Lab 11.4 – How do biological processes shape CO2?
Fundamental concept: Ocean CO2 is influenced by the biological processes of photosynthesis and respiration/remineralization.
Estimated time to complete: 20 minutes
Data skills preparation:
Materials needed: None
When you hear about CO₂, it’s often in a negative context: an excess of it can lead to more heat being trapped on Earth, contributing to global warming and issues like ocean acidification. However, CO₂ is also essential for photosynthesis—a biological process through which plants use sunlight, nutrients, and carbon dioxide to produce sugars and oxygen – substances that all animals need to survive! Animals (and plants, too!) then break down this glucose through cellular respiration, a process that releases energy for biological functions and returns CO₂ to the atmosphere. The problem arises when we burn fossil fuels—ancient organic matter formed from long-dead plants and animals—releasing large amounts of CO₂ that were previously stored underground, disrupting this natural balance and contributing to climate change.
Before we get into the nitty-gritty of photosynthesis and respiration, let’s watch this video showing temporal and spatial patterns in CO2 throughout the year on earth. While you watch this video, identify any patterns you see, and try to think about what might be causing them. Remember that photosynthesis uses CO2, while respiration and fossil fuel burning creates CO2.
Orientation Questions
Interpretation Questions
- How do concentrations of CO2 vary spatially? Are they higher in the Northern Hemisphere or in the Southern Hemisphere?
- Now focus on the Northern Hemisphere – how do concentrations of CO2 vary seasonally?
Now let’s get a bit more comfortable with the basic photosynthesis equation. Given what we’ve discussed so far, do your best to place the components of this equation in the correct spot.
Photosynthetic plankton consume CO2 in the surface ocean, where sunlight is readily available, which mitigates increased CO2 concentrations in the atmosphere. This process also produces oxygen, helping to keep the planet hospitable for life. Plankton also need nutrients like nitrate (NO3–), phosphate (PO43-), and iron (Fe), to photosynthesize. These nutrients are used up during photosynthesis and are released when organic matter is broken down, similar to CO2. We can add nutrients into a simplified version of the photosynthetic equation you filled out above.
In the deep ocean, away from the sunlight, microbial respiration consumes oxygen and produces CO2. Therefore CO2 will be low at the surface, where it is being used up, and will be high at depth, where the constant rain of organic matter is broken down. NO3– and PO43- will show patterns similar to CO2 with depth.
Quick Check – Can you predict where photosynthesis will occur in the ocean?
Now that we’ve explored the chemical and biological processes linking CO2, pH, O2, and NO3–, we can predict how their vertical profiles would compare. The following widget shows chemical data analyzed on board a research vessel at a long-term study site called Station Papa. Can you predict the vertical patterns of nitrate and pH based on the observed patterns in CO2 and O2?
