Lab 11.4 – Upwelling and Acidification: A Glimpse into the Ocean’s Future
Fundamental concept: Ocean pH varies with ocean CO₂, which is influenced by both biological and physical processes in upwelling regions.
Estimated time to complete: 20 minutes
Data skills preparation:
Materials needed: None
In Lab 11.3, we learned that seawater with relatively higher concentrations of carbon dioxide, CO₂, will have lower pH values and be more acidic. We also learned that deeper water has higher concentrations of carbon dioxide and therefore lower pH than surface waters. Now, let’s explore seasonal patterns in CO₂ and pH of surface waters off the coast of Oregon from July 2020 to August 2021.
The figures above show three things: 1) the relationship between CO₂ concentrations and ocean pH, 2) trends in ocean pH over time, and 3) trends in ocean CO₂ over time.
Tips (PUT IN WIDGET)
- Select a specific time period to explore that interests you by selecting a range of data in the pH graph (top right). Click to to draw a box over the data points. You can then move the highlighted box to the right or left.
- Zoom in and out of the data to look at different time scales that interest you by changing the width of your highlighted box section in the pH graph (top right).
- The color denotes the time of year the pH data are from (light purple/pink are from the early part of the record, while blue/dark purple are from the later part.
- Orientation Questions
Interpretation Questions
- What is the relationship between ocean CO₂ and ocean pH?
- Give an example of a month with high variability in pH and CO₂?
- Give an example of a month with low variability in pH and CO₂?
- How does the variability in CO₂ and pH change throughout the year?
Now that we’ve explored seasonal patterns in surface CO₂ off the coast of Oregon, let’s look at what physical and biological processes might be driving these patterns.
As we’ve learned, photosynthesis at the ocean’s surface (where there is sufficient sunlight) uses CO₂ and water to produce organic matter and releases O₂ . As a result, CO₂ concentrations are low at the ocean’s surface. At depth, this organic matter is broken down via aerobic respiration. This process – which looks much like the mirror image of photosynthesis – releases CO₂ at depth. Remember that this deep water with high CO₂ would have a low pH. This low pH water depth can be brought to the surface via mixing or upwelling. Upwelling occurs anytime surface water diverges – away from other water, or away from a coastline – allowing cooler, carbon dioxide-rich, low pH water to rise to the surface. Upwelled water is also nutrient-rich and can fuel primary productivity, a topic we explored in Lab 8. Today’s activity is going to focus on upwelling along the coast of Oregon, and specifically on data collected at the Oregon Shelf Surface Mooring.
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.
Coastal Upwelling on West Coast of United States.
Now let’s look at patterns of wind along with carbon dioxide concentrations and pH throughout the same time period you explored in the beginning of this lab activity.
The two bottom plots (pCO₂ and pH) show the same data as the graph that we explored from the Oregon Shelf Surface Mooring at the start of this lab, but we have now included wind direction and speed in the top graph. Think about what you just learned about the impact wind has on upwelling in this region. Compare the wind data to the pCO₂ and pH data, look for relationships, and answer the questions that follow.
Orientation Questions
- What is the date range provided by these data?
- What are the units of wind in this figure?
- For which values (positive or negative) in the top graph is the wind moving towards the north?
Interpretation Questions
- a) What season is associated with mostly northward winds (winds blowing from south to north)? b) Are northward winds associated with more or less variable pCO₂ concentrations? c) How does ocean pH vary throughout this same time period?
- Do the lowest pH values occur when the wind is blowing toward the north or toward the south in this region?
Application Questions
- Based on what you know about upwelling, during what season do you think upwelling is occurring off the coast of Oregon? Briefly explain your answer, making sure to discuss how all three variables in the time series above are linked.
- What do you think would happen to animals that have calcium carbonate shells, when this low pH water is upwelled to the coastal region?
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 near where the data you just analyzed was collected.
As you have now learned, upwelling brings deep water with lower pH to the surface of the ocean. Upwelling regions can therefore serve as a proxy to help us understand the impacts that lowering ocean pH has on marine life. By completing Lab 11 you have discovered that as more CO₂ is released into the atmosphere from the use of fossil fuels, the CO₂ concentrations in ocean surface waters increase which leads to a decrease in the pH, a process known as ocean acidification. By studying upwelling regions, scientists can identify the impacts this lower pH will have on marine life due to ocean acidification.
Reflection Question:
- To summarize your understanding of global change as it particularly relates to ocean acidification: In your own words, describe the impact that anthropogenic activities have on shell building marine animals.
- What can society can do and what can you personally can do to decrease this impact.
