlantic cod and herring and the California sardine, creating a massive disruption to the food chain that grew from a regional and worrisome situation to a global and catastrophic one. The loss of biodiversity in the ocean has been linked to the more rapid decline of the species that remain, and a diminished ability of ecosystems to recover.1 Sixty-three percent of fish stocks are currently in trouble,2 with the predicted total collapse of all the world's fisheries by 2048 if present trends continue.3 Even the sea floor itself, with its rich and highly-developed habitat, is entirely destroyed by fishing methods such as bottom trawling and the use of dynamite.

Like the atmosphere, the ocean is also warming. Its great inertia makes this process a slow one, but even minute temperature differences can lead to enormous consequences. Krill, for instance, a shrimplike crustacean that is a vitally important food for many marine species, reproduce in far smaller numbers when temperatures begin to rise. Coral is the organism most vulnerable to warming; a slight temperature increase can cause it to bleach (eject its symbiotic algae), making it susceptible to disease and large-scale die-off. Coral reefs, known as the rainforests of the sea, are the greatest providers of habitat for marine biodiversity. Yet thanks to tankers and anchors, careless boaters and snorkelers, blast fishing, sunlight-blocking silt, and especially rising temperatures and ocean acidification, they are vanishing at an alarming rate, and may succumb entirely by the end of this century.4 (For more on coral see Rachel Carson under Browse by Author.)

For tens of millions of years the oceans enjoyed a relatively stable level of acidity, which helped to form the environment in which its rich web of life evolved. But more recently, with the addition of large quantities of CO2 to the atmosphere, this has been dramatically altered. Roughly half of CO2 emissions are absorbed by the oceans, some 22 million tons a day. While this slows the warming of the atmosphere, it has increased the acidity of the oceans by some 30% over the two centuries since Byron remarked on their imperviousness to man's ravaging.5 Not only does this contribute to the dissolution of coral, it also jeopardizes the ability of shellfish, algae, and zooplankton to maintain their protective shells, and threatens the survival of many fish and shellfish species in their larval stages.

Pollution and garbage are among the more visible insults to the ocean. Pesticides and herbicides, detergents, petrochemicals, and sewage run into the sea from rivers, streams, and outfall pipes. Nitrogen-rich fertilizers wash off farmland and make their way to the coasts and out to sea, where they cause massive algae blooms that deplete the oxygen from the water, leaving dead zones where nothing can live. There are currently some 400 dead zones around the globe, including one the size of New Jersey that forms every summer around the Mississippi River Delta.

Then there is the Great Pacific Garbage Patch, a rotating mass of mostly plastic debris, located between Hawaii and California and estimated at twice the size of Texas. Of the more than 60 billion tons of plastic produced each year, much ends up in the ocean,6 where it releases toxins into the water, entangles and chokes seabirds, marine mammals, and sea turtles, and blocks the digestion of animals who mistake it for food. The U.N. Environment Programme estimates that there are 46,000 pieces of floating plastic for every square mile of ocean.7 And the quantity is increasing rapidly; additional garbage patches have been reported, and some concentrations are growing by tenfold every decade.8

There is also aural garbage, in the form of high-intensity sonar. The U.S. Navy uses it to detect enemy submarines; but the testing of it often takes place in whale migration corridors and feeding grounds. Whales are heavily reliant on underwater sound to locate mates and food, and to follow migration routes and communicate with each other. The intensity of the sound not only disrupts these essential activities, but causes tissue damage and massive internal bleeding in many cases, resulting in the beaching and death of large numbers of whales.

