Guest lampooning by David Middleton
Hat tip to Latitude…
Human activities are dissolving the seafloor
by the Office of Communications
Nov. 5, 2018 2:07 p.m.
With increasing carbon dioxide from human activities, more acidic water is reaching the deep sea, dissolving some calcite-based sediments, say an international team of researchers.
The seafloor has always played a crucial role in controlling the degree of ocean acidification. When a burst of acidic water from a natural source such as a volcanic eruption reaches the ocean floor, it dissolves some of the strongly alkaline calcite like pouring cola over an antacid tablet. This neutralizes the acidity of the incoming waters and in the process, prevents seawater from becoming too acidic. It can also help regulate atmospheric carbon dioxide levels over centuries to millennia.
As a result of human activities, the level of carbon dioxide in the water is high enough that the rate of calcite (CaCO3) dissolution is climbing, say the researchers. Their findings appear this week in the journal Proceedings of the National Academy of Sciences.
Human activities are dissolving the seafloor…
Where’s that Billy Madison clip? Here it is…
If the seafloor was actually dissolving, it would certainly fix that whole sea level rise thingy.
The paper, Sulpis et al., 2018, is pay-walled and probably not worth $10. Here’s the abstract:
Current CaCO3 dissolution at the seafloor caused by anthropogenic CO2
Oceanic uptake of anthropogenic CO2 leads to decreased pH, carbonate ion concentration, and saturation state with respect to CaCO3 minerals, causing increased dissolution of these minerals at the deep seafloor. This additional dissolution will figure prominently in the neutralization of man-made CO2. However, there has been no concerted assessment of the current extent of anthropogenic CaCO3 dissolution at the deep seafloor. Here, recent databases of bottom-water chemistry, benthic currents, and CaCO3 content of deep-sea sediments are combined with a rate model to derive the global distribution of benthic calcite dissolution rates and obtain primary confirmation of an anthropogenic component. By comparing preindustrial with present-day rates, we determine that significant anthropogenic dissolution now occurs in the western North Atlantic, amounting to 40–100% of the total seafloor dissolution at its most intense locations. At these locations, the calcite compensation depth has risen ∼300 m. Increased benthic dissolution was also revealed at various hot spots in the southern extent of the Atlantic, Indian, and Pacific Oceans. Our findings place constraints on future predictions of ocean acidification, are consequential to the fate of benthic calcifiers, and indicate that a by-product of human activities is currently altering the geological record of the deep sea.
Current CaCO3 dissolution at the seafloor caused by anthropogenic CO2
So… What kind of CO2 was dissolving CaCO3 at the seafloor before GM invented the Suburban? Because CaCO3 did dissolve and it did get redeposited as carbonate rocks way back when atmospheric CO2 was a lot higher than it is today.
The Austin Chalk is contemporaneous to the White Cliffs of Dover. It can be more than 1,200′ thick. It outcrops in the Dallas, Texas area. In South-Central to South East Texas, it is buried to depths >7,000′ below sea level and is a significant hydrocarbon source and reservoir rock. It was deposited at a time when atmospheric CO2 concentrations were 800 to 1,000 ppmv.
Lower Cretaceous CO2 levels ranged from 1,000 to 2,000 ppmv and the seafloor not only didn’t dissolve, but 1,000’s of feet of carbonate rocks were deposited in the in northern Gulf of Mexico basins…
However, there has been no concerted assessment of the current extent of anthropogenic CaCO3 dissolution at the deep seafloor.
That’s because there’s not much CaCO3 at the deep seafloor. The notion that CO2 partial pressure influences the pH of seawater isn’t a new concept. We even studied it in college way back in the Pleistocene (1976-1980); however the phrase “ocean acidification” never appeared in any of my college textbooks.
My Stratigraphy & Sedimentation (Spring Semester 1979) textbook, Principles of Sedimentology by Friedman (yes, that Friedman) and Sanders features an entire section on the relationship between CO2 and pH and how if affects calcium carbonate precipitation and dissolution…
When the pH of seawater decreases, calcium carbonate dissolves. In warm, shallow seas, at a pH of about 8.3, dissolution of aragonite and calcite particles by inorganic processes is almost nonexistent. However, since the classical studies of the Challenger expedition, it has been known that the proportion of calcium-carbonate particles in seafloor sediments decreases as depth of water increases (Table 5-1). Such decrease is particularly rapid at depths between 4000 and 6000 m. Although the reasons for this decrease have been debated, the evidence suggests that calcium carbonate dissolves because the CO2 concentration increases with depth. The control on CO2 appears to be part biological; it results from biological oxidation of organic-carbon compounds. Also, the water masses at greater depth were derived from the polar region; their temperature is lower and the water contains more dissolved CO2. Increased concentration of CO2 is in turn reflected by lower pH, which leads to calcium carbonate dissolution. However, the increase of pressure with depth may also be involved; such increase affects the dissociation of carbonic acid (Eqs. 5-11 and 5-12). The depth at which the calcium-carbonate decreases most rapidly is known as the carbonate-compensation depth, defined as the depth at which the rate of dissolution of solid calcium carbonate equals the rate of supply.
