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Oceans Giving Back a Little C02. The Good News from Bud Bromley’s Zoom Webinar on ANZAC Day

By jennifer
April 27, 2025

Carbon dioxide is indeed the 'stuff of life', underpinning photosynthesis, boosting plant growth, enhancing agricultural yields, and enabling practical applications in industry. While discussions so often focus on its role in climate change, CO₂’s contributions to life in ecosystems is profound and undeniable, making it a cornerstone of biological and other planetary processes.

CO₂ is a central component of the global carbon cycle, linking the atmosphere, oceans, land, and biosphere. It is cycled through processes like respiration, decomposition, and calcification, as in the Thermal-Acid Calcification Hypothesis (TAC).

Indeed, the vast ocean carbon reservoir, some 50-60 million gigatons of carbonates represents a colossal ‘hoard’ built by calcification over eons, dwarfing atmospheric and terrestrial carbon pools. The release of even a tiny fraction of this carbon as CO₂ due to ocean warming is arguably good news.

In my zoom webinar with Bud Bromley on Friday afternoon (Anzac Day in Australia), it was hypothesised that the oceans are indeed the origin of the increasing atmospheric carbon dioxide levels. Further Bud Bromley explained how minuscule this increase is, only measurable because of the sophisticated equipment and non-standard methodology developed by Charles Keeling involving measurement taken at night some 3,600 metres (11,000 feet) up a volcano in the central northern Pacific.

I really appreciated the detail that Bud Bromley went to in our zoom webinar, to explain how dry samples are taken and reported as molecules per million molecules of air (ppm) after water vapour is removed. For example, 420 ppm means 420 CO₂ molecules per million dry air molecules.

Water vapor is removed because its concentration varies significantly (0–4% of air volume) due to humidity, temperature, and weather, and so the inclusion of water vapour would not make for such a neat seasonal and annual pattern in CO₂ increase, particularly given C02 is such a minuscule percentage of air relative to other gases such as oxygen and water vapour.

Bud Bromley repeated made the point that the annual atmospheric increase as measured at Mauna Loa is currently only a fraction of the total atmospheric concentration that is measured in parts per million. The increase is some 0.5% annually that is one third of the seasonal variation.

Bud Bromley is not only a chemist, with a significant knowledge of ocean chemistry, he is also a keen scuba diver, and our discussion began with reference to Boyle’s Law that is why scuba divers must not hold their breathe on ascent least they explode their lungs, and from that there was explanation of the relevance of Boyle’s Law and the Ideal Gas Law and Henry’s Law to knowing that current increases in atmospheric carbon dioxide are natural, and from the vast reservoir of carbon in our oceans.

It is surprising that this fundamental law, Henry’s Law, critical to understanding how CO₂ solubility in the oceans affects atmospheric levels, that Henry’s Law is not considered relevant by the IPCC reports, or even discussed in the report by Will Happer’s C02 Coalition authored by Ferdinand Engelbeen that claims to provide multiple lines of proof that human emissions are responsible for increasing atmospheric concentrations, while their hypothesis is that the ocean is a net sink.

Henry’s Law is key to understanding how much gas dissolves in a liquid, like CO₂ in seawater. It says the amount of gas dissolved is proportional to the pressure of that gas above the liquid:

C = k * P

C is the concentration of dissolved gas, P is the gas’s pressure in the air, and k is a constant that depends on the gas and temperature. If the ocean warms due to natural changes in circulation, k gets smaller, meaning less CO₂ stays dissolved, and more escapes to the atmosphere.

This is central to my hypothesis, leveraging Henry’s Law directly by linking temperature-driven changes in calcite solubility to shifts in seawater CO₂ solubility.

There have been various claims made, not during the zoom webinar, but on social media etcetera since I've begun promoting TAC, that Henry’s Law has limited direct application because of the ocean’s complex, non-equilibrium chemistry, at last acknowledging this may be drive by carbonate buffering, calcium supersaturation, and biotic processes. For sure, true equilibrium is unattainable due to continuous inputs (e.g., limestone dissolution, runoff) and the dynamic interplay of forward and reverse reactions. However, dismissing Henry’s Law is nonsense, as it remains critical to understanding the air-sea flux, in combination with kinetic and carbonate systems.

