7A: C02 And Ocean PH - What's The Connection? - SERC - Carleton

Ocean Acidification

Part A: CO2 and Ocean pH - What's the Connection?

Oyster farmers sound the alarm about ocean acidification

Oyster farmers have been on the front lines of ocean acidification. In Washington and Oregon, oysters farms are in coastal Pacific waters where upwelling currents are bringing up cold, deep water with higher amounts of CO2 and a more acidic pH. Watch and listen to two oyster farmers from Taylor Shellfish Farms in Washington state talk how about ocean acidification is impacting their young oysters.

Discuss

Why is ocean acidification important to oyster farmers?

Surface ocean acidity has increased by 30% since pre-industrial times

× Changes in ocean acidity as measured by pH. Blue indicates less acidity; yellow/orange indicates greater acidity. Source: US National Center for Atmospheric Research Community Climate System Model 3.1 (CC SM3)-modeled decadal pH at the sea surface centered around the years 1875, 1995, 2050 and 2095.Recent estimates by scientists ( Le Quere et al., 2012) have calculated that approximately 26% of all CO2 emitted from human-related activity was absorbed by the oceans during the decade 2002 - 2012. That's 2.5 billion gigatons of excess carbon that moved from the atmosphere into the ocean each year during that one decade. Some of this excess CO2 ends up in deep ocean currents that eventually upwell along coastal areas bringing all that excess CO2with them and to oyster farms.

Scientists have also observed that the oceans have become more acidic since the beginning of the Industrial Revolution. They project that this trend will continue in this century as indicated in the visualization pictured on the right. Scientists are concerned that ocean acidification—a gradual acidification of seawater—could have negative consequences for marine organisms, marine food webs, and entire ecosystems. To better understand what ocean acidification is and why it happens, you will:

• learn about pH chemistry in sea water
• conduct a short experiment to investigate the relationship between increased CO2, acidity and pH
• analyze and compare times series data sets of atmospheric CO2, sea surface CO2 and ocean pH

Understanding pH Chemistry

× pH scale. Click to Enlarge. Image Source: WHOI You have probably used pH paper and a pH scale in past science classes to determine how acidic or basic (alkaline) a substance is. Whether a substance is an acid or a base depends on the concentration of hydrogen (H+) ions an atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons. compared to the concentration of hydroxide (OH-) ions in solution. A pH scale is used to measure the concentration of (H+) ions.

1. Click to enlarge the pH scale image on the right.
2. Take a few minutes to examine the relationship between the pH value (1-14) and the concentration of (H+) ions compared to the concentration of hydroxide (OH-) ions. Also pay attention to the logarithmic scale on the left which illustrates how much the concentration of H+ ions changes relative to the neutral pH of 7. Key points to know about the pH scale and acidity:
   • The lower the pH value, the more acidic the solution.
   • The higher the pH value, the more basic (alkaline) the solution.
3. The pH scale is based on a logarithmic scale (powers of ten). For example, pH 7 is ten times more acidic than pH 8. pH 6 is 100 times (10 X 10) more acidic than pH 8. This means that even a small change in pH can significantly change the concentration of H+ ions in seawater.
4. The term "acidity" does not mean the same thing as a solution being an "acid." For example, if a pH value of a substance changes from pH 10 to pH 9, the concentration of H+ ions increases making the substance more "acidic" but not making the solution an acid. To be an acid, the pH value has to be less than 7. This concept will become important in understanding ocean acidification.
5. NOTE: If you have no prior knowledge of pH, acids and bases, you may want to watch this video: Acids, Bases & pH - bozemanscience

Checking In

Based on your understanding of the pH scale, which of the following statements are TRUE? A neutral pH of 7 indicates that the concentration of (H+) ions is equal to the concentration of (OH-) ions. The lower the pH, the higher the concentration of (OH-) ions compared to the concentration of (H+) ions. The pH of an unknown solution changed from pH 5 to pH 4. This means that the concentration of (H+) ions increased by ten times. The lower the pH, the more acidic the solution. Seawater is an acid. The pH of seawater would become more acidic if the concentration of (H+) ions increased. The pH of seawater since the Industrial Revolution has changed from 8.2 to 8.1. This means the concentration of (H+) ions has decreased.