OUR HUMAN IMPACT ON THE WORLD’S OCEANS
The global oceans are the largest natural reservoir of carbon dioxide. They absorb about one-third of the carbon dioxide we humans spew into the atmosphere every year. Although this process is extremely slow, taking hundreds to thousands of years, once dissolved, a carbon atom can remain in the water for decades or centuries depending on the depth in the ocean in which it is located. However, anthropogenic carbon dioxide now penetrates the whole water column of the North Atlantic Ocean.
Moreover, there’s a strong possibility that dissolved carbon dioxide in the ocean’s surface waters will double over its pre-industrial levels by mid-century and will be accompanied by even greater acidity as well as by a decrease in the carbonate ion. When carbon dioxide reacts with seawater, it produces carbonic acid, which can be thought of as the soda-water effect. This change in seawater chemistry is having profoundly negative effects on the calcium-secreting organisms in the world’s oceans because they depend on calcium carbonate for the production of their shells (mollusks, including planktonic mollusks, and marine algae) and skeletons (corals).
On a global scale, the alterations in surface-water chemistry from the anthropogenic deposition of nitrogen, sulfur, and dissolved inorganic carbon are relatively slight compared with the acidification caused by the oceanic uptake of anthropogenic carbon dioxide. The impacts are more substantial in coastal waters, however, than in the deep ocean. In coastal areas, the ecosystem responses to acidification will have severe implications for people, especially those who rely on the seas of the world for food.
These changes are already sending ripples throughout the marine food web—from the microscopic plankton to the plankton-feeding whales and all life in between—and will only increase over time. As the ocean gets warmer and more acidic, the amount of dissolved oxygen will diminish accordingly, which will magnify the severity of the oceanic dead zones (oxygen-deprived areas), as will the availability calcium carbonate required by coral and other calcium-secreting organisms.
In fact, these species already have a reduced ability to produce their protective shells (oysters, snails, and others) and supportive skeletons (coral). In addition, the increase in carbonic acid is even now beginning to dissolve the shells and skeletons once they are produced, which is making them increasingly susceptible to wear and erosion. Decreased calcification will no doubt compromise survival of these organisms and will shift marine flora and fauna toward non-calcifying species. For example, the common periwinkle (a small marine snail) normally grows extra-thick shells when living among crabs, but the snail’s ability to produce a thicker-than-normal protective shell is disrupted if the water is too acidic.
“You don’t have to believe in climate change to believe that this is happening,” says Joanie Kleypas, an oceanographer with the University Corporation for Atmospheric Research in Boulder, Colorado. “It’s pretty much simple thermodynamics.” According to Kleypas, “Acidification is more frightening than a lot of the climate change issues” because it’s much harder to turn around. “It’s a slow-moving ship, and we’re all trying to row with toothpicks.”1
Although the oceans of the world seem immutable, no area is unaffected by human influence. In fact, 41 percent of the oceans have been seriously degraded by multiple human factors; to name a few: overfishing; fishing commercially a mile below the surface of the water with high-tech gear; pollution; commercial shipping; military sonar; offshore oil exploration, extraction, and the inevitable spills. Less than 4 percent of the oceans can be classified as areas of very low anthropogenic impact, and they are mainly near the poles.2
During the nineteenth century, commercial sealers hunted Antarctic fur seals to near extinction. What’s more that slaughter was followed in the twentieth century by the widespread killing of krill-eating baleen whales, which enabled the tiny crustaceans to proliferate essentially unchecked, until there is today a surplus of krill in the Southern Ocean.3 Clearly, the overexploitation of the Antarctic waters has left its mark, even if that human signature is faint by today’s standards.
As we humans attack marine life, we alter how the oceanic life relates to climate change.4 Consider, for example, that overexploiting of the large, predatory marine fishes, such as sharks and tuna, allows the populations of smaller, plankton-feeding fishes to proliferate. At some point, their numbers become large enough to dramatically reduce the amount of phytoplankton and thus the ocean’s ability to absorb atmospheric carbon dioxide; in turn, these changes affect global warming.5
That said, curbs on fishing, such species as big-eye tuna and yellow-fin tuna, until their populations are larger than those required to maintain a sustainable yield could, within biological limits, lead to maximum profits from fisheries.6 But then, warming oceans affect the major wind patterns, which affect the direction of ocean currents, which is shifting dead zones in the oceans, causing them to grow,7 which in turn affect the distribution of ocean fishes, as well as the global climate.
