Sagredo : "Ocean acidification - the observed trend in decrease of ocean pH - has been addressed to be the consequence of excess of carbon dioxide in the atmosphere.
This is hard to see, obvious : its effects are happening underwater..."
Salviati : "It has been estimated that at least one-quarter of CO
2 released by combustion of fossil fuels dissolves into the ocean with an impressive rate: something like 22 million tons per day."

Sagredo : "Facing the greenhouse effects as a direct consequence on a higher CO2 world, oceans help to mitigate the process..."
Salviati : "This immediately bounced to the attention of researchers like it has been hiding the evidences under the carpet. And now, tackling the inertia of this phenomena is a bit like trying to close the stable door when the horse has bolted."


Sagredo : "Since the beginning of Industrial Revolution (the automation of production processes on a large scale to increase profits) pH has been estimated to have decreased by 0.1 units (it's a logarithmic scale!). How much is that, ordinary speaking?
Salviati : "Indeed. This means a 30% increase in hydrogen ions concentration from uptake of CO2 from ocean surface. It's a huge price to pay if you consider that the ocean is experiencing a change in pH faster than any known change in ocean chemistry for million years. CO2 immediately becomes carbonic acid dissolving into seawater and the chemistry balance eventually favors the bicarbonate ions, reducing the amount of available carbonate ions. The hydrogen ion concentration will increase proportionally to the ratio between the concentrations of bicarbonate and carbonate ions."

Sagredo : "Will marine life learn to cope with this?"
Salviati : "
Studies have shown that lower environmental calcium carbonate saturation states , basically the availability of calcium carbonate, can have a dramatic effect on some calcifying species at the very bottom of food chain . Some organisms will adapt, survive or even thrive under the more acidic conditions, while others will struggle to, and may even go extinct. We can't predict in any detail how things will look. What we do know is that things are going to look different.

Sagredo : "Aren't rivers carrying enough dissolved chemicals from rocks to the ocean to keep the ocean’s pH stable?"
Salviati :
"Kind of misconception. A long the coast, ocean chemistry is more complicated, more interesting I would say, not just because of your...how do you call it again?..."

Sagredo : "Fishfarms..."
Salviati : "That. I'm really astonished the way you manage to fool all that fish in one place. You see, so much carbon dioxide is dissolving into the ocean so quickly that this natural buffering, that is the property of ocean water to mitigate the effect of dissolution of CO2, hasn’t been able to withstand, resulting in relatively rapidly dropping pH in surface waters. Eventually, as those surface layers gradually mix into deep water, the entire ocean is affected."

Sagredo : "Easy for you to say. We have 7 billions of people on the shore, a great part of them depend on marine life..."
Salviati : "Those that really depend on marine life learnt how to protect it and built a sustainable environment out of it. We are talking of local communities that now are struggling against mass production or just gave up and now are serving the masters in order to survive. On the other side, those rising profits overuse the word sustainability for staying in the market."

Sagredo : "I'm here to ask suggestions, not for being indoctrinated on your ethics...what should we do?"
Salviati : "Measuring".

Sagredo : "Measure what? How sea life respond to ocean acidification?"
Salviati : "Hydrogen ions concentration."

Sagredo : "Using an electrode?"
Salviati : "That's the way it has been since the concept of Sørensen in 1909. Hydrogen-ion activity in water based solution is measured by the difference in electrical potential between a pH electrode and a reference electrode
. Use standard buffers for calibration, at least three, Since the magnitude of the changes you want to resolve is a trend of -0.002 pH units per year, hiding seasonal changes ten times greater, I can tell you that the voltmeter you should use for measuring that potential should be stable at the order of 100 µV, including determination of offsets, uncertainty and drifts. This without considering the maintenance of electrodes, as the Nernst equation requires. For seawater this is a huge headache, I would say, a bit stupid."

Sagredo : "Alternatives?"
Salviati : "Of course!" - and laughs . "Use light and an indicator dye that changes its color around seawater pH, like thymol blue or m-cresol purple. Their protonation behavior is well known in seawater and you can detect it easily measuring absorbance at two wavelengths in the visible spectra. Remember: narrow the range, increase resolution."

Sagredo : "What about calibration?"
Salviati : "The spectrophotometric detection is inherently calibration free, once you know the behavior of the dye you are using. And should you discover that the temperature-salinity dependent parameters of its mathematical model have been refined, it's just a matter of a few calculations, you still have your spectra stored. Bottom line, it's all about how your spectra are acquired and processed."

Sagredo : "Is there any standard I can compare it with?"
Salviati : "You can prepare your own standard seawater stock, even if I recommend using certified reference material (CRM) for quality assurance from Andrew Dickson's lab .

Sagredo : "I've heard about field effect transistors that..."
Salviati : "Wait, wait. Remember you are measuring a chemical-physical property that pertains to a sample and the sample should be representative of the environment. What if you are looking to something that is not representative of the surrounding environment? What about the interaction between the probe and the sample? Is the item [probe+sample] a new entity you are looking at?"

Sagredo : "Now you are beginning with philosophy..."
Salviati : "Not yet. This is plain metrology. I know, this hasn't been often mentioned. Make it simple: isolate a discrete sample of seawater,  be quick, try not to perturb it too much or measure such a perturbation, track its temperature continuously, always measure a blank for the most precise results, save periodically dark measurements to prevent drifts. Then you should be able to have a precision below 0.001 between replicates.

Sagredo : "And how can I get 0.002 accuracy?"
Salviati : "Don't get obsessed now. Scientists can easily interpolate data and find a trend even if you have a 0.004 accuracy. This means : today you use your instrument to measure seawater pH off, say, the Norwegian coast and in three months you use the same or an identical system to measure pH in the same point. These data should be comparable."

Sagredo : "How can I make it?"
Salviati : "You should assign an uncertainty. Type A evaluation of standard uncertainty may be based on any valid statistical method for treating data while type B evaluation of standard uncertainty is usually based on scientific judgment using all of the relevant information available like previous measurement data, experience with, or general knowledge of, the behavior and property of relevant materials and instruments, manufacturer's specifications, data provided in calibration and other reports. And when I say 0.004 accuracy, I mean that you have measured your offsets respect to the estimate of the true value and this has been given an uncertainty. So, either you have understood and corrected your offset, or that becomes part of the uncertainty."

Sagredo : "Suppose that I could build such a system using off the shelf components and 3D printing fabrication, would you buy it?"
Salviati : "Are you kidding me? A black box? If I was a researcher, first I would evaluate it, then we'll see..."


watered is providing an underway/surface/bench-top spectrophotometric system to measure seawater pH with 0.004 accuracy thanks to proprietary algorithms and signal processing with a low-cost, classic, research oriented design.
Ask for a trial version, send us your study or type of investigation. After a short review we will provide availability of an evaluation system ready to use, assist in deployment, data acquisition and quality control.

Salviati : "Now, if you don't mind, I go and care about my garden. It hasn't been raining for days, and needs to be watered."