Guest post by David Middleton
Introduction
My never-ending search for actual observational data that support the hypothesis of catastrophic anthropogenic ocean acidification (Chicken Little of the Sea) has taken me to offshore Hawaii and Station ALOHA.
The alarmists claim that anthropogenic CO2 emissions have lowered the average pH of the world’s oceans from 8.2 to 8.1 over the last 250 years; and that future emissions will lower the pH by 0.3 to 0.4 over the remainder of this century (Dore et al., 2009). What is the basis of this hypothesis? Systematic measurements of oceanic pH don’t go back much before 1990. Actual pH measurements are few and far between. The oceans have probably absorbed at least half of the anthropogenic carbon emissions of the last couple of centuries. The assertion of CO2-driven ocean acidification appears to he almost entirely based on the rising atmospheric CO2 level. Is this the only basis for the dire warnings of catastrophic ocean acidification? All other things being equal, the addition of CO2 should lower the pH of seawater… However, all other things are seldom equal.
Station ALOHA and the Hawaii Ocean Time-series (HOT)
The Station ALOHA data from the Hawaii Ocean Time-series are very extensive and easily accessible. These data were used by Dore et al., 2009 to demonstrate a ~20-yr trend of apparently CO2-related acidification offshore Hawaii…
At first glance, this appears to be a slam-dunk. The seawater at Station ALOHA have been acidifying in concert with rising atmospheric CO2 for ~20 years. But, looks can be deceiving. One of the tricky things about oceanic pH is that it is very dependent on water temperature, pressure and salinity. Most studies derive pH from Dissolved Inorganic Carbon (DIC or ΣCO2) and Total Alkalinity (TA). DIC is the sum of free CO2 ([CO2(aq)] & [H2CO3]), carbonate ([CO3–]) and bicarbonate ([HCO3-]). TA is the sum of carbonate (2x[CO3–]), bicarbonate ([HCO3-]), tetrahydroxyborate ([B(OH)4-]), hydroxide ([OH-]), hydrogen ([H-]) and other minor compounds. DIC and TA are “conservative quantities” – They are unaffected by pressure and temperature. The ratio of TA:DIC is a very robust measure os the alkalinity/acidity of seawater.
Most of the pH values in Dore et al., 2009 are not measured; they are derived from DIC and TA. While the calculated pH trend appears to show a continuous acidification trend, a plot of TA vs. DIC tells a slightly different story. The alkalinity of the seawater at ALOHA Station actually rose from ~2000 to ~2005, despite steadily rising atmospheric CO2 levels…
Why did the seawater become more alkaline from 2000-2005?
The most likely answer is that the seawater concentration of [CO3–] (carbonate) increased while the concentration of [CO2] decreased during that time interval. This happened despite the fact that atmospheric CO2 levels continued their inexorable rise over that same time period. The ocean at Station ALOHA was actually a net source of atmospheric CO2 for about 5 years.
The reason for the carbonate concentration increase and [CO2] decrease from 2000-2005 is probably related to the slight rise in water temperature over that period and the elevated salinity. The change in water temperature and salinity was also the most likely reason that the 5-year trend of increasing alkalinity was not reflected in the calculated pH trend.
So, the data do support the notion that rising atmospheric CO2 levels can contribute to a lowering of oceanic pH; but that other processes can periodically raise the pH despite the rise in atmospheric CO2.
How Dangerous is Chicken Little of the Sea?
Ocean acidification can only occur if Dissolved Inorganic Carbon (DIC) is rising faster than Total Alkalinity (TA). This nomogram demonstrates the relationship of TA & DIC to pH…
According to Dore et al., 2009, “Over the past 250 years, the mean pH of the surface global ocean has decreased from ≈8.2 to 8.1… This acidification of the sea is driven by the rapidly increasing atmospheric CO2 concentration, which results from fossil fuel combustion, deforestation, and other human activities. Models predict that surface ocean pH may decline by an additional 0.3–0.4 during the 21st century”… A total pH decline of 0.4 to 0.5 (8.2 to 7.7 or 7.6).