We had just over 80 guests register for the zoom webinar that was the fourth in my new series Towards a New Theory of Climate Resilience. Just under 40 joined the live event.

I am so grateful to everyone who did joined in. As something of a last minute change of plan, I made the second hour more panel discussion than Q&A, as I was so pleased to see Ferdinand Engelbeen join the webinar and I was keen to understand in more detail his disagreement with Bud Bromley’s thesis; the disagreement has been long running and at times acrimonious. I was keen to understand this, because Bud's thesis focused on Henry's law are critical to my emerging new Theory of Climate Resilience. This new theory will not focus on CO₂ as a driver of climate (not at all), but nor will I dismiss CO₂ because it is fundamental to life on Earth and its abundance in the atmosphere and the oceans does vary with climate. This is important to understand if we are curious about life on Earth, and how life changes sometimes dramatically because of natural climate cycles.

I was interested to hear that Ferdinand did not dispute Bud’s figures or engage with Henry’s Law or other aspects of the ocean's physical chemistry that was the focus of this zoom webinar. Rather Ferdinand continued with his narrative that essentially draws a correlation between human emissions of CO₂ and increasing atmospheric levels of CO₂ somewhat complicated by respiration from northern hemisphere forests as a source while insisting, despite the Mauna Loa data, that oceans are a net sink. Ferdinand's report can be downloaded from the CO₂Coalition website and is entitled 'The Human Contribution to Atmospheric Carbon Dioxide' (December 2024).

Then there were Ferdinand Engelbeen’s comments during the seminar about oxygen, as though it is only produced by northern hemisphere forests. In fact, phytoplankton’s oxygen production is more significant, as their dual role in photosynthesis and calcification significantly influences ocean degassing, potentially overshadowing abiotic processes like TAC in productive regions like the Great Barrier Reef that is also a net emitter of carbon dioxide as I will explain in a future webinar.

The interplay of external (e.g., solar-driven temperature changes) and internal (e.g., phytoplankton blooms, ocean circulation) drivers further complicates our understanding of these important processes. Seasonal cycles, as emphasised by TAC, are critical, but longer-term drivers (e.g., upwelling, climate oscillations) also shape degassing. Phytoplankton’s dominance in oxygen production is under appreciated, certainly their role in public discourse is largely ignored compared to forests. These are all topics I want to explore going forward as I further develop my new Theory of Climate Resilience.

The next zoom meeting as part of this series is planned for Saturday 24th May across three different time zones with three different sessions, more details to be announced in the next week or so. This webinar on 24th May will be less formal in structure than my interview with Bud Bromley, or the panel session than followed; at least that is the plan. (I have received various emails requesting more potential for interaction between participants for future webinars.)

Also, I have tentative agreement from Ferdinand Engelbeen for a webinar on Saturday 12 July, at which I will attempt to understand his perspective that so far, I mostly see as unsophisticated curve-fitting though I do appreciate that his perspective accords with not only the C02 Coalition reports but also the IPCC. I appreciate that my view, and also Bud Bromley's, are in the minority.

I am grateful to Bud Bromley, and many others including Brendan Godwin, Alex Pope, Robert Weller, Case Smit, Philip Mulholland, Ric Werme, Christopher Game, Ivan Kennedy who did join the zoom webinar on Friday and took the time to consider our very different perspective.

William Henry, confirmed by John Dalton and thousands of other scientists since them, discovered that a gas partitions between a liquid and a volume of gas in contact with that liquid, and that the partition ratio is a physical property like a boiling point or specific heat; these are properties which are not changed by the amount of matter present. Henry demonstrated that the partition ratio is a function of the absolute temperature of the liquid. That is, colder liquids absorb more gas than they emit and warmer liquids emit more gas than they absorb.

In other words, adding carbon dioxide to the atmosphere by burning fossil fuels does not increase the concentration of carbon dioxide in the atmosphere. A carbon dioxide concentration in air which exceeds the Henry’s Law ratio for a given water temperature will be absorbed by water.