Friedman and Sanders, pages 133-134.
A very thorough, easy to read, description of the relationship between CO2 and seawater pH… However, the phrase “ocean acidification” is notably absent from the entire 300+ pages. How is this possible?
The depth below which CaCO3 ceases to precipitate is call the Carbonate Compensation Depth (CCD). However, the seafloor does not dissolve below the CCD. Below the CCD, seafloor sediments consist of siliceous rather than carbonate muds.
By comparing preindustrial with present-day rates, we determine that significant anthropogenic dissolution now occurs in the western North Atlantic, amounting to 40–100% of the total seafloor dissolution at its most intense locations. At these locations, the calcite compensation depth has risen ∼300 m. Increased benthic dissolution was also revealed at various hot spots in the southern extent of the Atlantic, Indian, and Pacific Oceans.
First off… There’s no way to compare preindustrial with present-day rates. There are no measurements of preindustrial rates. Estimates of preindustrial rates are based on the rise in atmospheric CO2… Which they assume is unprecedented.
Scientific Reports volume 4, Article number: 5261 (2014)
Larger CO2 source at the equatorial Pacific during the last deglaciation
Kaoru Kubota, Yusuke Yokoyama, Tsuyoshi Ishikawa, Stephen Obrochta & Atsushi Suzuki
While biogeochemical and physical processes in the Southern Ocean are thought to be central to atmospheric CO2 rise during the last deglaciation, the role of the equatorial Pacific, where the largest CO2source exists at present, remains largely unconstrained. Here we present seawater pH and pCO2 variations from fossil Porites corals in the mid equatorial Pacific offshore Tahiti based on a newly calibrated boron isotope paleo-pH proxy. Our new data, together with recalibrated existing data, indicate that a significant pCO2 increase (pH decrease), accompanied by anomalously large marine 14C reservoir ages, occurred following not only the Younger Dryas, but also Heinrich Stadial 1. These findings indicate an expanded zone of equatorial upwelling and resultant CO2 emission, which may be derived from higher subsurface dissolved inorganic carbon concentration.
Kubota et al, 2014 found…
pH and pCO2 reconstruction
Using our revised calibration, we reconstructed pH from our new δ11B measurements on Tahitian corals, as well as from previously reported data11 from both the Marquesas and Tahiti, and the overall result is consistent with the WEP foraminifer δ11B variations10 (Fig 3a and b). The oldest coral sample, dated to 20.7 ka BP during the last glacial maximum (LGM), exhibits a relatively high pH (8.26). From 15.5 to 9.0 ka BP, pH is generally constant within uncertainty (8.15–8.22) and consistent with the preindustrial value of 8.20. Four notable pH excursions are associated with HS1 and the YD. Two of our samples exhibit anomalously low pH at the end of HS1 (8.13 at 15.15 ka and 8.09 at 14.99 ka BP), in addition to those at end of the YD at the Marquesas11. The low pH following HS1 had been previously undetected at this location. Calculation of pCO2 (see Methods) reveals deglacial values significantly above those of the atmosphere (Figs. 3c and 4a). Conversely, ΔpCO2during last glacial and the early Holocene was nearly zero, suggesting air-sea CO2 equilibrium.
Periods of anomalously low pH and high pCO2 near the transitions from Heinrich Stadial 1 (8.08-8.15 & 300-350 μatm) to the Bølling/Allerød, during the Bølling/Allerød interstadial (8.15-8.20 & >300 μatm) and at the onset of the Holocene (8.02-8.10 & 350-420 μatm)… Sounds kind of precedented to me.
Our findings place constraints on future predictions of ocean acidification, are consequential to the fate of benthic calcifiers, and indicate that a by-product of human activities is currently altering the geological record of the deep sea.
We know what the fate of benthic calcifiers will be if the CCD shoals (becomes shallower)… They become extinct and then recover (they move).
Here’s a “funny thing” about the PETM benthic foraminifera “mass extinction”: The benthic foram’s rapidly recovered from their extinction (literally):
Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 186–200.
Extinction and recovery of benthic foraminifera across the Paleocene–Eocene Thermal Maximum at the Alamedilla section (Southern Spain)
L. Alegret , S. Ortiz E., Molina
A b s t r a c t
A complete succession of lower bathyal–upper abyssal sediments was deposited across the Paleocene–Eocene Thermal Maximum (PETM) at Alamedilla (Betic Cordillera, Southern Spain), where the benthic foraminiferal turnover and extinction event associated with the negative carbon isotope excursion (CIE) across the PETM have been investigated. Detailed quantitative analyses of benthic foraminifera allowed us to distinguish assemblages with paleoecological and paleoenvironmental significance: pre extinction fauna, extinction fauna, survival fauna (including disaster and opportunistic fauna) and recovery fauna. These assemblages have been associated with significant parts of the δ13C curve for which a relative chronology has been established. The correlation between the benthic turnover, the δ13C curve, the calcite and silicate mineral content, and sedimentation rates, allowed us to establish the sequence of events across the PETM. At Alamedilla, the benthic extinction event (BEE) affected ~37% of the species and it has been recorded over a 30-cm-thick interval that was deposited in c.a. 10 ky, suggesting a gradual but rapid pattern of extinction. The beginning of the BEE coincides with the onset of the CIE (+0 ky) and with an interval with abundant calcite, and it has been recorded under oxic conditions at the seafloor (as inferred from the benthic foraminiferal assemblages and the reddish colour of the sediments). We conclude that dissolution and dysoxia were not the cause of the extinctions, which were probably related to intense warming that occurred before the onset of the CIE.
