State of the World 2015 by The Worldwatch Institute

Author:The Worldwatch Institute
Language: eng
Format: epub
Publisher: Island Press

NOAA

Marine debris on a beach in Kanapou Bay, Hawaii.

Once released into the ocean, plastic debris is transported widely by tides and currents, and ingested by mammals, fish, birds, and invertebrates. Upon ingestion, microplastics may release harmful chemicals and toxic additives such as plasticizers, flame retardants, and antimicrobial agents into biota. Ingestion of even small quantities of microplastics has been shown to interfere with physicological processes in marine worms, affecting their ability to store energy.21

Climate change may amplify this threat in unexpected ways. As sea ice forms, it concentrates natural particulates from the water column. A recent study found that concentrations of microplastics in Arctic sea ice, even in remote locations, can exceed by several orders of magnitude the concentrations found in notoriously polluted surface waters like the Pacific gyre. As sea ice melts in response to warming temperatures, these microplastics could be released into the sea, posing additional threats to marine ecosystems.22

Ocean acidification. As a natural carbon sink, the oceans have absorbed about a quarter of all anthropogenic (human-caused) CO2 emissions released into the atmosphere to date, with significant impacts on ocean chemistry. When seawater absorbs CO2, a series of chemical reactions reduces the water’s pH (i.e., increases its acidity), lowers the concentration of carbonate ions, and reduces the saturation level of calcium carbonate minerals. Because calcium carbonate forms the basis for shells and skeletal structures in many marine organisms (for example, in oysters, clams, corals, and sea urchins), this poses a distinct threat to marine life and the food web. Elevated concentrations of CO2 also have been found to interfere with neurological processes in fish, resulting in behavioral changes that may impede survival.23

Since the Industrial Revolution, the acidity of open-ocean surface waters has increased by about 30 percent. If emissions continue at current levels, ocean acidity in surface waters could increase by almost 150 percent by 2100, creating a marine environment unlike anything that has existed in the past 20 million years. Although ocean acidification can be buffered through natural processes, including erosion and the dissolution of calcium carbonate from sediments, these longer-term mechanisms likely are unsuited to cope with the rapidly rising acidity resulting from anthropogenic CO2 emissions.24

The rate of acidification varies geographically. In the polar regions, acidification can be exacerbated by excess precipitation or ice melt—both projected to increase as a result of climate change—because these processes reduce salinity and decrease the concentration of substances needed to buffer the acidification process. In addition, high-latitude oceans naturally contain lower concentrations of calcium carbonate minerals and therefore are more vulnerable to ocean acidification because additional losses of calcium carbonate impose a greater relative change. Individual species’ responses to ocean acidification vary as well, with growth stimulated in some animals and hampered or unaffected in others. Overall, an organism’s ability to withstand changes in acidity depends on other factors that support overall resilience, including quality of food and fitness.25

The cumulative threat posed by climate change to marine organisms and ecosystems is not yet fully understood. Part of the challenge in understanding climate impacts is that distinct climate-related factors often reinforce each other.

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