It’s clear there are a lot of confounding factors in each case; tree rings and calcerous plankton both. Honestly, it will take a real professional, cognizant of all the subtlties, to sort it out and decide whether an isotope effect can produce a valid thermometer.

Pat, Emiliania huxleyi, one of the abundant coccolithophores (phytoplankton with a calcite skeleton), may be a good candidate for d13C variation search. Ocean sediments are already used as (ocean) surface temperature proxy, see J. Eiràƒ⬫sson ea., where they used several types of proxy measurements. Interesting is that they detected several solar cycles and a (2 K) warmer MWP vs. a colder LIA in the near Icelandic sediment…

The relative slower change of d13C of upper ocean waters vs. air may be a matter of CO2 storage capacity of shallow waters vs. the atmosphere in equilibrium. This may be about 1.25:1 (something that is alluded too in carbon cycle diagrams).
Organic carbon in phytoplankton is preferentially build with 12C (as one of the oldest lifeforms, probably C3 cycle? Paul may give some better explanation here!), thus during build-up of the organics, the surrounding water will get enriched in 13C vs. the atmosphere. The shells are build with a direct (non-organic) chemical reaction, and reflect the 13C ratio of the surrounding water (at the time of formation, which varies with the seasons, and may be influenced by the inner organic buildup…).

Thus even in the pre-industrial more or less dynamic equilibrium between air and upper ocean waters, the d13C in water is always higher than in air. Deep ocean water at the other side is richer in 13C (around 0 pro mil) than air, but poorer than the upper ocean layer. Any change in upwelling of the oceans (as good as any change in more or less downwelling of cold CO2-rich waters at the North Atlantic sinks) will have its influence on the equilibrium…

Gruber, Keeling and Bates made a comprehensive overview of the difficulties involved in calculating the variability of North Atlantic carbon sinks over the years. The supplemental material is particularly interesting, and the equation includes a term for changes in mixed upper ocean volume over the seasons.

Pat, Emiliania huxleyi, one of the abundant coccolithophores (phytoplankton with a calcite skeleton), may be a good candidate for d13C variation search. Ocean sediments are already used as (ocean) surface temperature proxy, see J. Eiràƒ⬫sson ea., where they used several types of proxy measurements. Interesting is that they detected several solar cycles and a (2 K) warmer MWP vs. a colder LIA in the near Icelandic sediment…

The relative slower change of d13C of upper ocean waters vs. air may be a matter of CO2 storage capacity of shallow waters vs. the atmosphere in equilibrium. This may be about 1.25:1 (something that is alluded too in carbon cycle diagrams).
Organic carbon in phytoplankton is preferentially build with 12C (as one of the oldest lifeforms, probably C3 cycle? Paul may give some better explanation here!), thus during build-up of the organics, the surrounding water will get enriched in 13C vs. the atmosphere. The shells are build with a direct (non-organic) chemical reaction, and reflect the 13C ratio of the surrounding water (at the time of formation, which varies with the seasons, and may be influenced by the inner organic buildup…).

Thus even in the pre-industrial more or less dynamic equilibrium between air and upper ocean waters, the d13C in water is always higher than in air. Deep ocean water at the other side is richer in 13C (around 0 pro mil) than air, but poorer than the upper ocean layer. Any change in upwelling of the oceans (as good as any change in more or less downwelling of cold CO2-rich waters at the North Atlantic sinks) will have its influence on the equilibrium…

Gruber, Keeling and Bates made a comprehensive overview of the difficulties involved in calculating the variability of North Atlantic carbon sinks over the years. The supplemental material is particularly interesting, and the equation includes a term for changes in mixed upper ocean volume over the seasons.

Thinking about the problem and the various difficulties — shallow fresh water getting infusions of old carbonate or decaying matter, etc. — it occurred to me to wonder whether there is a calcerous oceanic surface-water diatom one could use. If there was, then one could baseline its 12C/13C response versus the modern atmospheric values so as to get a calibration with respect to its metabolic isotope effect. Perhaps one could extend this across a century or so, using the most reliable 12C/13C atmospheric ratios, to see if the metabolic effect is reproducible and stable. One would then look for exactly that species of diatom in sedimentary benthic drill cores and do the 12C/13C ratio. So long as the calcerous morphology was unchanged in retro-time, one could reasonably argue for species identity and the same metabolic isotopic frationation as the modern species.