According to Alex Rogers, a professor of conservation biology at the University of Oxford, UK, “The speed of change, particularly related to climate change, is so great there simply isn’t time for marine life to adapt to these new conditions. When we’ve seen mass extinctions in the past they’ve been associated with large disturbances in the carbon system of the oceans. That’s what we’re bringing about through our own actions today.” For example, 50 percent of the sharks in the Mediterranean region are under the threat of extinction.8
Although the tradeoff of human activities in the ocean may at times cancel each other out, many are negatively synergistic, which means the cumulative effects are compounding. To whit, the resilience of many marine ecosystem has already been so eroded their increased vulnerability to climate change will decrease their capacity to recover through biophysical adaptation. For example, self-reinforcing feedback loops embodied in overfishing affects the overgrazing of the phytoplankton by small fishes, which increased the carbon dioxide in the water, which in turn increased oceanic acidification, which in turn causes the corals to bleach, and could lead to the virtual extinction of the most diverse marine ecosystems in the world’s oceans.9
The challenge for humanity is that whatever happens in the oceans of the world affects virtually all of the global feedback loops because the oceans are not only the ultimate source of the world’s fresh water but also a primary arbitrator of the global climate. And, we humans continue to be the responsible party.10 In other words, we—through our uncontrolled behavior—are the authors of our own troubles, as well as those we increasingly bequeath the generations to come.
Related Posts:
• Meeting The Ocean (Oceanic Extinctions—Part 1)
• Resource overexploitation (Oceanic Extinctions—Part 2)
• Lessons We Need to Learn For the Sake of All Generations (Oceanic Extinctions—Part 4)
• The Ocean, Mother Of All Waters
• Principle 1: Everything is a relationship
• Principle 4: All systems are defined by their function.
• Principle 6: All relationships are self-reinforcing feedback loops.
• Principle 11: All systems have cumulative effects, lag periods, and thresholds.
ENDNOTES
1. The preceding discussion of ocean acidification is based on: (1) Helmuth Thomas and Venugopalan Ittekkot. Determination of Anthropogenic CO2 in the North Atlantic Ocean Using Water Mass Ages and CO2 Equilibrium Chemistry. Journal of Marine Systems 27 (2001): 325–336; (2) Jonathan Shaw. The Great Global Experiment: As Climate Change Accelerates, How Will We Adapt to a Changed Earth Harvard Magazine 105 (2002): 34–43, 87–90; (3) Kathy Tedesco, Richard A. Feely, Christopher L. Sabine, and Cathrine E. Cosca. Impacts of Anthropogenic C02 on Ocean Chemistry and Biology. NOAA Archive of Spotlight Feature Articles 2005, http://www.oar.noaa.gov/spotlite/spot_gcc.html; (4) Lisa Stiffler. Research in Pacific Shows Ocean Trouble. Seattle Post Intelligencer March 31, 2006; (5) Ruth Bibby, Polly Cleall-Harding, Simon Rundle, and others. Ocean Acidification Disrupts Induced Defences in the Intertidal Gastropod Littorina littorea. Biology Letters 3 (2007): 699–701; (6) Scott C. Doney, Natalie Mahowald, Ivan Lima, and others. Impact of Anthropogenic Atmospheric Nitrogen and Sulfur Deposition on Ocean Acidification and the Inorganic Carbon System. Proceedings of the National Academy of Sciences 104 (2007): 14580–14585; (7) Rosane Gonçalves Ito, Bernd Schneider, and Helmuth Thomas. Distribution of Surface fCO2 and Air-Sea Fluxes in the Southwestern Subtropical Atlantic and Adjacent Continental Shelf. Journal of Marine Systems 56 (2005): 227–242; (8) J. C. Blackford and F. J. Gilbert. pH Variability and CO2 Induced Acidification in the North Sea. Journal of Marine Systems 64 (2007): 229–241; (9) Igor P. Semiletov, Irina I. Pipko, Irina Repina, and Natalia E. Shakhova. Carbonate Chemistry Dynamics and Carbon Dioxide Fluxes across the Atmosphere-Ice-Water Interfaces in the Arctic Ocean: Pacific Sector of the Arctic. Journal of Marine Systems 66 (2007): 204–226; and (10) O. Hoegh-Guldberg, P. J. Mumby, A. J. Hooten, and others. Coral Reefs under Rapid Climate Change and Ocean Acidification. Science 318 (2007): 1737–1742.
