Study Guide

Environmental Chemistry Themes

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  • Biology Meets Chemistry

    We know that the ocean is a carbon sink and that the burning of fossil fuels is increasing the concentration of carbon dioxide in the atmosphere. Up to 50% of this excess CO2 is absorbed in the ocean. When CO2 dissolves in water, it forms a weak acid known as carbonic acid:

    Reaction 6.4: CO2 (aq) + 2H2O → HCO3-(aq) + H3O+ (aq)

    The increase in H+ ions released from carbonic acid shifts the reaction toward bicarbonate (HCO3-), and away from carbonate (H3O+). The end result is that less calcium carbonate is available to marine organisms.

    This formation of carbonic acid can be illustrated using some cabbage juice indicator, straws, and various water samples. Add cabbage juice to each cup of water to record the starting pH. Then, using the straw, blow bubbles in each cup of water for 30-60 seconds. The color should change, indicating a change in pH. Unless you exhale different gases than everyone else, the pH will decrease. How much it decreases depends on the starting pH and the alkalinity of the water.

    On a much larger scale, this is what is occurring in the ocean. This process is known as ocean acidification. The current pH of the ocean hovers around 8.1, but the projected pH for the end of the century is 7.7. This drop in pH will directly affect calcifiers, organisms that use calcium carbonate to build their shells. Examples of calcifiers include marine snails, crabs, sea urchins, lobsters, and coral. As pH levels plummet, the amount of calcium carbonate available to organism also plummets.

    Some types of calcifiers use aragonite to build their shells. The diagram below shows the change in aragonite saturation in the oceans from 1880 to 2012. In areas with large decreases in aragonite saturation (indicated in red and orange), calcifiers that depend on aragonite will likely decrease their calcification rates. The effects could range from thinner shells and skeletons, to the complete dissolution of shells. Of course, other factors like rising temperatures also affect calcification rates. (Source)

    It is likely that different types of calcifiers will respond differently to ocean acidification. In experiments, crabs and lobsters have built heavier thicker shells when exposed to lower pH levels. Sea urchins and pteropods tend to build thinner shells as pH levels plummet.(Source)

    In addition to affecting calcification rates, increasing levels of carbon dioxide also affect reproductive success by either slowing down sperm or causing problems in larval development. There have been recent reports of urchins that have already adapted to lower pH levels. Genes controlling ion transport in purple sea urchins exposed to lower pH levels show more changes than those same genes in purple sea urchins not exposed to lower pH levels27.

    New research indicates that purple sea urchins might be able to keep up with ocean acidification. Urchins exposed in the lab to lower pH levels seemed to be able to evolve quickly by mutations in genes controlling ion movement into and out of the cell. Scientists think the sea urchin's unusual degree of genetic variability might be what allows for this rapid evolution. (Source)

    Photosynthetic organisms, like algae and seagrass, might benefit from increasing levels of carbon dioxide in the ocean. From biology, we know that carbon dioxide is a reactant in photosynthesis. More carbon dioxide, then, means greater rates of photosynthesis. This is good news for photosynthesizers and anything that consumes them.

  • Physics Meets Chemistry

    The Auroras: A Light Show

    We've all seen the pictures of auroras, and we probably have all asked ourselves, "How is that possible? What is that?!" Maybe these questions were followed by a moment of sheer panic, or the desire to eat some cheese. In any case, this section will answer those burning questions.

    The more common name for the Aurora Borealis is the Northern Lights. The Aurora Australis is the term for the auroras that occur in the Southern Hemisphere. At its simplest, an aurora is the result of charged particles that the sun releases into space. When these charged particles plummet into the earth's magnetic field, they are deflected to the poles where they then crash into gas molecules, causing those fantastic colors.

    Just like the earth, the sun has an atmosphere and a magnetic field. The hydrogen atoms on the sun are exposed to such high temperatures that their protons and electrons essentially boil away and flow out to space at very high speeds. These, combined with the sun's magnetic field, create what is known as solar wind. Like a galactic bully, solar wind forces earth's magnetic field to change its shape. The magnetic field facing the sun is compressed, while the opposite end is stretched into a long tail called a magnetotail.

    An artist's rendering of Earth's magnetic field. The side of the field facing the sun has been bullied into a compressed shape. The magnetotail is the portion that looks like streamers, or alien appendages. The magnetotail is several times longer than the radius of the earth. (Source)

    Being a galactic bully requires an input of energy, and this malevolent energy is stored in the magnetosphere. Eventually, the energy builds up enough, and the stars align just so (metaphorically, not literally) and a voltage passes between Earth's magnetic poles. This voltage shoots electrons toward the poles, where they ascend in the atmosphere until reach the ionosphere.

    Unsurprisingly, the ionosphere is filled with (drumroll please)…ions. Ions have a charge. When the charged particles from the sun (mostly electrons) collide with these ions, the ions release light and electrons. Remember, light is given off when atoms fall from one energy level to the next. The color of the light depends on the element involved. Oxygen causes the green-yellow and the deep red colors in auroras. Nitrogen ions produce blue auroras, while nitrogen molecules produce purple-red auroras.

    The auroras occur around both poles, in bands centered at each magnetic pole. The band can be between 10 and 1,000 km wide and stray as far as 3,000 km from the magnetic pole. Prime spots for viewing these awesome light shows include Fairbanks, Alaska, Northern Canada, and northern Russia. During intense geomagnetic storms, the auroras can even be spotted as far from the poles as Mexico.

    The Aurora Borealis in the North Pole. (Source)

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