I used a linear regression to estimate TA and DIC at ~275 and ~550 ppmv…
If I plot their in situ TA vs in situ DIC and extrapolated it as above (red curve), I get a very strong correlation (R^2=0.72); but I don’t get anything close to a 0.5 to 0.6 pH decline from a doubling of pre-industrial CO2 levels. I get a total decline of 0.16 (8.30 to 8.14) due to a doubling of pre-industrial atmospheric CO2 levels.
The only way I get a pH decline comparable to 0.4 to 0.5 is when I use the TA and DIC values that were normalized to a salinity of 35 (blue curve). This yields a pH decline of 0.44 (8.40 to 7.96); but it is a horrible correlation (R^2=0.05). TA and DIC are highly correlated to salinity(R^2=0.88, 0.74). DIC has a moderate correlation (R^2=0.39) and TA has a weak correlation (R^2=0.12) to atmospheric CO2…
The normalization of TA and DIC to a constant salinity subdues the buffering provided by salinity; while amplifying the acidification effect of increasing CO2. A realistic treatment of salinity, yields an insignificant lowering of pH from a doubling of pre-industrial CO2. Chicken Little of the Sea does not appear to be very dangerous.
Will Chicken Little of the Sea Wreak Havoc on Marine Calcifers?
The Hawaii Ocean Time-series included ~20 years worth aragonite saturation data for Station ALOHA; so we can estimate the effects of atmospheric CO2 changes on aragonite saturation. Ries et al., 2009 experimentally demonstrated the effects of aragonite saturation changes on marine calficers under several CO2 scenarios. So, we can combine Ries’ experimental results with the observational data from Station ALOHA.
I plotted Ries’ CO2 vs. aragonite saturation assumptions and found that a power function trend-line was the best fit. I then plotted the Station ALOHA aragonite saturation vs. MLO CO2 and applied a power function trend-line to extrapolate the aragonite saturation out to about 2900ppmv CO2.
The Station ALOHA data demonstrate a significant difference in the actual effects of CO2 on aragonite saturation relative to the Ries et al., 2009 scenarios…
The observational data show that rising atmospheric CO2 is less detrimental to aragonite saturation levels than was assumed in the Ries experiment.
The Station ALOHA data indicate that marine calcifers have a much higher threshold CO2 level at which the calcification rate drops below its current range than that indicated by Ries…
The observed relationship between atmospheric CO2 and aragonite saturation from Station ALOHA indicates that even the most vulnerable marine calcifer in the Ries study (soft clam) was not adversely affected by CO2 levels below 800ppmv.
References:
Richard E. Zeebe and Dieter A. Wolf-Gladrow
CARBON DIOXIDE, DISSOLVED (OCEAN)
Hawaii Ocean Time-series (HOT)
Station ALOHA Surface Ocean Carbon Dioxide
Dore JE, Lukas R, Sadler DW, Church MJ, KarlDM (2009)
Physical and biogeochemical modulation of ocean acidification in the central North Pacific.
Proc Natl Acad Sci USA 106:12235–12240.
Abrupt Decrease in Tropical Pacific Sea Surface Salinity at End of Little Ice Age
Ries, J.B., A.L. Cohen, D.C. McCorkle. Marine calcifers exhibit mixed responses to CO2-induced ocean acidification. Geology 2009 37: 1131-1134.
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David Middleton says:
November 25, 2011 at 2:36 am
@Dave Wendt on November 24, 2011 at 11:15 pm
“The paper you are trying to recall is Pelejerso’s pH reconstruction of Flinder’s Reef. The [I]Science[/i] paper is available with a free AAAS membership. The data are available from NOAA’s paleoclimatology library.”
Thanks for that!
