Lab 11.3 – How do physical processes shape CO2?
Fundamental concept: The ocean exchanges CO2 with the atmosphere and can act as a sink or source for this greenhouse gas.
Estimated time to complete: 15 minutes
Data skills preparation:
Materials needed: None
As discussed in Lab 11.1, the ocean and the atmosphere are intimately linked and are constantly exchanging gasses like O2 and CO2. In this activity, we are going to dive a bit deeper into these interactions, and discuss when the ocean is a sink versus a source of CO2. The ocean is said to be a sink for CO2 when the net movement of CO2 is from the atmosphere to the ocean, or when the ocean is taking up CO2 from the atmosphere on average. The ocean is a source of CO2 when the net movement of CO2 is from the ocean to the atmosphere, or when the ocean is releasing CO2 to the atmosphere.
Ocean Carbon Uptake by NOAA is licensed under the Public Domain. Original Source.
The figure above helps to summarize these interactions within the ocean carbon uptake system. We will learn more about the role of biological processes in later activities. For now, let’s focus on gas exchange and on the solubility cycle. Solubility refers to the amount of dissolved gas that the water can hold under a particular set of conditions, which are usually defined as 0℃ and 1 atmosphere of pressure. The solubility of a gas increases with increasing pressure, decreased temperature, and decreased salinity.
Solubility by OpenStax is licensed CC BY 4.0. Original source
Use the above figure showing the solubility of several gases in water and its relationship with temperature to answer the questions below.
Orientation Questions
- How many different gasses are shown in the figure? Is CO2 one of these gasses?
Interpretation Questions
- Briefly describe the relationship between the solubility of oxygen and the temperature of water.
- Is this relationship the same across all gasses? Choose one other gas to compare/contrast with oxygen in terms of this relationship.
Saturation refers to the amount of gas currently dissolved in the water, relative to the maximum possible content of that gas. If the water is undersaturated, more gas can dissolve. If the water is saturated or supersaturated, gas may be released. Therefore, when the ocean is undersaturated with CO2 it can act as a sink and. When it is supersaturated with CO2, it can act as a source.
The figure above shows three different time series relating to CO2. The top panel shows CO2 concentrations in the atmosphere (in gold) and CO2 concentrations in seawater (blue). The bottom panel shows how much CO2 is being transferred from the ocean to the atmosphere – also called the “flux” of CO2 from the ocean to the atmosphere. During the time period shown, atmospheric CO2 was approximately 405 ppm.
An Aside on Units: MAKE A TOGGLE Show more, show less
- ppm – Refers to “parts per million” (i.e., as opposed to “parts per hundred”, which would be percent!) and is a way that the amount of CO2 in seawater or atmosphere is measured. It is a measure of the concentration of a substance. The amount of CO2 may also be reported in another measure of concentration, µatm, or microatmospheres.
- mol m-2 s-1 – Can be read as “the amount of substance (measured in moles) that is transferred or produced over an area of one square meter per second”. Unlike ppm, which is a measure of concentration, this is a measure of flux or movement – of how much gas is being exchanged between the ocean and atmosphere, in this case.
Orientation Questions
- What time period is displayed in the graph?
- What is the range of values seen in the air pCO2 values on the Oregon Shelf?
- What is the range of values seen in the ocean pCO2 values on the Oregon Shelf? Are these values more or less variable than those seen for the air?
Interpretation Questions
- When is the ocean a source for CO2 during the time period shown? When is it a sink?
