Oceanic anoxia or anoxic events are a part of Earth’s cycle. Anoxia refers to a lack of oxygen. Geological records show it has occurred many times in the past and coincides with several mass extinctions. Ocean Anoxia has been a naturally occurring phenomenon in Earth’s history but over the past 130 years’ anthropogenic forces are contributing to current ocean oxygen depletion.
Oceanic anoxic events commonly occurred during periods of very warm climate characterized by high levels of carbon dioxide (CO2), and mean surface temperatures in excess of 25 °C. These events may have been responsible for mass extinctions of marine organisms in the Mesozoic era. Most oceanic anoxic events last for less than a million years, before a full recovery is made. An economic consequence of oceanic anoxic events is that it has helped produce most of the world’s petroleum and natural gas reserves (Kump). The accumulation and preservation of organic matter and its subsequent conversion into fossil fuels has taken millions of years to occur with proper conditions established by mother nature.
The anthropogenic interventions have replaced mother nature and has become a major contributing factor of Ocean Anoxia. Global climate change produces many effects from increase weather events, such as stronger hurricanes, to increase surface and ocean temperatures. As warmer water expands it raises sea level. Changing composition of the oceans has caused increased carbon dioxide levels in the oceans which in turn are acidifying larger areas and displacing oxygen levels. Due to human activity in industrial and agricultural fields the world’s oceans are experiencing declines in dissolved oxygen. Usually associated with sewage discharges and agricultural fertilizer runoff, the problem now is intensified by climate change (Limburg.). If left unimpeded, this decline will result in losses of marine life, biodiversity, and poor water quality.
The process of anoxic events is very complex. The following is a very simplified version from an article provided by Karen Limburg, a Professor of Environmental and Forest Biology, from the State University of New York. The aquatic environment holds dissolved gases; oxygen is one of them. Add in aquatic plants, a CO2 source, nutrients and light, and the resulting photosynthesis creates biomass and oxygen. Organisms that consume this plant matter also use oxygen further depleting oxygen levels. Fertilizer, pollutants, and CO2 man made emissions stimulate the growth of aquatic plants. This may cause algae to develop. As algae decays microbes draw down the dissolved oxygen. As temperature increases warmer water holds less oxygen leading to stratification (the separation of water into layers) in which the lower layers of cold deeper waters lose even more oxygen. Few organisms can survive under low oxygen conditions.
“Dead Zones” have developed across the world which are areas that have little to no oxygen in the water. Marine life is minimal if not non-existent in these areas. Dead zones exist off the East Coast of the United States, the Black Sea, and in the Gulf Coast just to name a few. As global warming increases ocean temperatures, deeper ocean levels also lose oxygen (Diaz). The Baltic Sea has been experiencing increasing anoxic conditions since the 1940s encompassing an area almost three times larger than the dead zone located off the coast of Louisiana (Casini, et al.).
One of the effects of ocean deoxygenation is smaller fish. This reduction in fish size will have large impacts on the fishing industry. With much of the world consuming fish, and some as their only food source, more fish will be required to meet the previous requirements when fish were larger. In some areas with lower ocean oxygen levels, fish who in the past encompassed a large geographical area see their available habitat shrink. These smaller fishing grounds make it easier for fishermen to farm them and can greatly affect their ability to adequately reproduce (Bopp et al.). As ocean oxygen levels continue to decrease and become non-existent as seen in many areas, fish simply die off. Evidence has been seen world-wide where millions of tons of fish wash up on shores.
Although the oceans have experienced great oxygen declines in the past, there is clear evidence that human actions, notably higher water temperatures due to man-made CO2 emissions and continued pollution from agricultural and industrial areas, are a contributing factor for present changes. The solution may appear simple, but the path forward is far from it. Reducing pollution and CO2 emissions requires a total renovation of how our society here and abroad conduct business.
Ocean deoxygenation is already having drastic effects on our fishing industry. A 2014 United Nations report estimated 1.3 billion tons of fish are lost every year. Fish is consumed all over the world not only by people but by animals. If this issue is not reversed and we slowly lose the oceans, countless of species will be irreparably affected if not lost. We have the duty to defend our planet and make this issue public. The call to action must be made to our countries governments and private businesses to seek more eco-friendly methods of agricultural and industrial approaches in meeting human demands. Renewable sources of energy must be accepted as the norm.
We can no longer continue with our current CO2 emissions and pollution methods. Contact our government representatives and demand proper legislation be introduced and signed that can be enforced through criminal and severe financial consequences for those who damage our environment. Dead zones are popping up all over the world affecting countless species of fish, the environment, and the people. If we do not take action now, we may lose all marine life.
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