Many students have heard about ocean acidifcation as a result of climate change. This results from the dissolving of carbon dioxide in the ocean due to the ocean’s ability to act as a large-scale CO2 sink; however, this is not without consequence as carbon dioxide lowers the pH of aqueous environments. These graphs suggests that so much CO2 is entering the ocean that the innate buffering systems of the ocean (i.e. bicarbonate buffering system) is being surpassed resulting lowered pH. Both of these graphs were prepared as part of the Fourth Assessment of the Intergovernmental Panel on Climate Change (IPCC) which was published in 2007. The left series of graphs show changes in carbon dioxide at three different oceanic location and pH is those same three locations. What should be highlighted to the students is the relatively consistent response at all three locations. The graph/map on the right shows historic changes in ocean pH from 1700s to 1990s. Unfortunately, this graph does not show these changes over time as it would be interesting to see when a certain percentage of the chain occurred – that is to say does the rate of change increase after industrialization for example. Nonetheless, students should be able to see over the last 200 years all oceans have become increasingly acidic.
1.Have students brainstorm other mechanisms that could create changes in ocean acidity.
2.Have students research range of tolerance with respect to pH for different oceanic organisms (e.g. corals, invertebrates, kelp, mammals).
3.Have students research the ecological concept of source-sink. For example, soil respiration (by soil microorganisms) is a source of carbon dioxide to the atmosphere while the oceans’ ability to dissolved atmospheric carbon dioxide is a sink. Could the ocean change from a carbon dioxide sink to a source? What would happen to rates of global climate change if the source-sink dynamic of the Earth’s oceans did indeed change?