Any carbon dioxide removed from air will be replaced from water and water containing surfaces everywhere until the Henry’s ratio is restored for the local water temperature. Life evolved under this dynamic condition.

Quoting Bud Bromley.

For further reading Bud recommends: https://henryslaw.org
There is also more information at https://budbromley.blog/

When Bud and I agreed on the date and time (2pm on 25th April) I did not realise that was ANZAC Day afternoon. I did begin our zoom webinar acknowledging the sacrifices of my grandfathers, and also my uncle John Edward Turnour.

ANZAC Day is a national day of remembrance for those who served and died in wars, conflicts and peace keeping operations. My great uncle John Edward Turnour, enlisted along with three brothers on 1st September 1914. He died from wounds in a field in Belgium/Polgon Wood on 28th September 1917 and he is buried at a Commonwealth War Cemetery in Flanders.

I am sure that John Edward Turnour would not have minded us discussing climate science on ANZAC Day afternoon. He would not approve, though, of the Australian Bureau of Meteorology, or equivalent institutions in the UK, US and Europe, also changing the historical temperatures from back then. For sure it was hotter in many places for weeks at a time during the 1930s, and there were some very cold winters during the 1940s.

One of the most pervasive effects of weather on World War I was the relentless rain. At the Western Front, the relentless rain transformed trenches into mud and misery. Torrential rainfall in 1915, 1916 and 1918 had a decisive role in major battles such as Verdun and the Somme, contributing to the death of over a million soldiers. Many times, large ridges of high pressure over Russia would produce extreme cold in the eastern part of Europe and result in a repetitive pattern of low pressure systems for western Europe, bringing little to no sunshine and heavy rainfall.

Good Causes

Comments

  1. Jim,

    I have been reading the link to Pieter Tans description of the pitfalls of the 13C/12C ratio, that is a very interesting work.

    Indeed, there are periods that δ13C goes up while there still is an increase in CO2, as my plot for the period 1999-2001 shows: during a La Niña. The point is that it is not the oceans that make the difference, but still it is vegetation that is dominant.

    Thanks to very accurate O2 measurements, we know that plants were even a net source of CO2 (at below -20 per mil δ13C) during months in the 1998 strong El Niño, but start to be a strong absorber (at over 3 PgC/year with over +20 per mil δ13C) during the adjacent strong La Niña.

    See Figure 7 at the last page of:
    http://www.bowdoin.edu/~mbattle/papers_posters_and_talks/BenderGBC2005.pdf

    That makes that the oceans may have had a small contribution in direct influence of +1 per mil (compared to the atmosphere) by absorbing some 1 PgC CO2 extra, but the much stronger isotopic difference caused by the extra CO2 uptake in vegetation is the main cause of the temporary increase in δ13C.

    All together, the fact that one can calculate the δ13C drop with an apparent "constant" source of -13 per mil δ13C is no proof at all that such a source exists, only that the proven constant increasing source of -25 per mil δ13C fossil fuel CO2 is diluted with a constant stream of deep ocean δ13C at -6.5 per mil, something Pieter Tans (who obviously used the Bern model) doesn't take into account.

    The remaining variability around the trend is largely caused by vegetation that was a small source of CO2 before the 1990's and an increasing sink after that, with relative large variability's caused by temperature and drought (El Niño / La Niña).

    If I ever have the time, I will work out the combination of fossil fuels (at -25 per mil), the 40 PgC/year deep ocean return (at -6.5 per mil) plus the ocean / vegetation (at +24 or -24 per mil) emissions / uptake further out for the period 1997-2001...

    *****

    Jennifer Marohasy here about to post a note from Jim that he has been unable to post, perhaps because of the age of this post comments have closed.

    JIM WRITES:

    Ferdinand,

    I see that you are relying on the Bender et al (2005) paper for your argument relating to the period 1999-2001 (a period of back-to-back La Niña events). Here is an interesting quote from the paper:

    “At non El Niño times, the balance of evidence suggests that the large ocean amplitude in sequestration rates calculated with 1-year averaging (Figure 7), and ocean-land antiphasing, are artifacts.”

