Lab 11.2 – Sky to Sea: Unraveling the Carbon Connection
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: time series
Materials needed: None
As discussed at the end of Lab 11.1, the ocean and the atmosphere are intimately linked and are constantly exchanging gases like O₂ and CO₂. In this activity, we are going to dive a bit deeper into these interactions and discuss how we can tell 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 (when the ocean serves as a net absorber of atmospheric CO₂). The ocean is a source of CO₂ when the net movement of CO₂ is from the ocean to the atmosphere (when the ocean is releasing CO₂ to the atmosphere).
Modified from: 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 about the role of biological processes and upwelling in later activities (Lab 11.3 and 11.4, respectively). For now, let’s focus on gas exchange between the atmosphere and ocean.
The following figure shows three different time series relating to CO₂.
The top panel shows CO₂ concentrations in the atmosphere (in gold) and CO₂ concentrations in seawater (in blue). The principle of diffusion states that substances move from areas of higher concentration to areas of lower concentration. If CO₂ concentrations in seawater are higher than CO₂ concentrations in the atmosphere, there will be a net movement of CO₂ out of the ocean and into the atmosphere; under those conditions the ocean is a source of CO₂.
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. Positive flux values indicate that CO₂ is moving from the ocean to the atmosphere and that the ocean is a source of CO₂. Negative flux values indicate the opposite: that CO₂ is moving from the atmosphere into the ocean and that the ocean is a sink for CO₂. Negative flux occurs when CO₂ concentrations in seawater are lower than CO₂ concentrations in the atmosphere. During the time period shown, atmospheric CO₂ was approximately 405 ppm. First review your understanding of flux and the movement of CO₂, then analyze the graphs below and answer the questions that follow.
Quick Check Questions
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 Question:
- Describe the patterns in CO₂ flux that you see throughout the year at the Oregon Shelf Surface Mooring. Is there any clear seasonality in these patterns?
- Now switch to look at the Pioneer NES Inshore Surface Mooring by clicking on this option below the graph. This station is located off the east coast of the U.S. in the Atlantic Ocean. Is the temporal pattern seen here the same as that off the coast of Oregon?
Reflection Question:
- When averaged throughout the year at the Pioneer NES Inshore Surface Mooring, is the net movement of CO₂ (1) from the atmosphere to the ocean or (2) from the ocean to the atmosphere?
- Remember that anthropogenic atmospheric CO₂ is a greenhouse gas and traps heat near the earth’s surface. Based on your answer to question #6, how does the ocean impact global temperature?
