A Neutral View of Oceanic pH

Guest Post by Willis Eschenbach

Following up on my previous investigations into the oceanic pH dataset, I’ve taken a deeper look at what the 2.5 million pH data points from the oceanographic data can tell us. Let me start with an overview of oceanic pH (the measure of alkalinity/acidity, with neutral being a pH of 7.0). Many people think that the ocean has only one pH  everywhere. Other people think that the oceanic pH is different in different places, but is constant over time. Neither view is correct.

First, here is a view of a transect of the north Pacific ocean from Alaska to Hawaii, with Hawaii on the top left, Alaska on the top right, and depths shown vertically. ocean ph along transect

Figure 1. Variation in pH by latitude and depth. The graphic is taken from a previous post of mine regarding oceanic pH.

Note that in Hawaii, the surface pH is above 8.05, and in Alaska the surface pH is below 7.7 … and despite that, the marine environment in Alaska is much, much richer in life than the Hawaiian marine environment. This underscores a simple fact—alkalinity is hard on living creatures, much harder than acidity. For example, if you want to dissolve the victim of your latest murder spree, you’d use lye (a strong alkali) and not sulfuric acid (a strong acid). [Well, maybe not you, but your neighbor about whom everyone always said “He always seemed like such a nice man …]

Now, neutral on the pH scale is 7. In line with our bodies’ poor tolerance of alkalinity I just mentioned, we often eat things like lemon juice, which has a pH of around two, which is neutral minus five pH units … whereas the most alkaline foods that we can tolerate have a pH of around eight, which is only one pH unit above neutral.

That’s why fish often have a slimy kind of mucus that covers their entire bodies … to keep from slowly dissolving in the slightly alkaline ocean. And it’s also why a slight trend towards neutrality in the ocean is not worrisome in the slightest.

Having seen the spatial changes in pH from Hawaii to Alaska, Figure 2 shows the temporal changes in oceanic pH in a variety of other marine environments.

Figure 2. pH in different marine environments. DATA SOURCE: PLOS

Figure 2 shows not only the mean pH in these environments, it shows the variation in each environment over time. Note that while the open ocean shows a narrow pH range, a number of marine environments show a wide range over time. Coral reefs and kelp forests, for example, show a large variation in pH, which can be as large as a full pH unit in a single month. To quote from the underlying source for Figure 2:

These observations reveal a continuum of month-long pH variability with standard deviations from 0.004 to 0.277 and ranges spanning 0.024 to 1.430 pH units. The nature of the observed variability was also highly site-dependent, with characteristic diel, semi-diurnal, and stochastic patterns of varying amplitudes. These biome-specific pH signatures disclose current levels of exposure to both high and low dissolved CO2, often demonstrating that resident organisms are already experiencing pH regimes that are not predicted until 2100.

So we’re already experiencing what is supposed to terrify us, the so-called “acidification” of the ocean that is predicted for the year 2100.

For a real-world view of what that difference in variation means over time, Figure 3 shows the data from the Hawaii Ocean Timeseries (HOT) project, and the data from the Monterey Bay coastline.

Figure 3. Surface pH measurements from HOT open ocean and Monterey Bay upwelling coastline. The Hawaii data shows both measured pH (black) and pH calculated from other measurements, e.g. dissolved inorganic carbon (DIC), total alkalinity, and salinity.

As you can see, it’s nothing for any one of the thousands of different species living offshore from me to go through a large rapid swing in pH. It doesn’t seem to bother them in the slightest, they’ve been doing it for millions of years. Not only that, but as you can see from the Hawaii data, the slow drop in alkalinity is gradually moving the ocean towards a more neutral condition, which living organisms don’t seem to mind.

All of which is why I say that the gradual neutralization of the ocean from increasing CO2 is meaningless. It’s also why I say that calling the process “acidification” is merely an attempt to increase alarm. What’s happening is gradual neutralization, at a rate of something like 0.018 ± .001 pH units per decade (mean of seven multidecadal pH datasets) … color me unimpressed.

So with that as prologue, let’s take a look at the oceanographic pH data which I discussed in my recent post called pH Sampling Density.  In that post I noted that there should be enough data in either the area around Japan or in the North Atlantic to form some idea about the usability of the dataset. To begin with, here is the Atlantic data, along with Hawaiian HOT data and the Monterrey Bay data.

Figure 4. Atlantic pH measurements from oceanographic transects (blue circles), Hawaiian single-location HOT pH measurements (red-calculated, black-observed), and Monterey Bay pH measurements (cyan, with the standard deviations shown by whiskers). Black line is the expected decline in oceanic pH due to the increase in CO2. “Trend 1970 onwards” is the trend of the Atlantic oceanographic pH data.

There are several interesting aspects of this. First, the decline in the HOT measurements is close to the calculated decline due to CO2. Now, I have estimated this decline using the measured average changes in dissolved inorganic carbon DIC due to the increased atmospheric CO2. To do this, I’ve used the R code located here.

And while this is only an estimate, it turns out that it’s quite close to both the decline in the HOT and other multi-decadal single-location measurements cited above, and is also matched quite well by the trend in the Atlantic post-1970 oceanographic measurements of -0.019. It’s also worth noting that prior to about 1960 the calculated decline in pH is so small as to be almost invisible.

Next, Japan. This area has quite a bit more data, but like the Atlantic, unfortunately there is little data from about 1940 to 1960. Figure 5 shows the Japan data in the same format as Figure 4.

Figure 5. pH measurements from oceanographic transects off of Japan, (blue circles), Hawaiian single-location HOT pH measurements (red-calculated, black-observed), and Monterey Bay pH measurements (cyan, with the standard deviations shown by whiskers). Black line is the expected decline in oceanic pH due to the increase in CO2. “Trend 1970 onwards” is the trend of the Japanese oceanographic pH data.

Once again we see the same pattern as we saw in the Atlantic data, with an increasing trend in the latter years of the data, and a post 1970 trend of the same order of magnitude as the average of the seven multi-decadal studies cited above.

So there you have it. The oceanographic dataset confirms the gradual decline in pH, but doesn’t provide enough data prior to about 1960 to tell us much of anything. As usual, the problem is that the changes due to CO2 are so small that they are difficult to dig out of anything but the most accurate of datasets. This doesn’t mean that we can’t use the existing oceanographic measurements … it just means that we need to be cautious in their use.

Regards to everyone,

w.

AS USUAL: If you disagree with someone, please QUOTE THE EXACT WORDS THAT YOU OBJECT TO. Even with threading, it’s often quite difficult to determine what someone’s objection might be. Quoting their own words makes it clear just where your disagreement lies.