    Figure 7 is, of course, the graph that you referenced so this comment shows that the authors do not have a lot of confidence in their model for the period 1999-2001 (i.e. “non El Niño times”). Further, the issue of “sequestration rates” remains contentious to this day. This is shown by the Global Carbon Budget data (https://globalcarbonbudget.org/), which helpfully include the calculation of an annual “budget imbalance” based on multiple published models.

    Problems with ‘climate science’ models also include the inability to match observed inter-annual changes in atmospheric δ13C (e.g. van der Velde et al (2013), https://agupubs.onlinelibrary.wiley.com/doi/10.1002/gbc.20048). Interestingly, Tans was a co-author on both this paper and on Bender et al (2005).

    In the case of your model, it is clear that it (the red line on the plot below) fails because it does not match observations at any time starting from soon after the fixed start date in 1860 through to about 1980 (as you confirmed at WUWT). On the other hand, the assumption of a constant δ13C of -13‰ for the incremental atmospheric CO2 throughout the whole period does a far superior job at matching the observations (the green diamonds, which I computed using only published CO2 values, a starting δ13C value of -6.5‰ and -13‰ for all the incremental CO2 thereafter). I then plotted the graph at a scale to match and overlay your plot:
    https://i.postimg.cc/bNfWkCBj/d13-C-comparison.jpg.

    It is still not clear to me whether or not you accept the following position. If we have 2 pairs of atmospheric CO2 and δ13C measurements, at the same location, with an increase in CO2 between them, we can easily derive the average net δ13C of the incremental CO2 within the limitations of the uncertainty in the measurements. The calculated δ13C value is the average for the incremental CO2 between the two pairs of measurements and is based on the 13C mass balance equation as required for stable isotopes.

    The resultant δ13C value is data; it is not an estimate, or a coincidence, or is it based on any assumptions other than the validity of the measurements. There is an immaterial approximation in the general mass balance equation and this can be confirmed as insignificant by converting δ13C back to the actual 13C/12C ratio. It is, obviously, a net value and does not tell you the make-up of sources and sinks that could be involved in the increasing CO2, but it does provide an absolute constraint on any models that are proposed.

    If we have multiple measurements of atmospheric CO2 and δ13C at a single location, which all show the same average net value over long periods of time, this would provide a further constraint on potentially valid physical models. The likelihood of the physical mix of sources and sinks changing significantly while the average δ13C value pertaining to the source/sink ‘mix’ (as you call it) remains constant would be rather unlikely and would certainly require clear justification (evidence) to support the validity of the model.

  2. Thanks Peter for your wise words...

    I know Cohenite already many years from discussions in the (far) past, he/she barks a lot but doesn't bite...

    Anyway you are right that it doesn't any good at any scientific discussion to use such "arguments", but it reflects more badly on those who use them than those who are the target...

    BTW, I have been hardened in this kind of accusations like "killing children for the next generations" in discussions with Greenpeace adepts about the use of chlorine/PVC, where I was working at that time (1990's) and defending my job against the false allegations of Greenpeace...

  3. Cohenite,

    If 13% of all subairial volcanoes (including diffuse emissions) are monitored and all of them had a isotopic "fingerprint" between zero and -7 per mil δ13C, depending of the origin of the CO2 (subduction of carbonates or deep magma) that is a quite representative sample of all volcanoes in this world.

    The possibility that CO2 emissions from volcanoes are as low in δ13C as fossil fuel emissions at -24 per mil is as good as non-existing. Let it be that volcanic emissions were as high or higher than of the human use of fossil fuels and start at exact the same moment and strength as human emissions. And what happens then with human emissions? Disappear in space?

    What Segalstad said is highly misleading, as it is not the δ13C difference between atmospheric and volcanic CO2 that is important (indeed volcanoes can't be the cause of the rapid δ13C decline in the atmosphere!), it is the much lower δ13C of fossil fuels at -24 per mil that is important and proves that fossil fuels are the cause of the decline of δ13C in the atmosphere...

  4. Ferdinand,

    I have been away for a few days. I really must respond to some comments made by you above (https://climatelab.com.au/2025/04/oceans-giving-back-a-little-c02-the-good-news-from-bud-bromleys-zoom-webinar-on-anzac-day/#comment-779022).