The BEE is immediately overlain by a survival interval dominated by agglutinated species (the Glomospira Acme). The low calcite content recorded within the survival interval may result from the interaction between dilution of the carbonate compounds by silicicate minerals (as inferred from the increased sedimentation rates), and the effects of carbonate dissolution triggered by the shoaling of the CCD. We suggest that Glomospira species (disaster fauna) may have bloomed opportunistically in areas with methane dissociation, in and around the North Atlantic. The disaster fauna was rapidly replaced by opportunistic taxa, which point to oxic and, possibly, oligotrophic conditions at the seafloor. The CCD gradually dropped during this interval, and calcite preservation improved towards the recovery interval, during which the δ13C values and the calcite content recovered (c.a. +71.25 to 94.23 ky) and stabilized (N94.23 ky), coeval with a sharp decrease in sedimentation rates.
Benthic foram’s appear to have an even higher recovery rate from extinction than the Incilius genus of toads…
The shoaling of the lysocline during the PETM is represented by the 30 cm thick band of red clay from 13.4 to 13.7 m on the lithology column in figure 8. When the lysocline and carbonate compensation depth (CCD) briefly shoaled, the transition from calcareous to siliceous ooze moved shoreward. When the CCD dropped back down to its pre-PETM depth, the transition from calcareous to siliceous ooze moved seaward… Leaving a 30 cm thick layer of red clay in the middle of a thick marl sequence. Rising and falling sea level could have left a similar layer of red clay.
The benthic foram’s above and below the red clay horizon ceased to exist at that location for about 70,000 to 220,000 years. However, the fact that at least some of them returned to that location after the PETM might indicate that the benthic foram “mass extinction” was more of a benthic foram depositional “mass relocation,” rather than a true extinction. I’ll let “Farmer Fran” explain how the benthic foram’s recovered from extinction:
Some authors actually have seriously referred to the PETM benthic foram extinction as a “mass extinction”… And they still expect to be taken seriously?
Excessive carbonate undersaturation of the deep ocean would likely impede calcification by marine organisms and therefore is a potential contributing factor to the mass extinction of benthic foraminifera at the P-E boundary. Although most plankton species survived, carbonate ion changes in the surface ocean might have contributed to the brief appearance of weakly calcified planktonic foraminifera (6) and the dominance of heavily calcified forms of calcareous algae (37). What, if any, implications might this have for the future? If combustion of the entire fossil fuel reservoir (~4500 GtC) is assumed, the impacts on deep-sea pH and biota will likely be similar to those in the PETM. However, because the anthropogenic carbon input will occur within just 300 years, which is less than the mixing time of the ocean (38), the impacts on surface ocean pH and biota will probably be more severe.
Good fracking grief!!! WTF is “the entire fossil fuel *reservoir*”? Last I checked, most fossil fuel (coal) isn’t in a reservoir (coal bed methane isn’t a coal reservoir) and the fossil fuels that do occupy reservoirs (petroleum and natural gas) occupy many thousands thousands of different reservoirs.
Accuracy not withstanding… So, if we burned all of the fossil fuels that Zachos et al think exist, the effects on deep-sea biota might be as bad as the PETM and the surface effects might be worse… if we burn all of those fossil fuels within 300 years. And? What’s the problem here? Is the field of speculative non sequitur reasoning now an academic discipline of science? Oh wait… Yes it is. It’s what climate science has become since 1988.
Chicken Little of the Sea will pretty well only be an issue, where it is already an issue… mostly in areas of strong upwelling.
The Earth isn’t behaving any differently over the past 150 years than it has behaved over the past [fill in the blank] years. Same as it ever was…
Dennen, Kristin O. and Paul C. Hackley Definition of Greater Gulf Basin Lower Cretaceous Shale Gas Assessment Unit, United States Gulf of Mexico Basin Onshore and State Waters. Search and Discovery Article #10429 (2012)
Adapted from oral presentation at AAPG Annual Convention and Exhibition, Houston, Texas, April 10-13, 2011
Sulpis, Olivier, Bernard P. Boudreau, Alfonso Mucci, Chris Jenkins, David S. Trossman, Brian K. Arbic, Robert M. Key. Current CaCO3 dissolution at the seafloor caused by anthropogenic CO2. Proceedings of the National Academy of Sciences Oct 2018, 201804250; DOI: 10.1073/pnas.1804250115
See these two posts for detailed Chicken Little of the Sea references: