How to Kill the Ocean—and Life as We Know It

The disputes about global warming and climate change seem to center on whether or not the effects are being caused by human activities. The answer to that should be obvious, but even the doubters should be concerned because whatever the reason, things could go very badly for humanity—and all other life forms.

Somewhat lost in the discussion is the status of our oceans. We are told that rising sea levels will inundate many of the coastal areas where much of our population resides. However, that could only be the beginning.

Sylvia A. Earle provides some perspective on our relationship with the oceans.

"There are many reasons for despair about the future of the ocean—and therefore, of humankind. The ocean is, in effect, our life-support system, driving climate and weather, governing the water cycle, stabilizing temperature, generating most of the oxygen in the atmosphere, taking up much of the carbon dioxide, shaping planetary chemistry. If the ocean is in trouble, so are we."

She also provides a status report.

"In the middle of the twentieth century, it seemed the ocean was too vast, too resilient, for humans to cause any harm. Now we know otherwise. Since the 1960s, 90 percent of many sought-after fish are gone, including sharks, tuna, swordfish, marlin, and many others. Half the coral reefs, mangrove forests, and seagrass meadows have been destroyed or are in a state of sharp decline. Hundreds of ‘dead zones’ have formed in coastal waters, while phytoplankton has declined globally by as much as 40 percent. Excess carbon dioxide released into the atmosphere is causing the ocean to become more acidic. The increase in jellyfish blooms is one of the many signs signaling a sea change."

These quotes were from Earle’s Introduction to Lisa-ann Gershwin’s book Stung!: On Jellyfish Blooms and the Future of the Ocean. We will use this source for information on relevant oceanic dynamics.

Gershwin’s view of the future is appropriately pessimistic.

"A great many books—some of which are fascinating reads—have been written on climate change, overfishing, and the pollution of our ecosystems. But there is a pattern to these books that I believe is not completely accurate, and is perhaps somewhat misleading. They leave the reader with the feeling that if we would just stop polluting, everything would be okay—that if we would just stop overfishing, the oceans would return to normal. These ideas sound good, but are not what we observe actually taking place."

The damage we do can have primary effects that we notice, but there are many secondary effects that are less obvious.

"When we think of overfishing, we forget that the warming waters of climate change are reducing the dissolved oxygen, making it harder for fish to respire and survive, and thus further contributing to the loss of fish. When we think of pollution, we think of smelly nasty corners of marinas, or beer cans and plastic drink bottles washed up on beaches, but we don’t think about the heavy metals or pesticide residues accumulating in our food supply and in our own bodies as a result….or about the excess nutrients flowing into estuaries and bays, creating vast dead zones…."

Gershwin now believes that we have passed a point of no return and the changes we have caused are irreversible.

"I now sincerely believe that it is only a matter of time before the oceans as we know them and need them to be become very different places indeed. No coral reefs teeming with life. No more mighty whales or wobbling penguins. No lobsters or oysters. Sushi without fish."

"In their place we shall see blue-green algae, emerald green algae, golden algae, flashing blue algae, red tides, brown tides, and jellyfish. Lots of jellyfish."
　
She compares our impacts on ocean life to those of the great geophysical changes that have occurred in the long history of the earth.

"Throughout the history of life on earth, major macroevolutionary events, such as mass extinctions and periods on intense evolutionary diversification have been linked to global-scale changes in environmental conditions….Today’s overfishing, pollution, and greenhouse gas emissions are comparable to the intense global warming, acidification, hypoxia [low oxygen], and mass extinctions throughout history….all at once."

Lest that last sentence be left to seem a bit overwrought, let’s pursue continued pollution and growing hypoxia to a final state and see what fate might possibly await us.

The continued increase in carbon dioxide in the atmosphere will cause the temperature to rise and will increase the amount of carbon dioxide absorbed into the ocean. This latter concentration will increase the acidity of the ocean and one of the effects will be the disappearance of things like lobsters and oysters as they will no longer be able to maintain their structures. This will take some time, but the effects are already measurable in terms of structural integrity of their shells.

The overall change in temperature of the oceans, felt mainly at the important surface layer, will continue to lower the oxygen content in the water. The continued pollution of our waterways, mostly with agricultural runoff containing fertilizers and animal waste, create vast dead zones—regions where oxygen is so depleted that essentially no life can be maintained.

"Eutrophication, an excess of nutrients in the ecosystem, occurs when these hypernutrified waters draining off the land are warmer and less salty than the seawater they are discharged into….This meeting creates stratification in the water column where the cooler, saltier, denser water stays on the bottom, and the warmer, fresher water floats on top."