    First, a relatively minor point, but an incorrect statement nevertheless. The link to my WUWT comment was to my “simple model”, as I linked here: https://wattsupwiththat.com/2025/04/10/whose-co%e2%82%82-is-it-anyway-ocean-fizz-or-smokestack-blame/#comment-4061379. You claim that “What you have plotted in the reference at WUWT is a comparison between δ13C and 1/[CO2] … ”. This is a false statement. My “simple model” comprised 4 plots, showing trends of atmospheric CO2 and δ13C, both plotted against time. I do not show 1/CO2.

    Elsewhere, I do make use of Keeling plots, which are based on plotting 1/CO2 against δ13C reflecting 13C mass balance principles, but not in the linked comment that you specifically referenced.

    My second point is with respect to my observation that “This is the situation mentioned by Pieter Tans: atmospheric δ13C is increasing at the same time as atmospheric CO2 is increasing.” You respond to this by saying “Which is obviously not true: δ13C is rapidly dropping everywhere …”. This is a serious accusation, because it suggests that my comment was a lie. In the linked comment at WUWT, however, I explicitly quoted from Tans’ paper, which made it unambiguously clear that he (and I) were referring to a situation that “sometimes” occurs.

    The long term trend in atmospheric δ13C (i.e. after removing the seasonal cycle) is predominantly towards lower values as indeed it must be; the average net value is -13‰ and the atmosphere is around -8‰. However, what Tans and I were referring to were the short periods when the net δ13C is increasing at the same time that the net CO2 is increasing. The net value of δ13C of the increasing atmospheric CO2 during such periods must be higher than the value for the atmosphere at that time.

    Pieter Tans agrees and refers to this important observation as the δ13C trend “go[ing] in the wrong direction” reflecting the fact that, generally, but not always, the CO2 and δ13C trends are in opposite directions. He makes the comment: “The figure suggests that terrestrial variations are the largest component of the observed annual variability but that the oceans also contribute”.
    https://www.researchgate.net/publication/358831874_REMINISCING_ON_THE_USE_AND_ABUSE_OF_14_C_AND_13_C_IN_ATMOSPHERIC_CO_2.

    This switching in trends is even demonstrated by your own plot here:
    https://www.ferdinand-engelbeen.be/klimaat/klim_img/temp_dco2_d13C_mlo.jpg. Note that these data have had the seasonal cycle removed prior to taking the derivative. Look at the period just before 2000, but following the 1997-1998 El Niño. CO2 growth remains positive throughout and yet the δ13C trend switches from negative to positive for a short period, coincident with the 1998-1999 and 1999-2000 strong La Niña events.

    Such events are known to correspond to periods where more upwelling of colder waters is occurring. This observation strongly supports the contention that, at least during these events, oceanic effects (in the form of the El Niño-Southern Oscillation) are a significant factor in variations to the δ13C value of the increasing atmospheric CO2.

  5. It has been quite difficult to follow the discussion over isotopic differences and origins but proper scientific discourse will inevitably produce a variety of opinions, especially when lack of sufficient quality data, especially over geological time, and uncertainty over physical and biological processes exists.

    However I find it most unwholesome that many of those writing in this section - and other sections - feel that it is quite ok to denigrate those with whom they disagree. In this case Ferdinand seems to have been the main target of ridicule and hostile comments as the quotes below illustrate.

    "That this made-up data that is a disgrace, that this is your final refuge, you are a disgrace."

    "When are you going to fess up Ferdy and admit you’re really Michael mann."

    “Comparing apples with oranges…” A balanced diet has both Ferdy."

    "First time you’ve made sense Ferdi."

    "Lol. You’re slippery Ferdy."

    Despite this infantile treatment he has been writing at some length with his reasoning and trying to respond positively even to those who disparage and ridicule him .

    In other blogs we have the perennial pest who appears to have no scientific knowledge whatsoever and whose main job seems to be is to call anyone she (I assume it is she) disagrees with to be funded by the oil industry which therefore by her perverse logic automatically makes us wrong.

    Those concerned should grow up and behave like responsible adults.

