Posted by: lapazfarm | September 23, 2009

pHun with seawater

Sorry I’ve been so slack about getting pics up here. I have had a bit of a cold and it really took the wind out of my sails. I hardly took any pictures at all last week, so you know I wasn’t feeling well!LOL!

But I did get a shot or two of Superboy doing the water chemistry experiment.

He used some pH strips and determined that the seawater he collected had a pH of approximately 8, so a bit basic….

He blew air through the water until he nearly passed out…

Just kidding. He has lungs of steel, this boy.

After all that blowing he re-tested the pH. Here he has achieved a pH of 7:

A bit more blowing and he was able to lower the pH to a respectable 6 or so.

So. Why does blowing air through water lower the pH, you ask?

It’s simple. The air you breath out is rich in CO2 (carbon dioxide). When CO2 is mixed with water, some of it dissolves into the water, forming carbonic acid. This is the same acid that is in sodas (“carbonated beverages”).

So. Why is this important? A couple of reasons:

1. Just like plants on land, phytoplankton need CO2 for photosynthesis. They absorb it directly from the CO2 dissolved in the ocean water. The CO2 in the ocean comes from the atmosphere. So, phytoplankton, the base of the ocean food chain, is dependent upon the ability of ocean water to absorb CO2 from the atmosphere.

2. The ocean is a great big carbon sink and so very important to global carbon balance. As CO2 levels in the atmosphere rise, much of  it is absorbed by the ocean. But no one really knows the limit of the ocean’s ability to absorb excess CO2. Plus, no one really knows the effects will be on the ocean for absorbing all that excess CO2. Possibilities include an increase in  acidification of the oceans (not good), increased algae blooms (also not good). On top of that, as CO2 levels rise and the atmosphere warms (CO2 being a major greenhouse gas), the ocean warms too. And warm water cannot absorb as much gas as cool water can. So we get a sort of snowball effect of more atmospheric CO2 but less absorption.

It’s all very complicated. Who knows where it all will lead, but all this underscores the need for us to understand the interaction between the ocean and the atmosphere.



  1. Great job SB!! I having a dickens of a time finding the pH strips, where did you acquire yours???

    • Hmm…good question. We’ve had them forever. You might try a pet store with the aquarium supplies or a garden center with a soil test kit. Oh! Another thought…don’t swimming pool supply places have them also for testing pool water? You might want to call around and perhaps some educational, teacher-ish supply stores may have them as well.

  2. Hi Meredith,
    Just an f.y.i. I found my ph strips in a Health food store.

    • Great, I’ll try all of the suggestions, one of those options should work eh? Thanks everyone 🙂

  3. Here’s a link to the post on of our latest work:


  4. Hey,

    We are beginning Porifera this week which also includes sea geography. I have a word document resource you may want to consider posting. It is a resource from the geology department at the College of Charleston. JV is going to make a pin map of the information found it it. Let me know if you want to look at it.


    • Yes! send it on!

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