An Ecological Perspective (BIOL 346)

1. An Ecological Perspective (BIOL 346) Talk Ten: Ocean acidification

2. So, what is it? • The ongoing decrease in the pH of the Earth's oceans, caused by the uptake of carbon dioxide (CO2) from the atmosphere. • An estimated 30–40% of the carbon dioxide released by humans into the atmosphere dissolves into oceans, rivers and lakes. • To achieve chemical equilibrium, some of it reacts with the water to form carbonic acid. • Some of these extra carbonic acid molecules react with a water molecule to give a bicarbonate ion and a hydronium ion, thus increasing ocean "acidity" (H+ ion concentration).

3. So, what is it? • Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14, representing an increase of almost 30% in H+ ion concentration in the world's oceans. • Earth System Models project that within the last decade ocean acidity exceeded historical predictions • Could undermine the functioning of marine ecosystems and many ocean goods and services Estimated change in sea water pH caused by human created CO2 between the 1700s and the 1990s, from the Global Ocean Data Analysis Project (GLODAP) and the World Ocean Atlas

4. The total amount of any gas seawater can absorb depends on temperature and salinity Salinity is a measure of the dissolved salt content of water Remember this relationship! Temperature or Salinity Amount of gas seawater can absorb How much CO2 can the ocean absorb? Increases in temperature and  salinity can decrease the amount of gas seawater can absorb.

5. From the wikimedia free licensed media file repository

6. Life on Earth would not be possible without water Its chemical and physical properties actually defy some fundamental laws of physicsAlmost all biochemical reactions require water!

7. How does water support life? • Water is cohesive • Water can moderate temperature of surroundingenvironment • Ice floats • Versatility of water as a solvent From the wikimedia free licensed media file repository

8. Water

9. Water has hydrogen bonding potential • H-bonds are non-covalent, weak interactions • H2O is both a Hydrogen donor and acceptor • One H2O can form up to four H-bonds

10. Water • (A) Hydrogen bonds between water molecules results in local aggregations of water molecules • (B) Theses are very short lived, break up rapidly to form more random configurations • Due to temperature variations in water

11. Density • Another property of water is density during phase changes. • The density of most substances increases when a liquid becomes a solid. Solid water is actually less dense than liquid water. • It is for this reason that ice floats. • The fact that ice floats is essential for the survival of many aquatic ecosystems and ultimately life on Earth. Hydrogen bond Ice Liquid water Hydrogen bonds constantly break and re-form Stable hydrogen bonds From the wikimedia free licensed media file repository

12. Capillary Action & Surface tension • Cohesion of water causes capillary attraction, which is the ability of water to move upward in small spaces. • Cohesion makes it possible for water to move up the fibers of a plant. • In addition, it moves water upwards in soil. • Allows water to be taken into human cells attached to other molecules • Cohesion of water also causes surface tension, water's invisible skin which allows water striders to walk on water From the wikimedia free licensed media file repository

13. pH and buffers • Measure of the acidity or basicity of an aqueous solution. • Solutions with a pH less than 7 are said to be acidic • Solutions with a pH greater than 7 are basic or alkaline. • Pure water has a pH very close to 7 • Acid • A chemical compound that donates H+ ions to solutions. • Base • A compound that accepts H+ ions and removes them from solution. • Remember H3O+ and OH-? • The H3O+ donates H+ to a solution and the OH- removes H+ from a solution • If an equal number of these ions are present in a solution the pH will not change as it is said to be buffered.

14. The pH scale • To describe the acidity of a solution, we use the pH scale. • Acids have a low pH, so they have a high concentration of H+ • Bases have a high pH, so they have a low concentration of H+ Used with permission from purewaterproducts.com

15. The ocean absorbs carbon dioxide from the atmosphere • Human activities release carbon dioxide into the atmosphere • Too much carbon dioxide in the ocean has the potential to harm marine organisms and ecosystems

16. How is atmospheric CO2 responsible for ocean acidification? When CO2 dissolves in seawater, carbonic acid is produced via the reaction: This carbonic acid dissociates in the water, releasing hydrogen ions and bicarbonate: The increase in the hydrogen ion concentration causes an increase in acidity, since acidity is defined by the pH scale, where pH = -log [H+] (so as hydrogen increases, the pH decreases). This log scale means that for every unit decrease on the pH scale, the hydrogen ion concentration has increased 10-fold. One result of the release of hydrogen ions is that they combine with any carbonate ions in the water to form bicarbonate: This removes carbonate ions from the water, making it more difficult for organisms to form the CaCO3 they need for their shells.