  6. "That means that no known volcano in the current world, with 13% of all subaireal volcanoes measured,"

    Lol. You're slippery Ferdy. I repeat:

    "In the absence of statistically significant isotope determinations for each volcanic province contributing to the atmosphere, this makes CO2 contributions of volcanic origin isotopically indistinguishable from those of fossil fuel consumption. It is therefore unsurprising to find that Segalstad (1998) points out that 96% of atmospheric CO2 is isotopically indistinguishable from volcanic degassing. So much for the Royal Society’s unexplained “chemical analysis”. If you believe that we know enough about volcanic gas compositions to distinguish them chemically from fossil fuel combustion, you have indeed been mislead. As we shall see, the number of active volcanoes is unknown, never mind a tally of gas signatures belonging to every active volcano. We have barely scratched the surface and as such, there is no magic fingerprint that can distinguish between anthropogenic and volcanogenic sources of CO2.”

    Segalstad's Unknown vs Ferdy's 13%. Mmmm.

    And that 13% does not include diffuse CO2 emissions.

  7. Cohenite,

    Magmatic CO2 indeed is 13C depleted, but by far not that deep as what is CO2 from fossil fuels or recent organics.

    All volcanic vents that were examined for 13C/12C ratio, both from the plume as for the more diffuse outgassing are between zero (for subduction volcanoes) and -7 per mil δ13C (for deep magma volcanoes). The current atmosphere dropped from -6.4 +/- 0.2 per mil δ13C over the past 600 years in ice cores to currently -8.2 per mil since about 1850.

    That means that no known volcano in the current world, with 13% of all subaireal volcanoes measured, has contributed to the enormous drop of δ13C in the atmosphere, neither in the similar δ13C drop in the ocean surface or vegetation. No matter how much the CO2 emissions out of volcanoes were and are.

    Further, the measurements around Mount Etna were both for the plume as for more diffuse emissions. They had an elegant solution to make a differentiation between environmental and volcanic CO2: they measured the CO2/SO2 ratio in the volcanic plume and then measured SO2 everywhere to estimate the CO2 emissions from direct and diffuse sources alike caused only by the volcano and the total underground around the volcano...

    Indeed there were periods in the history of the earth that volcanoes were the main source of CO2 in the atmosphere. In the pas several million years that isn't anymore the case, as CO2 levels did drop from 2000-1000 ppmv during the Cretaceous to 180-300 ppmv over the past 800,000 years.

    Last but not least, even if current volcanoes and volcanic fields are emitting 10 time more CO2 than previously estimated, did that increase since 1850? If one looks at volcanic eruptions, the recent period was less active that e.g. during the Little Ice Age, when far more eruptions were noticed. As eruptions may be the top of the emissions pyramid, the diffuse emissions probably are in ratio to full volcanic eruptions...

  8. "If you mix wine with 10% alcohol with stronger wine with 12% alcohol, you never will see that the end result is below 10% alcohol…"

    First time you've made sense Ferdi.

    The C12/C13 ratio is the Suess Effect, named after the chemist who described the change in this ratio, Hans Suess. Suess dealt specifically with C14 ratios but the principle is the same. But Suess estimated that fossil fuel CO2 accounted for less than 1% of carbon isotope reservoir contamination. In other words, Suess acknowledged that other sources of contamination played a much larger role (Suess, 1955, p.416), but authors, such as Fergussen (1958), Keeling (1979), Tans (1979), Cleveland & Morris (2006), ignored this rather important point. To which we can add Ferdy.

    "The misuse of the Suess Effect as a fossil fuel fingerprint instead of an empirical standard for the correction of carbon dating contamination, lead to an initially idiosyncratic expansion of this concept by Keeling (1979), who sought to include 13C depletion of vegetation and its effect on the atmosphere. The atmosphere is enriched in 13CO2 by the process of photosynthesis, which favours the assimilation of 12C into plant tissue during growth (Furquhar et al., 1989). This is used to differentiate between terrestrial and oceanic CO2 sources (Keeling et al., 2005), and the concept, proposed by Craig (1954), is actually older than Suess' original research. Moreover, plant based fossil fuel derivatives are therefore considered to be 13C depleted. Following this line of logic, fossil fuel emissions, being derived from plants, should be 13CO2 depleted as well. However, when the Keeling (1979) article expanded its internal definition of the Suess Effect to include this observation, it was once again to the exclusion of volcanic influence.