This hypernutrified surface layer produces an overabundance of sea life, more than can be consumed. The result is that unconsumed phytoplankton and fecal matter sink to the bottom where aerobic bacteria consume them and use valuable oxygen in the process.

"Because the saltier layer is trapped below the surface layer and unable to touch air, the oxygen dissolving from the air cannot reach the bottom layer. The combination of stratification and decomposing organic matter create a zone of hypoxia (low oxygen) or anoxia (no oxygen) just above the seabed….Those creatures that can leave—those that can’t leave suffocate."

"As it worsens, the hypoxic area becomes one of the notorious ‘black bottoms’ with foul smelling sediments….Hypoxia leads to anoxia which leads to toxic hydrogen sulfide."

These dead zones that are created have a mechanism that exacerbates the situation and creates even greater nutrient growth and an increase in the size of the dead zone.

"Hypoxic bottom-water conditions cause seafloor sediments to release dissolved inorganic phosphorus. In the Baltic, the volume of phosphorus released from sediments is an order of magnitude larger than the amount flowing in from rivers. This stimulates a positive feedback cycle of phytoplankton blooms that drive hypoxia."

And then there is this final observation about dead zones:

"There are no known examples of recovery of large ecosystems from persistent hypoxia or anoxia….Once initiated, the low-oxygen condition appears to be permanent, even in the seasonal cases."

This is all consistent with the notion that we are causing irreversible damage to our oceans and our sea life. The expectation is that our coastlines will form a continuous boundary layer along the shores of our continents.

Wikipedia provides this information on dead zones.

"In March 2004, when the recently established UN Environment Programme published its first Global Environment Outlook Year Book (GEO Year Book 2003), it reported 146 dead zones in the world's oceans where marine life could not be supported due to depleted oxygen levels. Some of these were as small as a square kilometre (0.4 square miles), but the largest dead zone covered 70,000 square kilometres (27,000 square miles). A 2008 study counted 405 dead zones worldwide."

This chart, where red circles indicate the location and size of many of the dead zones, was also provided.

Recall that Gershwin told us that the ultimate result of anoxia was the production of the poisonous gas hydrogen sulfide. There are species of anaerobic bacteria that thrive in anoxic conditions. From Wikipedia:


"Sulfate-reducing bacteria can be traced back to 3.5 billion years ago and are considered to be among the oldest forms of microorganisms, having contributed to the sulfur cycle soon after life emerged on Earth."

"Sulfate occurs widely in seawater, sediment, or water rich in decaying organic material. Sulfate-reducing bacteria are common in anaerobic environments where they aid in the degradation of organic materials."

"The toxic hydrogen sulfide is a waste product of sulfate-reducing bacteria; its rotten egg odor is often a marker for the presence of sulfate-reducing bacteria in nature. Sulfate-reducing bacteria are responsible for the sulfurous odors of salt marshes and mud flats."

Gershwin also associated the term "mass extinction" with our current trajectory. Was that a bit of a reach? Perhaps not. Consider what is known of the greatest of the mass extinctions known as the Great Dying. Again from Wikipedia:

"It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It is the only known mass extinction of insects."

That event occurred about 250 million years ago. The geological record from that period contains evidence of widespread ocean anoxia and euxinia (the presence of hydrogen sulfide).

"A severe anoxic event at the end of the Permian would have allowed sulfate-reducing bacteria to thrive, causing the production of large amounts of hydrogen sulfide in the anoxic ocean. Upwelling of this water may have released massive hydrogen sulfide emissions into the atmosphere. This would poison terrestrial plants and animals, as well as severely weaken the ozone layer, exposing much of the life that remained to fatal levels of UV radiation. Indeed, biomarker evidence for anaerobic photosynthesis by Chlorobiaceae (green sulfur bacteria) from the Late-Permian into the Early Triassic indicates that hydrogen sulfide did upwell into shallow waters…."

"This hypothesis has the advantage of explaining the mass extinction of plants, which ought otherwise to have thrived in an atmosphere with a high level of carbon dioxide. Fossil spores from the end-Permian further support the theory: many show deformities that could have been caused by ultraviolet radiation, which would have been more intense after hydrogen sulfide emissions weakened the ozone layer."

One cannot prove that anoxic conditions leading to hydrogen sulfide production caused this particular event. However, the data indicates that considerable amounts of hydrogen sulfide can be produced by anoxic oceans. Waking up to oceans that reek of hydrogen sulfide may not kill you, but you might wish you were dead.

In any event, it is time to begin worrying more about what we are doing to our oceans. Gershwin could well be correct. The combined effects of pollution, global warming, and overfishing may have taken us to a state from which we can’t recover.