Ocean Acidification - PowerPoint Presentation

Ocean Acidification The Fundamental Chemistry Behind This Phenomenon

Objectives Learning Goals Understand how atmospheric CO 2 affects seawater pH Explain the seawater carbonate chemistry reaction(s) Identify acids and bases and how to use universal indicators Misconceptions CO 2 stays in the atmosphere Atmosphere and seawater are disconnected Seawater is becoming an acid, rather than becoming more acidic

Where does it all begin? It begins with the global carbon cycle is the exchange of carbon  between its four main reservoirs—the atmosphere, terrestrial biosphere, oceans, and sediments. https://courses.lumenlearning.com/microbiology/chapter/biogeochemical-cycles/

Anthropogenic Sources of CO2 Key points: Anthropogenic means environmental pollutants originating from human activity Human activity far outweighs natural sources of CO 2 Fossils fuel burning (oil, coal, gas) releases majority of anthropogenic CO 2 Industrial Revolution

How do we know CO2 is increasing? The Mauna Loa Observatory on the island of Hawaii has been recording atmospheric CO 2 and the Station aloha in the Pacifica Ocean has been measuring pCO2 and pH of the seawater. The graph trend show increasing atmospheric CO 2 , increasing pCO 2 in the seawater , and decreasing seawater pH.

Why should we care about ocean acidification? As the ocean continues to become more acidic the delicate balance of the marine ecosystem will be impacted. Reduced calcification rates of shelled organism Increased marco algae growth will change the balance of coral reefs

CO2 Mixes with seawater and dissolves CO 2 CO 2 CO 2 + H 2 O ⇋  H 2 CO 3 ⇋ HCO 3 - + H + ⇋ CO 3 2- + 2H + CO 2 CO2 ~25% of CO 2 released from the burning of fossil fuels is dissolved into the oceans After CO2 dissolves into water, it reacts with water to from the chemical species H2CO3 , HCO3 and CO32- One significant ion that is formed is H + which is responsible for acidification of seawater

How acidic are the oceans? The oceans are not, in fact, acidic, but slightly basic. Acidity is measured using the pH scale, where 7.0 is defined as neutral, with higher levels called "basic" and lower levels called "acidic". Historical global mean seawater values are approximately 8.16 on this scale, making them slightly basic. However, even a small change in pH may lead to large changes in ocean chemistry and ecosystem functioning. Over the past 300 million years, global mean ocean pH values have probably never been more than 0.6 units lower than today (6). Ocean ecosystems have thus evolved over time in a very stable pH environment, and it is unknown if they can adapt to such large and rapid changes. Figure reproduced from the Pew Charitable Trust Policy Brief "Carbon Dioxide and Our Ocean Legacy", by Feely, Sabine, and Fa

Marine Shells and Coral Skeletons Organisms such as corals, clams, oysters, and some plankton are expected to be impacted the most with Ocean Acidification. Coral skeletons and seashells are made from calcium carbonate. Acid reacts with calcium carbonate by dissolving the building blocks that make calcium carbonate. Ca 2+   + CO 3 2-  ⇋   CaCO 3 Increasing CO 2 Decreasing shell size and holes in shells

How does OA affect coral and seashell growth? By looking at the relationship between 2 fundamental chemical equations, we can understand this phenomenon. Carbon Dioxide Mixing with water Equation 1: CO 2 (aq) + H 2 O ⇋  H 2 CO 3 ⇋ HCO 3 - + H +  ⇋ CO 3 2- + 2H + This shows that as CO 2 is added to the seawater, more H + are formed, lowering pH. Calcification of coral skeleton and seashells Equation 2: Ca 2+  + CO 32-  ⇋  CaCO 3 This shows that 2 ions, calcium and carbonate, are the building blocks for forming coral skeletons and seashells. As ocean pH lowers, so does the concentration of CO32- , a major building block for calcification.