ERTH 160L Lab Week 6

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Long Beach City College *

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160L

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Geology

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Dec 6, 2023

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GEOL 160L Name: Lab 7: Ocean Water Chemistry ______________________________________________________________________ PURPOSE Learn how water samples are collected in the deep ocean. Explore ocean stratification and how temperature, salinity, and dissolved oxygen change with depth. INTRODUCTION The chemistry of ocean water can determine how well the surface of the ocean will mix with the deep ocean. As the chemistry of the ocean changes from the surface to the deep ocean, the water can divide into layers. Each layer may have a different chemistry. Chemistry strongly impacts life in the ocean. Animals cannot live where there is no oxygen, and the hard parts of animals will dissolve in the deep ocean below the CCD. Part 1. How we collect ocean water. It takes special equipment to collect water quality data and a water sample from a mile beneath the ocean. At great depths, the water is cold, and the pressure is high—so high it can crush equipment. Part 2. General water quality data Oceanographers routinely measure certain chemical parameters. Some parameters are easy to understand (like temperature). Others are less intuitive (like pH). pH is a controlling factor of the CCD and warrants more exploration. On the powerpoint, there is a link to the Gizmos website that lets us explore the pH of common household solutions. Using the website in your breakout group, measure and record the pH of the following: Fluid pH Coffee 5 Cola 2.5 Milk 6.5 Bleach 11 Drain cleaner 13 Distilled water (like at the store) 7 Ocean water (this is an average!) 8

1. What do you notice about the pH of many of the common things we drink? Knowing about what happens below the CCD, why might some of these beverages be bad for our teeth? Water, one of the most common things we drink, has a perfect neutral pH of 7, so it is safe for teeth and helps rinse away things that may harm teeth. In contrast, a lot of other common drinks, like coffee and especially soda, is highly acidic. Knowing that almost no calcium carbonate is preserved below the CCD due to the higher presence of carbonates as the rate of calcium carbonate accumulation becomes equal to the rate of dissolution, I can assume that similar things are happening in the mouth as we drink acidic beverages; the rate that enamel (which has calcium in it) is growing stronger to protect the teeth is the same as the rate of the dissolution of that enamel. So overtime, the more often you drink acidic drinks, the more the acid has time to destroy the enamel protecting the teeth. 2. What about the pH of common household cleaners? Are they acidic or basic? Basic 3. Why do you think that ocean water is more basic (higher pH) than distilled water? Ocean Water is more basic than distilled water because it has higher salinity and alkalinity. Not only does runoff majorly impact the salinity of the water by eroded rocks containing salt being dissolved in the ocean, but it has a similar effect on alkalinity, as eroded rocks containing carbonate and hydroxide are dissolved in the ocean. 4. Study the graph in slide 13. (Labeled More CO 2 = more acid) a. What is your x axis? Soluble CO2 (mg/l) b. What is your y axis? Water Depth (m) c. What do the different colored lines represent? Different temperature ranges

5. From this graph in question 4, we can learn a number of things that relate the data on the y-axis to the data on the x-axis. a. What is the relationship between depth and the amount of CO 2 that can dissolve in water? (Hint: as one gets bigger, what does the other one do?) As water depth gets deeper (larger), the amount of CO2 that can dissolve in the water gets larger. b. What is the relationship between temperature and the amount of CO 2 that can dissolve in water? As temperature gets lower, the amount of CO2 that can be dissolved in water gets larger. c. Knowing now about these relationships, explain why the deep ocean does not preserve calcite fossils (coccoliths and forams). Going deeper into the ocean causes an increase in pressure, which can lead to the dissolution of calcium carbonates, including calcite. d. Why is it that more CO2 can be stored in deep water? As pressure increases, water becomes denser and colder, and can hold more dissolved CO2 Part 3: Ocean Stratification Oceanographers often study the changes of these different chemical parameters with depth—because they often change! These changes are hugely important as they can explain a lot about ocean currents, ocean acidification that attacks coral reefs, and where certain organisms can live. To appreciate these changes, we need to review: Review and extrapolation of density 6. What is density? (Define it both generally and with the units we use to measure it with) Density is how tightly the molecules of a substance are packed together, or how heavy something is for its size. Density is measured in mass per unit volume 7. a. Where else have we discussed density? We have also discussed density in the context of Earth’s plates and how they move. Convergent plates move towards each other, the denser one slipping underneath the other one. b. Why was it important in that lab (i.e., what did it control)?