I understand from previous discussions here that there may be a problem with carbonate exchange over time in sedimentary diatoms. That would, of course, progressively skew the pristine 12C/13C diatomaceous carbonate ratio. But I wonder whether one could experimentally account for that, by adapting a method from K/Ar dating. That is, one could argue that any carbonate exchange process would most strongly affect the surface layers of the diatomaceous carbonate, and this exchange would progressively attenuate deeper into the skeleton.

So, suppose one baked the sample with a progressive series of temperatures, taking advantage of the thermal reaction: CaCO3 —-(heat)—-> CO2 + CaO. Each pulse of CO2, coming from deeper in the calcerous skeleton, would be swept into the GC-MS and the 12C/13C ratio measured. At some point, if a pristine layer is reached, the data would show a progressively sloped plot, followed by a plateau. The plateau should show the original 12C/13C ratio.

Would that work, Paul? If it did, it also seems possible that the same diatom could be used to reconstruct ancient SST’s using the identical kinetic isotope method we’ve discussed above for tree rings. That is, one could derive a deltaEa for the modern diatom in the same way as might be derived for a tree species. It could be tested against slightly older diatoms for which the SSTs and atmospheric 12C/!3C ratios were known. Knowing the deltaEa derived from modern diatoms, would could apply it to the measured pristine 12C/13C ratio of ancient conspecific diatoms and back-calculate the ancient ambient sea surface temperature.

Thanks for the job-offer by the way, even in jest. As you deduced I am indeed, like you, an experimental scientist, happily employed at SLAC. If you ever need to speciate sulfur — sulphur, to you — in complex materials, let me know. I had the pleasure of working on wood from the 17th century Swedish ship “Vasa” awhile back.

#142 — Thanks for the better graph, Ferdinand, it’s much easier to read. I wonder, do you think the 80% scaling is due to a metabolic isotope effect of the sponge, that depletes 13C in its skeleton? I can’t think, just now, why the atmospheric 12C/13C ratio would change much because of dissolution in water.

It looks like they have used the shallow water sponge data to make a base line. The problem with the air data is that they needed to scale down the air d13C scale (as the d13C change in water is about 80% of the change in air) to make air/water changes comparable, but that the dd13Cwater/dd13Cair is not constant, thus the 1400-1850 AD avarage for air indeed may be somewhat higher.

You are right about the relative small pre-industrial changes. That should be the result of some 1 K difference in temperature between MWP and LIA (although in this case the MWP is not covered). But, indeed that doesn’t say much about the changes in d13C one will find in tree rings covering the MWP-LIA period. Only that the influence of changing d13C levels in the pre-industrial period were much smaller than thereafter, and will have less influence on the temperature “calculation”…

I have posted a new graph with a better resolution at the previous link. It seems that the previous code to present graphics on the blog doesn’t work anymore (John A!) and the reply box shows some strange behaviour (text dissapears at the extended right side of the box) in IE…

Mark, I think all these have some potential but one needs to be careful. If there is any organic material present then even small amounts of decay and oxidation will produce CO2.

It’s an interesting thought Pat. Are you an experimentalist and analyst by any chance. You have a good grasp of appropriate techniques. You wouldn’t like a job in my lab would you!? I think there is a potential problem with magma derived CO2. All magmas contain varying amounts of CO2, though much of this is outgassed at the time of the eruption. Some would potentially be included in gas vesicles and would interfere with the atmospheric signal. There are quite a large number of studies looking at gas released from crushed basalts and other rocks and minerals. Most of these are aimed at understanding the processes that occur in magma chambers etc.

With respect to minerals I remember that Yapp and co-workers had carried out some interesting experiments on goethite (an iron hydroxide mineral) that is formed as a weathering product. On heating the goethite released CO2 with distinctive isotope signatures. I don’t believe that the compositions were ever related to atmospheric compositions and I’m not sure if this idea was ever developed very far.

From time to time I’ve put my mind towards the problem of accurately measuring pre-industrial atmospheric compositions and now the debate here has spurred my interest again. There is a rich heritage of great scientists including Lavoisier, Priestley and others who have measured the composition of air. One wonders if any of their flasks still exist that have remained sealed. I once asked the Cavendish Laboratory in Cambridge if they had any. Othe rplaces might be the Royal Institute.

In all seriousness such measurements would only provide a patchy record. What is required is an archive that has global distribution and a potentially good time resolution and certainly better than a decade.