Intro to Environmental Science

Unit 4 Graphing Exercise (watch lecture 4.8 first)

Atmospheric Carbon Dioxide and Seawater pH

Marine ecosystems are facing a variety of problems, with one of them being Ocean Acidification, as the pH of the world's oceans has been falling due to the use of fossil fuels. Water with a pH of 7 is considered neutral, but seawater has a higher pH and is thus basic (also called alkaline) and organisms that live in the oceans have adapted to this basic pH over millions of years. If it falls, then it moves towards being acidic rather than basic, and that's the problem.

A basic pH (that stays between approximately 8.0 and 8.4) is especially important to organisms like corals, clams, snails, and other animals that produce calcium carbonate skeletons, shells, spines, etc. primarily for two reasons. At a pH significantly lower than 8.0, calcium carbonate simply cannot be produced by organisms. The chemical reactions used to produce it will not work. And, at a lower pH, calcium carbonate will actually dissolve into sewater, too. So, if the pH falls more than a few tenths of a point lower than it is now, some organisms will not be able to make calcium carbonate structures, and even if they can, the structures may be dissolved away as fast as they are produced. Either is deadly, as this would be the equivalent of a person being perfecetly healthy - except they wouldn't be able to make any bones. Obviously, that would make it impossible to survive.

The burning of fossil fuels is the main problem, because we add billions of tons of CO2 to the atmosphere every year by doing so. Much of this CO2 dissolves into the oceans, and some of it combines with water molecules (H2O) and turns into carbonic acid (H2CO3). This makes the overall pH fall, and as our activities continue to produce more CO2, the pH will continue to fall.

Do note that the oceans aren't actually acidic, as pointed out above, and are still a long way from even being neutral. However, they are closer to being acidic, which is why this is called Ocean Acidification. As an analogy, if the average temperature of very cold area was to warm up a few degrees due to Global Warming, it would still be cold, but we would say it has warmed.

With that covered, in this graphing exercise you'll be able to visualize the rapid increase in the concentration of CO2 in the atmosphere, and the corresponding fall of the oceans' pH, too. So, use the data below to complete the blank line graph on the next page, and submit the graph by the posted deadline. Remember to watch the lecture on making graphs before making yours, and to follow the submission guidelines.

	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005
Carbon Dioxide	361	363	364	366	368	370	371	373	376	377	379
Surface Water pH	8.095	8.093	8.092	8.089	8.087	8.085	8.084	8.082	8.079	8.078	8.076

	2006	2007	2008	2009	2010	2011	2012	2013	2014	2015
Carbon Dioxide	382	383	385	387	389	390	393	395	397	400
Surface Water pH	8.073	8.072	8.070	8.068	8.066	8.065	8.062	8.060	8.058	8.055

Unit 4 Graphing Exercise