And there is oil. Oil reaches the ocean's waters from several sources, some on land (spills from trucks and trains, terrestrial pipelines and storage tanks), some at sea (tankers and barges, underwater pipelines, offshore drilling). Between 1970 and 2000 there were over 250,000 spills in U.S. waters alone.9 While tankers are involved in only a small portion of spills, their spills tend to be among the largest. There have been far more tanker spills in the Gulf of Mexico than in any other location around the world. But until now, only some two percent of the volume of oil spilled in U.S. waters came from offshore facilities such as oil rigs.10

Apart from the sickening sight of oil sheens on the surface of the water and tar balls washing up on beaches, oil in the ocean in large quantities is a death sentence for massive numbers of fish, birds, marine mammals, sea turtles, corals, zooplankton, and others. It prevents fur and feathers from insulating animals and leads to death from hypothermia. It enters the digestive systems of birds when they preen, and poisons them. It causes skin lesions and burns, neurological impairment, damage to internal organs, lowered hemoglobin levels, and a host of other lethal effects. It destroys wetlands and barrier islands, the rich habitat they supply, and the protection they provide against storm surges. Dispersants used to break up the oil may do even greater harm in deep water, where they deplete the oxygen in the water and create enormous dead zones.

The current state of our oceans reflects the two centuries of extreme carelessness that have produced it. Yet just as there are many sources of trouble, there are also many sources of hope. Scientists studying biodiversity loss in the oceans believe that most fisheries can still recover, with appropriate management. Retailers and restaurants are beginning to promote sustainably caught seafood, and taking threatened species off their shelves and menus. Regulations are beginning to appear that aim to rein in some of the plastic detritus that is so prevalent, especially plastic shopping bags. Efforts are being made to avoid whales' migratory routes and feeding grounds when testing sonar. Warming, acidification, and the dissolution of coral, on the other hand, are massive problems that await a workable solution to climate change.

As for oil, tanker safety has been greatly enhanced by the phaseout of the single-hull tanker.11 Offshore drilling presents challenges that can't be so easily remedied. Arctic drilling seems especially fraught with risk, and proposals to do just that are awaiting approval. Aldous Huxley famously remarked that one of the most important lessons of history is that man doesn't learn very much from history. In the case of the Deepwater Horizon spill, if the enormity of the lesson plays any role in bringing it home, we can hope that something may yet be learned.

1 Worm, B; Barbier, EB; Beaumont, N; Duffy, JE; Folke, C; Halpern, BS; Jackson, JBC; Lotze, HK; Micheli, F; Palumbi, SR; Sala, E; Selkoe, KA; Stachowicz, JJ; Watson, R. "Impacts of biodiversity loss on ocean ecosystem services." Science 314: 787-790. Nov 2006.

2 Worm, B; Hilborn, R; Baum, JK; Branch, TA; Collie, JS; Costello, C; Fogarty, MJ; Fulton, EA; Hutchings, JA; Jennings, S; Jensen, OP; Lotze, HK; Mace, PM; McClanahan, TR; Minto, C; Palumbi, SR; Parma, AM; Ricard, D; Rosenberg, AA; Watson, R; Zeller, D. "Rebuilding global fisheries." Science 325: 578-585. Jul 2009.

3 Worm, B et al., Op. Cit. (2006).

4 National Oceanic and Atmospheric Administration. "State of the Science Fact Sheet: Ocean Acidification." May 2008.

5 Ibid.

6 Walsh, Bryan. "Expedition sets sail to the great plastic vortex." Time, Health and Science: Aug 1 2009. Online. http://www.time.com/time/health/article/0,8599,1914145,00.html.

7 UNEP. "Marine litter: an analytical overview." 2005. http://www.unep.org/regionalseas/Publications/Marine_Litter.pdf.

8 Weiss, Kenneth R. "Plague of plastic chokes the seas." Los Angeles Times: Aug 2 2006. Online. http://www.latimes.com/news/printedition/la-me-ocean2aug02,0,5594900.story.

9 Thompson, Andrea. "The Science and History of Oil Spills." Live Science: Environment. 23 Apr 2010. Online. http://www.livescience.com/environment/oil-spill-faq-100423.html.

10 Ibid.

11 International Maritime Organization. "Tanker safety – preventing accidental pollution." 2002. http://www.imo.org/Safety/mainframe.asp?topic_id=155.