2. Benjamin S. Halpern, Shaun Walbridge, Kimberly A. Selkoe, and others. A Global Map of Human Impact on Marine Ecosystems. Science 319 (2008): 948–952.
3. Steven D. Emslie and William P. Patterson. Abrupt Recent Shift in 13C and 15N Values in Adélie Penguin Eggshell in Antarctica. Proceedings of the National Academy of Sciences 104 (2007): 11666–11669.
4. Phillip S. Levin, Elizabeth E. Holmes, Kevin R. Piner, and Chris J. Harvey. Shifts in a Pacific Ocean Fish Assemblage: The Potential Influence of Exploitation. Conservation Biology 20 (2006): 1181–1190.
5. (1) Ransom A. Myers and Boris Worm. Extinction, Survival or Recovery of Large Predatory Fishes. Philosophical Transactions of the Royal Society of London: Biological Sciences 360 (2005): 13–20; (2) Peter Ward and Ransom A. Myers. Shifts in Open-Ocean Fish Communities Coinciding with the Commencement of Commercial Fishing. Ecology 86 (2005): 835–847; and (3) Kenneth T. Frank, Brian Petrie, Jae S. Choi, and William C. Leggett. Trophic Cascades in a Formerly Cod-Dominated Ecosystem. Science 308 (2005): 1621–1623.
6. (1) Benjamin S. Halpern, Karl Cottenie, and Bernardo R. Broitman. Strong Top-Down Control in Southern California Kelp Forest Ecosystems. Science 312 (2006): 1230–1232; (2) Chris L. J. Frid, S. Hansson, S. A. Rijnsdorp, and S. A. Steingrimsson. Changing Levels of Predation on Benthos as a Result of Exploitation of Fish Populations. Ambio 28 (1999): 578–582; (3) Chris L. J. Frid, Odette A. L. Paramor, and Catherine L. Scott. Ecosystem-based Management of Fisheries: Is Science Limiting? Journal of Marine Science 63 (2006): 1567–1572; (4) Shelley C. Clarke, Jennifer E. Magnussen, Debra L. Abercrombie, and others. Identification of Shark Species Composition and Proportion in the Hong Kong Shark Fin Market Based on Molecular Genetics and Trade Records. Conservation Biology 20 (2006): 201–211; and (5) R. Q. Grafton, T. Kompas, and R. W. Hilborn. Economics of Overexploitation Revisited. Science 318 (2007): 1601.
7. (1) D. Pauly and V. Christensen. Primary Production Required to Sustain Global Fisheries. Nature 374 (1995): 255–257; (2) John A. Barth, Bruce A. Menge, Jane Lubchenco, and others. Delayed Upwelling Alters Nearshore Coastal Ocean Ecosystems in the Northern California Current. Proceedings of the National Academy of Sciences 104 (2007): 3719–3724; (3) F. Chan, J. A. Barth, J. Lubchenco, and others. Emergence of Anoxia in the California Current Large Marine Ecosystem. Science 319 (2008): 920; and (4) Ryan R. Rykaczewski and David M. Checkley Jr. Influence of Ocean Winds on the Pelagic Ecosystem in Upwelling Regions. Proceedings of the National Academy of Sciences 105 (2008): 1965–1970.
8. Christina Caron. Impending Disaster: Marine Species Face Mass Extinction, Experts Say. http://abcnews.go.com/Technology/marine-species-face-mass-extinction-report/story?id=13893627. (June 22, 2011)
9. (1) Georgi M. Daskalov, Alexander N. Grishin, Sergei Rodionov, and Vesselina Mihneva. Trophic Cascades Triggered by Overfishing Reveal Possible Mechanisms of Ecosystem Regime Shifts. Proceedings of the National Academy of Sciences 104 (2007):10518–10523 and (2) Alex D. Rogers and Dan. D’a Laffoley. International Earth System Expert Workshop On Ocean Stresses And Impacts. Summary Report. IPSO Oxford, 18 Pp. 2011.
10. Arthur Max. Greenhouse Gas Emissions Hitting Record Highs. http://abcnews.go.com/Business/wireStory?id=13764654. (June 5, 2011)
Text © by Chris Maser 2011. All rights reserved.
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