17. All CaCO3 shells are not created equal Aragonite (orthorhombic) Calcite (hexagonal) 10 g 8 g Calcite Calcite Decreased ocean pH (more acidic water) 10 g Aragonite Aragonite 5 g

18. “Battle” for carbonate! • Organisms must use more energy or make less hard part material • Existing hard parts dissolve (chemical reaction goes “the wrong way”) From the wikimedia free licensed media file repository

19. Hgm, • dgdfg

20. First-sale revenues from U.S. commercial fisheries totaled about $4 billion. • Four groups of animals contributed almost equally to that total. • Two groups are calcifiers, which means they make shells, spines, or exoskeletons out of calcium carbonate: crustaceans (lobsters, crabs, shrimp) and mollusks (clams, oysters, mussels, scallops, and other non-crustacean calcifiers). • The other two groups are animals that prey on calcifiers (such as flounder and octopus) and top predators that eat the calcifiers’ predators (such as salmon and tuna). • Of these groups, the mollusks appear most vulnerable to direct effects of ocean acidification. But a decline in those species could cause problems for predators above them on the food chain.dvsdv Used with permission from the Woods Hole Oceanographic Institution

21. Ocean acidification: Impacts on individual marine organisms Reduced fertilization of gametes in corals and other marine organisms • Deformed flagellum in sperm that impacts their swimming • Fitness effect: lower population growth Natural range in the ocean Normal Acidic Albright et al. 2010

22. Ocean acidification: Impacts on individual marine organisms Reduced hearing ability in anemone fish (clown fish) larvae • Deformed morphology of CaCO3 fish ear bones (otoliths) • Disruption of acid-base balance in neuro-sensory system • Fitness effect: lower survival due to higher predation. From the wikimedia free licensed media file repository Simpson et al. 2011

23. Ocean acidification: Impacts on ecological communities Tropical Oceans Predictions: • Corals will become increasingly rare • Algae will become more abundant • Because coral reefs support so many animals, biodiversity will decline Hoegh-Guldberg et al. 2007

24. Ocean acidification: Impacts on individual marine organisms Non-calcifying marine algae: Increased photosynthesis and growth • Lower pH means more dissolved CO2 for photosynthesis to fuel growth • Fitness effect: higher survival and population growth Photosynthesis Growth Amount of dissolved carbon Chen & Durbin 1994

25. The Solutions What can we do about ocean acidification?

26. A possible geoengineering solution: Add CaCO3 to the ocean. Reduce CO32- under-saturation caused by excess CO2 dissolving in ocean water. Shells are made of CaCO3 = Ca2+ + CO32- Shells are made of CaCO3 = Ca2+ + CO32- H+ CO32- From the wikimedia free licensed media file repository Sounds great, but……………..

27. To counteract 2 gigatons of carbon/yr input of CO2, would need 20 gigatons of CaCO3/yr. White Cliffs of Dover would be rapidly consumed. Limestone Rock (CaCO3) • Limestone mining would be expensive and would cause ecological damage. • All the energy needed to move massive amounts of rock into the ocean would likely add more CO2 to the atmosphere.

28. What about Fe fertilization to take care of CO2 already in the atmosphere? Biological Pump Phytoplankton - Forams Fe fertilization – removes CO2 from the atmosphere, but may have decreased effectiveness due to damage to phytoplankton that use calcium carbonate to build shells

29. What about Fe fertilization to take care of CO2 already in the atmosphere? • Foraminifera, commonly referred to as forams, are photosynthetic organisms that live in the surface of the ocean and take up CO2 during photosynthesis. • The CO2 that they take up during photosynthesis becomes part of their biomass and, therefore, they help remove CO2 from the atmosphere. • When they die, they sink to the bottom of the ocean and with them goes the biomass. This overall process helps decrease the amount of CO2 in the atmosphere.

30. What about Fe fertilization to take care of CO2 already in the atmosphere? • However, these organisms will be unable to function properly in more acidic oceans. • However, if plankton using the Fe (such as forams) can’t function properly, then Fe fertilization will not work. • There is incomplete shell growth and malformed shell plates of foraminifera under more acidic conditions. • The chemical composition of the sea urchin spine is 94 percent mineral (calcium carbonate, magnesium carbonate and silica) and 6 percent organic matter.

31. Oh yes, Stop adding CO2 to the atmosphere! From the wikimedia free licensed media file repository

32. The End! Any Questions?