Lecture Ocean Acidification

Transcription

1 Lecture Ocean Acidification

2 What is Ocean Acidification? Since the beginning of the Industrial Revolution, the ph of surface ocean waters has fallen by 0.1 ph units. Moving the ocean's ph from to a current ph of 8.069, which means the ocean is about 30% more acidic now than it was in 1751 (SCOR 2009). Since the ph scale, like the Richter scale, is logarithmic, this change represents approximately a 30 percent increase in acidity.

3 Acidity and Alkalinity Acid releases a hydrogen ion (H+) when dissolved in water. Alkaline (or base) releases a hydroxide ion (OH-) in water Pearson Education, Inc.

4 Acidity is commonly measured using the ph scale. Pure water has a ph of about 7, which is considered neutral. A substance with a ph less than 7 is considered to be acidic, while a substance with a ph greater than 7 is considered to be basic or alkaline. The lower the ph, the more acidic the substance. Like the well-known Richter scale for measuring earthquakes, the ph scale is based on powers of 10, which means a substance with a ph of 3 is 10 times more acidic than a substance with a ph of 4. For more

5 ph Scale Measures hydrogen ion concentration Low ph value, acid High ph value, alkaline (basic) ph 7 = neutral Pure water 2011 Pearson Education, Inc.

6 Carbonate Buffering System Ocean ph averages 8.1 and ranges from 8.0 to 8.3. Buffering keeps the ocean from becoming too acidic or too basic. Precipitation or dissolution of calcium carbonate, CaCO 3, buffers ocean ph. Oceans can absorb CO 2 from the atmosphere without much change in ph Pearson Education, Inc.

7 Fig. 6-17

8 Ocean Acidification 2011 Pearson Education, Inc.

9 2011 Pearson Education, Inc.

10 The extent of floating sea ice in the Arctic Ocean, as measured at its annual minimum in September, showed a steady decline between 1980 and 2009.Source: National Snow and Ice Data Center, graph compiled by Secretariat of the Convention on Biological Diversity (2010) Global Biodiversity Outlook 3, May

11 Source: John Bruno, It s not climate change, it s ocean change!, Climate Shifts, July 12, 2010 The implications of this is further explained with Inter Press Service s freezer analogy: The world s northern freezer is on rapid defrost as large volumes of warm water are pouring into the Arctic Ocean, speeding the melt of sea ice.

12 Katharina D. Six, Silvia Kloster, Tatiana Ilyina, Stephen D. Archer, Kai Zhang, Ernst Maier- Reimer. Global warming amplified by reduced sulphur fluxes as a result of ocean Climate change: Ocean acidification amplifies global warming Observations of reduced DMS concentration with decreasing seawater ph from different mesocosm experiments.

13 the relationship between changes in ocean carbon dioxide levels (measured in the left column as a partial pressure and acidity (measured as ph in the right column).

14 Between the 1880s and the most recent decade ( ). A negative change represents a decrease in saturation The lower the saturation level, the more difficult it is for organisms to build and maintain their skeletons and shells.. Data source: Woods Hole Oceanographic Institution, 2016

15 Carbon dioxide levels have risen in response to increased carbon dioxide in the atmosphere, leading to an increase in acidity (that is, a decrease in ph) (see Figure 1). Since the 1880s, increased carbon dioxide has led to lower aragonite saturation levels in the oceans around the world, which makes it more difficult for certain organisms to build and maintain their skeletons and shells (see Figure 2). The largest decreases in aragonite saturation have occurred in tropical waters (see Figure 2); however, decreases in cold areas may be of greater concern because colder waters typically have lower aragonite saturation levels to begin with.

16 Biological Impacts Dramatic effect on some calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton

17 National Geographic Images. The pteropod, or sea butterfly, is a tiny sea creature about the size of a small pea. Pteropods are eaten by organisms ranging in size from tiny krill to whales and are a major food source for North Pacific juvenile salmon. Pteropod Limacina Helicina. Courtesy of Russ Hopcroft, UAF.

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19 future atmospheric carbon dioxide will be high enough to lower ocean surface ph to 7.8 by the year 2100 (Royal Society 2008). laboratory studies suggest a ph about this low could dissolve coral skeletons and may cause reefs to fall apart (Fine and Tchernov 2006).

20 Coral Reefs in Decline 30% healthy today, 41% healthy in 2000 One third of corals high risk of extinction Humans greatest threat Other threats Hurricanes Global warming Coral bleaching Floods Tsunami 2011 Pearson Education, Inc.

21 Coral bleaching Coral bleaching occurs when symbiotic zoothanthellae algae is removed or expelled Associated with high water temperatures Figure 15B

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