NOAA PMEL Carbon Programs claims absorption of atmospheric CO2 inputs is only 25%- making this even less of a problem.http://www.pmel.noaa.gov/co2/story/Ocean+Acidification
Anyone ever see any study on the relative impacts on near shore waters from changes in terrestrial organic acid loads (result of afforestation etc), changes in soil water logging due to agricultural draining and 20th century fire suppression?
David Middleton says:
November 25, 2011 at 2:36 am
Pejejero demonstrated a ~0.5 pH oscillation with a ~50-yr period, highly correlated to the PDO.
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David, station ALOHA is one of the main stations for monitoring upwellings……….
“Most of the pH values in Dore et al., 2009 are not measured; they are derived from DIC and TA.”
Are we dealing with a model here? If so, throughout the word “concentration” or “concentrations” are used. Should we not be talking about “activity” or “activities”. There are significant differences in a system as complex as seawater.
Perhaps some things are better left in my mind, but I couldn’t help myself…
http://i39.tinypic.com/16hsolz.jpg
For the last 25 years, Volcanoes Pu’u O’o cone, and Kilauea . has been spewing it’s contents all over the Aloha State.
Need a wider sampling area.
Steve Keohane,
Excellent! I’ll have to steal that, can’t help myself.☺
John Eggert says:
November 24, 2011 at 5:07 pm
I see someone has already gotten onto the “pH is more than 7, so a decrease in pH is not acidification” thing. Can we all agree that lowering pH is acidification and raising it is alkalinization. There are enough issues with this area of science without descending into pedantry. It is very difficult to search for a definition of “acidification” because there is so much out there on ocean acidification. Alkalinization on the other hand is not popular, so definitions are easy to find. Most of them are along the lines of “The process of BECOMING alkaline”. Hence by those definintions, only a base can be acidified and only an acid can be alkalized.
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You sound like an intelligent person and educated in science. There are many such scientists posting on WUWT, and I do not doubt that we could all agree with you, for rational intelligent discussion, especially as it is a well used colloquialism in chemistry.
The problem though is when cretins like Grossman and her ilk (see other thread) get a hold of the term “acidification” and pollute its meaning, using terms like “alarmingly corrosive”.
That’s why it’s always corrected on here – so that people with no education in science who read these threads can see the difference between what the scientists say and what the cretins say.
David Middleton
November 25, 2011 at 2:36 am
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Thanks David!
I had read that paper also, a while back. My main interest at the time was environmental variability in estuary habitats. Most of my brackish aquarium experiments were focused on that. Before I had read this paper, I had assumed that Marine PH was fairly constant, unlike estuary PH ( which is all over the map). I now have a whole set of new experiments I would love to run, once I get the space and time to do them (anything less then 200 L tank size is a waste of time.) I think I can demonstrate that dissolved CO2 is dependent almost entirely on the rate of kariote metabolism, and not atmospheric CO2 concentrations.
BTW, for anyone interested in brackish water Aquariums, I recommend at least 1 watt/liter for lighting, turning the water over at least 6 time/hour, NO BUBBLES, and varying salinity between 10 and 30 ppt on a yearly cycle. I tended to do my weekly water changes (10%) with water that was a few degrees (C) cooler then the tank water ( 25 – 28 C).
Geoff Sherrington says: November 25, 2011 at 2:46 am Addendum.
Sometimes I pick on a graph or paragraph that is not easy to understand – then give it a comment that is misleading in the sense that it could be read a certain way unless you were skilled in the art. Sometimes i do it to see who is reading what how carefully.
Therefore, without prompting, I wish to state that my comment above on the Dore at al graph of 2009 is wrong. On first view it looks as if the reader is invited to do what I did, to wrongly assume that the various pH graphs run on from each other from right margin back to left. Of course, they do not. My apologies to Dr Dore for using his graph as an illustration of the value of clarity in presentation, of which most of us are guilty of forgetting at times.
However, the possibility of leakage over the halocline or whatever you name the discontinuity between shallow waters in the pH 8+ range and deeper ones in the 7.5- range, remains a concern. The position of station Aloha might make it a candidate for mixing from upwelling, but that is conjecture.