The levels of dissolved oxygen in oceans worldwide is a concern for environmentalists, capitalists, and beachgoers alike. When oxygen levels get so low that they are considered apoxic, the area is considered a dead zone, an area from which marine life flees to more oxygenated water. In saltwater, salinity levels determine how much oxygen can dissolve in the water. The higher the salinity, the lower the dissolved oxygen levels (static.fishersci.com). Compared to the Atlantic Ocean, for example, the Pacific Ocean in general has a lower salinity. The water closest to Japan is moderately salty. (aquarius.umaine.edu)
(Image retrieved from aquarius.umaine.edu)
With this information, we know that the water in oceans has less oxygen than fresh water. In Tokyo Bay, much of the oxygen in the water comes from estuaries that feed into the bay, helped along by wind patterns that move the surface water (Sato, Nakayama, & Furukawa 2012). Strong winds bring more oxygen to the bay, as do floods from the rivers.
In Chapter 5 of the textbook, we read about hypoxia in Chesapeake Bay, which was caused by overharvesting of oysters. Scientists who study Tokyo Bay are looking less to marine life as a cause. In one study the bottom of the bay was dredged, and the sediment was analyzed to determine whether the water was more anoxic or less anoxic than it was 30 years ago (Shozugawa, Hara, Kanai, & Matsuo 2011). The finding was that the bay is growing less anoxic over time, which is good news for Tokyo Bay.
The research that is being done on this topic is certainly a step forward for marine ecology, and for environmental science. The information gathered from hypoxic regions provides a variety of perspectives and ideas, such as the study of marine life’s effect on dissolved oxygen levels, as well as the effects of estuarine contributions and wind factors. To effect change on the environment around us, which we humans are also a part of, we must first take those steps to understand the workings of the natural processes that kept the world going for millennia before we arrived. For instance, scientists have come to know that hypoxia is more common in Tokyo Bay in summer than it is the rest of the year. With this information, we know that a study of the bay during the summer would provide the most accurate findings on the causes of hypoxia and anoxia in Tokyo Bay. From knowing the causes scientists can begin making proposals for the mitigation of hypoxia, like in the Chesapeake Bay example.
(Image retrieved from http://www.bibliotecapleyades.net)
The ocean is our largest reserve of water, though it may not be used as drinking water or for daily use in the home. It is also an invaluable resource, because of the diversity of life that it supports. We need our oceans, and if issues of hypoxia continue, they are going to need us.
References
Blumenthal, Les. (2010, March 8). Growing Low-Oxygen Levels in Oceans Worry Scientists. McClatchy Newspapers. Retrieved from http://www.bibliotecapleyades.net/ciencia/ciencia_earthchanges14.htm
http://aquarius.umaine.edu/cgi/ed_aq_datatool.htm
Sato, Chizuru, Nakayama, Keisuke, & Furukawa, Keita. (2012). Contributions of wind and river effects on DO concentrations in Tokyo Bay. Estuarine, Coastal, and Shelf Science 109, 91-97. Retrieved from http://www.sciencedirect.com/science/article/pii/S0272771412001904
Shozugawa, Katsumi, Hara, Naoki, Kanai, Yutaka, & Matsuo, Motoyuki. (2012) Evidence for a weakening ‘dead zone’ in Tokyo Bay over the past 30 years. Hyperfine Interactions, 207 (1-3), 89-95. Retrieved from http://link.springer.com/article/10.1007/s10751-011-0463-9#page-1
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