The Carbon Cycle and the ‘Acidification’ of the Ocean (Part 3)

The purpose of the previous two articles was to explain the scale of the human contribution to the carbon cycle and to point out that there is significant natural variation as well in the carbon cycle.  The natural variation takes place year to year (ENSO cycle) and over the course of the year (Northern Hemisphere growing season).  All of these variations make it impossible to know precisely how much natural carbon exits and enters the atmosphere naturally each year.  What is known most accurately is how much carbon mankind is putting into the atmosphere.

The Inconvenient Skeptic

Overview of the yearly carbon cycle.

When it comes to the ocean carbon cycle, the certainty is much lower than it is for the atmosphere.  The one thing that is known is that there is far more carbon in the ocean than there is in the atmosphere.  In addition the carbon is not simply absorbed carbon dioxide gas, but it is part of a much more complex balance.  Please note that complex does not mean sensitive or unstable.  It just means it isn’t as simple as CO2 is in the atmosphere.

Most people know that the pH of pure water should be 7.0, but it rarely stays the level for very long if the water is very pure.  That is because CO2 will cause the most basic reaction with pure water to form carbonic acid.

H2O + CO2 = H2CO3

This reaction will quickly lower the pH of pure water to about 5.  This is the idea behind the concept that higher CO2 will cause the oceans to become acidic.  However, it is very easy to prevent this weak acid from forming simply by adding potassium chloride to the water will prevent the acid from forming without shifting the pH of the water.  Guess what the ocean is full of?  Potassium chloride and about every other form of salt known to mankind.

It is also important to remember that the pH scale is a log scale.  Here is the full pH scale with an idea of how acidic or basic different things are.

The ocean pH is not constant either.  Like most things on Earth it is variable by position and time.  The range of the ocean pH is from ~7.90 to 8.20.  The most commonly usage map of the ocean’s pH is the following one.  Ironically enough it gets used to promote fear about acidification, but it is also used to disprove the entire notion of acidification at the same time.

The Inconvenient Skeptic

pH of the Earth's oceans.

Take a careful look at this picture for a moment if you will.  The lowest pH by far is in the tropical regions where the pH is as low as 7.9 which makes it is the most acidic part of the Earth’s ocean.  The highest pH is in the North Atlantic where the oceans are the least acidic (most basic).  Interestingly enough, the regions with the most acidic oceans are also the places where the carbon in the water is lowest.

In fact, there is no correlation with carbon in the oceans and the pH level of the ocean, at least at the ocean’s surface.  The deep oceans are where the vast majority of the Earth’s carbon is stored.  There is already more carbon stored in the deep oceans than there is fossil fuel on the Earth to dig up and burn, by almost 4x.  It is that deep ocean water that has a pH that is slightly below 8.  It is places where that deep ocean water with a low pH rises to the surface that causes the surface pH to drop below 8.

Unfortunately I could not find a well sourced map of the amount of carbon in the ocean, so I had to refer to one on Wikipedia.  However this does appear to be directionally correct.

The Inconvenient Skeptic

Amount of carbon in the the Earth's oceans

This fits accurately with the science that colder water absorbs more CO2 than warm water.  The locations with the highest amount of carbon in general have the highest pH and vice versa.  The theory that high CO2 will cause the oceans to go acidic is not supported by the most basic data of the Earth’s oceans.

Ocean upwelling plays a far more significant role in low ocean pH than anything we are capable of doing.  So let’s look at the numbers.  The most ambitious numbers estimate that mankind is putting about 2 Gt of carbon into the oceans each year.  The ocean surface is estimated to have ~1,000 Gt of carbon, but the deep oceans have 37,000 Gt of carbon.  When those deep ocean currents rise up, they lower the pH of the ocean and bring some of that 37,000 Gt of carbon to the surface.  It is exactly those oceans currents that are the most productive places for life in the oceans.

In total, the oceans have 38,000 Gt of carbon.  At most, mankind is transferring 2 Gt from fossil fuels to the oceans.  That means were are changing the amount of carbon in the oceans by 0.0053% per year.  Yet despite the absurdity that this is going to make a difference, it is the oceans with the least carbon that have the lowest pH.

The idea that slightly higher CO2 levels in the atmosphere will drastically change the ocean pH is just a theory and a bad one at that.  It is one of those ideas makes a certain amount of theoretical sense, but once it is looked at carefully, it simply falls apart.  There is no evidence that the increased atmospheric CO2 will acidify the oceans.  There is also no evidence that the lower pH water caused by ocean upwelling is harmful to sea life.  There is certainly no evidence that sea life cannot survive in water that has 38,020 Gt of carbon instead of 38,000 Gt of carbon.

Every time a whale dives from the surface to a depth of 1,000 meters it experiences a wide range of temperature and pH.  Most mobile sea life deals with that an a regular basis.  There are coral reefs that live at depths of thousands of meters, which means they live fine at the naturally low pH that exists at the depths.  If you want to ignore the science, that is your choice, but the numbers and the science say that ocean acidification is a silly idea.

Posted in Fear and Misinformation and Science Articles - Global Warming and Science Overviews by inconvenientskeptic on March 20th, 2012 at 9:24 am.


This post has 4 comments

  1. John,

    Thanks for the series on ocean pH – I have read them a couple of times now and learn more each time.

    I wonder what happened to Honeycut et al…they seem to have lost interest.

  2. inconvenientskeptic Mar 29th 2012


    It is precisely for that reason that I did my own study of global warming. The summary of my findings are in the book.

  3. inconvenientskeptic Mar 29th 2012


    You ask a good question. I don’t know where they went. I am glad you found this informative. :-)

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