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Because it was important to note that similarly to Earth’s tectonic plates, the denser one will sink further down than something less dense. c. Do you think that it is important in the oceans for the same reason? Yes, denser, colder, less inhabitable water with more CO2 sinks below the ocean water that is less dense and warmer, with less CO2 impacting the solubility. 8. What chemical parameters (ex. pH, T, etc) do you think control the density of sea water and why? Chemical parameters that I believe control the density of the sea include: - Temperature: when the temperature of water decreases, molecules are packed closer and occupy a smaller volume, which increases the density (increases the mass per volume unit) - Salinity: deeper ocean water tends to be denser not only because of temperature, but because of salinity. This is largely due to the evaporation and precipitation that occurs on the surface; Areas of the globe where evaporation is high due to high temperatures (low latitudes – Tropics of Capricorn & Cancer) tend to have the highest salinity in the ocean. Near the equator, the evaporation increase is partially counteracted by higher rates of precipitation and therefore runoff, which makes the salinity of the ocean water have less salinity than low latitudes. Areas of the globe with generous precipitation and low rates of evaporation due to lower temperatures (as well as the melting of glaciers) tend to be lowest in salinity Plotting and interpreting your own data. In the excel sheet provided, there is data collected by the CTD on the Nautilus . You will make three graphs (plots). Follow the attached instructions. Plotting in excel is a useful skill for any major and career. In each plot, Depth (m) will be on your y-axis and will increase from top to bottom. On the first plot, you will put Pressure on the x-axis. Copy the plot and paste it in the box above Fig. 1. On the second plot, you will put temperature on the x-axis, copy the plot and past it in the box above Fig. 2. On the thirdd plot, you will put salinity on the x-axis, copy the plot and past it in the box above Fig. 3. *The boxes will change size to fit your graph! Then use the graphs to answer the questions.

Fig. 1. Pressure (PSI) vs Depth (m) 9. What is the relationship between pressure and depth? The relationship between pressure and depth is a positive one, meaning they move in the same direction; as depth increases, so does pressure. Fig. 2. Temperature ( o C) vs Depth (m) 10. Where is the ocean water the warmest? Why do you think that is? The water in the ocean is warmest near the surface, which I think is attributed to the fact that the sun penetrates the surface and is absorbed rapidly with depth,

and also that colder, more saline water is denser and sinks below the surface waters that are interacting with precipitation, evaporation, runoff, etc. 11. What is the overall relationship between temperature and depth? The relationship between temperature and depth is overall a negative one, meaning they move in opposite directions. As depth is increased, the temperature of water is decreased. This occurs slowly but picks up pace and remains steady past a certain depth. 12. Between what two depths is the sharpest change in temperature? Between 200m and 1000m, temperature of the water rapidly declines at a quick rate because this is the zone of the ocean where warm surface water and cold deep ocean waters meet. 13. From class, what is this zone called? The Thermocline Fig. 3. Salinity (PSU) vs Depth (m) 14. What is the depth(s) of the lowest salinity? Why do you suppose that is? 0m (the surface) through 100m have the lowest salinity, which I assume is because of the constant precipitation and evaporation happening to the surface waters. 15. Between what two depths is the sharpest change in salinity? Between 300m and 1000m, salinity begins to increase at a quicker rate that between 0m and 300m, which displays and slow and steady increase.

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16. From lecture (or an earlier slide), what is this zone called? The Halocline 17. If density of sea water increases with salinity and increases with colder temperatures, what can you say about the density change with depth in this part of the ocean? Considering the rapid increases of salinity and colder temperatures that occur within the Halocline and Thermocline, I can infer that density rapidly increases as well. 18. Would you say that the ocean is stably stratified (i.e., hard to mix)? Yes, I would say that ocean stratification is stable because of these defined zones of changing properties in water.

ERTH 160L Lab Week 6

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