Lab 11.6 –  When the Ocean Breathes: Uncovering the Drivers of CO₂ Seasonality

Fundamental concept: Seasonality in upwelling, driven by seasonality in wind direction, drives variation in ocean surface CO2.
Estimated time to complete: 30 minutes
Data skills preparation:
Materials needed: None

Now that we’ve explored seasonal patterns in CO2 off the coast of Oregon, let’s look at what physical and biological processes might be driving these patterns. In this region, the Coriolis effect interacts with wind to lead to seasonal cycles of upwelling. As a reminder, the Coriolis effect leads to a net movement of 90° to the right of the driving force (in this case, the wind) in the Northern Hemisphere. The image below shows what is happening in this region when the wind patterns are favorable for upwelling. 

Drawing showing a coastline on the west coast of the U.S. with wind blowing at of the north causing coastal upwelling

Drivers of hypoxia and acidification in upwelling shelf systems by Mikhail Ryazanov is licensed under CC-BY-SA 4.0.

 

Now let’s look at patterns of wind and chlorophyll throughout the same time period you explored in Activity 5. We are going to explore these data in two different ways.

First, let’s look at a spatial representation of how chlorophyll and wind patterns vary between the northern hemisphere winter (January 2021) and summer (July 2021) in this region. The benefit of these spatial data is that they allow you to look at how variables vary across space, but the downfall is that they only provide information on a snapshot in time.

Map of the coast of Oregon showing wind direction and chlorophyll concentration in January and July of 2021

Orientation Questions

 

Interpretation Question

  1. What is the general wind direction along the coast in January 2021? How does this compare to June 2021?
  2. When are there higher rates of photosynthesis along the coast, in January 2021 or in June 2021?
  3. Approximately how much higher are chlorophyll concentrations during the month you chose in the previous question?

Now, let’s look at similar data from the same region, but let’s look at them over time. These time series data are a nice complement to the spatial data we examined above because they provide information from a single location but allow us to look at these data at more than one date. The two bottom plots (pCO2 and pH) show the same data as the original widget that we explored from the Oregon Shelf Surface Mooring.

Four graphs are displayed showing chlorophyll, northward wind, pCO2 and pH off the Oregon shelf from July 2020 to July 2021

Orientation Questions

  1. What is the date range provided by these data? How does this date range compare to the spatial data we explored above?
  2. What are the units for chlorophyll a in this figure?
  3. What range of chlorophyll a values is shown over this time period?
  4. What are the units of wind in this figure?
  5. For which values in this figure is the wind moving towards the north?

Interpretation Question

  1. What seasonal patterns in chlorophyll are shown in the figure? Do these seasonal patterns align with the spatial data figure you explored above?
  2. What seasonal patterns in wind are shown in the figure? Do these seasonal patterns align with the spatial data figure you explored above?
  3. Are northward winds associated with higher or lower chlorophyll concentrations?
  4. How do relationships in ocean CO2 and in ocean pH vary throughout this same time period?

Application Question

  1. Based on what you know about upwelling, when do you think upwelling is occurring off the coast of Oregon? Briefly explain your answer, making sure to discuss how all four variables in the time series above are linked.

HINT WILL TOGGLE OPENED AND CLOSED

Hint: Upwelling can have two impacts on ocean surface CO2 levels:

  • An increase in CO2 levels when deep ocean water is brought to the surface. Remember that higher pressure = higher gas concentrations. Deep ocean CO2 levels are also higher due to a lack of photosynthesis and the breaking down of sinking organic matter through respiration.
  • A decrease in CO2 levels due to an influx of deep-water nutrients and, as a result, higher rates of photosynthesis.

Bringing it Full Circle: Survival of Oyster Larvae on the West Coast

We started this chapter by discussing how a reduction in ocean pH can influence oysters on the East Coast of the United States. Now, let’s put these threats in the context of the West Coast, at a shellfish hatchery near the Oregon Shelf Surface Mooring. 

 

 

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