    In point of fact, magmatic carbon is, for the most part, 13C depleted. This is solidly confirmed by numerous studies of deep mantle rocks (Deines et al., 1987; Pineau & Mathez, 1990; Cartigny et al., 1997; Zheng et al., 1998; Puustinen & Karhu, 1999; Ishikawa & Marayuma, 2001; Schultz et al., 2004; Cartigny et al., 2009; Statchel & Harris, 2009) as well as mid-oceanic ridge outgassing (De Marais & Moore, 1984). Moreover, 13C depletion of volcanic emissions is so well known that Korte and Kozur (2010) explore volcanism, amongst other possible causes, in search of an explanation for atmospheric depletion of 13C across the Permian-Triassic boundary. Although many significant carbonates are not 13C depleted, they are eventually subducted along with organic carbon sources depleted in 13C. Nevertheless, the emissions of continental margin and back arc volcanoes that source a significant proportion of their carbon from subducted volatiles, remain 13C depleted (eg. Giggenbach et al., 1991; Sano et al., 1995; Hernández et al., 2001). Thus, as plants continue to enrich the atmosphere in 13C while supplying the 13C depleted kerogen that is subducted into the mantle, volatiles failing to return to the surface may cause the mantle to become increasingly 13C depleted over time. Moreover, the significant proportion of volcanic carbon dioxide that diffuses through the soil (Gerlach, 1991) has its carbon isotope chemistry further contaminated by 13 depleted biogenic soil carbon (Hernández et al., 2001).

    Both tectonic and volcanic CO2 are magmatic and depleted in both 13C & 14C. In the absence of statistically significant isotope determinations for each volcanic province contributing to the atmosphere, this makes CO2 contributions of volcanic origin isotopically indistinguishable from those of fossil fuel consumption. It is therefore unsurprising to find that Segalstad (1998) points out that 96% of atmospheric CO2 is isotopically indistinguishable from volcanic degassing. So much for the Royal Society's unexplained "chemical analysis". If you believe that we know enough about volcanic gas compositions to distinguish them chemically from fossil fuel combustion, you have indeed been mislead. As we shall see, the number of active volcanoes is unknown, never mind a tally of gas signatures belonging to every active volcano. We have barely scratched the surface and as such, there is no magic fingerprint that can distinguish between anthropogenic and volcanogenic sources of CO2."

    As to those volcanic emissions of CO2, which you dismiss as insignificant, no offence, but I prefer this gentleman's view:

    https://www.livescience.com/40451-volcanic-co2-levels-are-staggering.html

  9. Cohenite,

    Please...

    δ13C only shows the ratio of 13C to 12C.
    In itself, that doesn't show how large the flows are, but it proves that volcanoes are NOT the cause of the enormous δ13C decline since about 1850. Impossible.

    If you mix wine with 10% alcohol with stronger wine with 12% alcohol, you never will see that the end result is below 10% alcohol...

    In the case of the δ13C of the atmosphere, there is one real, known source of low-13C (at average -25 per mil δ13C): human emissions and one probable source: vegetation (at -24 per mil δ13C), but only if there is more decay of vegetation than increase in vegetation (at +24 per mil δ13C).

    The oxygen balance and the NASA satellites show that the earth is greening, thus vegetation is faster growing (at +24 per mil δ13C) that decaying/eaten, thus not the cause of the CO2 increase, neither of the δ13C decline.

    Moreover, they have monitored the Mount Etna during several years:
    https://www.nature.com/articles/351387a0
    Mount Etna is one of the five most active volcanoes in the world. It emits a lot of CO2 because the African plate is pushed under the Euro-Asian plate and any carbonate sediments are decomposed and its CO2 emitted by the volcano.

    Based on these measurements, all subaerial volcanoes together emit less than 1% of what human currently emit as CO2, and the emissions are near 99% 12CO2, with a 13C/12C ratio higher than the atmosphere. Thus neither in quantity, nor in 13C/12C ratio are volcanoes the cause of the recent CO2 increase in the atmosphere or the δ13C decline...

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