TN05-17 is by far the most influential Southern Hemisphere core in Marcott et al 2013- it’s Marcott’s YAD061, so to speak. Its influence is much enhanced by the interaction of short-segment centering in the mid-Holocene and non-robustness in the modern period. Marcott’s SHX reconstruction becomes worthless well before the 20th century, a point that they have not yet admitted, let alone volunteered.
Marcott’s TN05-17 series is a bit of an odd duck within his dataset. It is the only ocean core in which the temperature is estimated by Modern Analogue Technique on diatoms; only one other ocean core uses Modern Antalogue Technique (MD79-257). The significance of this core was spotted early on by ^.
TN05-17 is plotted below. Rather unusually among Holocene proxies, its mid-Holocene values are very cold. Centering on 4500-5500 BP in Marcott style results in this proxy having very high anomalies in the modern period: closing at a Yamalian apparent anomaly of over 4 deg C.
Figure 1. TN05-17.
In the most recent portion of the Marcott SHX, there are 5 or fewer series, as compared to 12 in the mid-Holocene. Had the data been centered on the most recent millennium and extended back (e.g. Hansen’s reference station method is a lowbrow method), then there would have been an extreme negative contribution from TN05-17 in the mid-Holocene, but its contribution to the average would have been less (divided by 12, instead of 4). As shown below, TN05-17 pretty much by itself contributes the positive recent values of the SHX reconstruction. It’s closing anomaly (basis 4500-5500 BP) is 4.01 deg. There are 4 contributing series – so the contribution of TN05-17 to the SHX composite in 1940 is 4.01/4, more than the actual SHX value. The entire increase in the Marcott SHX from at least 1800AD on arises from increased influence of TN05-17 – the phenomenon pointed out in my post on upticks.
Figure 2. Contribution of TN05-17 to the Marcott SHX reconstruction.
Given the overwhelming importance of this proxy, one would like to know a little more about it. The next graphic compares TN05-17 to two other SHX proxies, also MAT proxies but from small lakes in southern New Zealand. The inconsistency of the proxies is evident. The New Zealand paleolimnological proxies have nothing resembling the mid-Holocene “cold period” that characterizes TN05-17. One thing that this graphic shows for sure: the residuals of these proxies from the “true” temperature history as translated to the respective sites do not remotely resemble a low-order AR1 process. To properly model the error distribution, one has to have an error model that permits excursions for millennia – not at all easy to specify.
Figure 3. Three SHX Modern Analogue Technique Proxies
It appears highly probable that there is some confounding influence on TN05-17. TN05-17 was cored in the Atlantic sector of the Southern Ocean south of Africa. As shown in the graphic below, it is located in very large scale “sediment drifts”.
Figure 4. Location map of TN05-17 (shown as red dot.)
Nielsen et al 2004 observed that the alkenone temperatures of the most recent samples are several degrees higher than ocean temperatures in the area. They speculated that some of the coretop might be missing – not particularly reassuring when this proxy is the most important contributor not just to 20th century SHX Marcott warming but 19th century SHX Marcott warming. There is occasional discussion in specialist literature of circumstances in which alkenone temperatures are warmer than local ocean temperatures e.g. Ruhlemann et al taking the alkenones from the warmer location in which they formed to the colder place where they settled:
We suggest that the southern samples are biased by suspended organic detritus originating from the cold subpolar waters of the northward flowing Malvinas Current, whereas the northern samples carry an UK’37 signal of tropical/
subtropical origin, transported southward with the Brazil Current. On the basis of surface ocean transport pathways and velocities simulated with the large-scale geostrophic (LSG) ocean general circulation model, we identify areas of the world ocean where alkenone temperatures are potentially biased to higher or lower values due to long particle residence times and lateral advection by surface currents.
The area studied by Ruhlemann et al was in the western South Atlantic between 30 and S. Could something similar be going in the eastern South Atlantic in the area of TN05-17 (50S, 6E) – seems entirely possible to me. There is convincing evidence that there have been secular changes in the Agulhas currents over the Holocene. The TN07-17 history certainly suggests secular changes to me: it looks like ocean currents have changed in this sector over the Holocene, such that alkenone drift (along the lines of the South American alkenone drift) has contributed to the warm values in the early Holocene and later Holocene, while colder currents were present in the mid-Holocene.
Whatever is right or wrong about Marcott et al, merely from a perspective of craftsmanship, it is not particularly reassuring that the main (Yad061 even) contribution to modern SHX warming in the Marcott reconstruction appears to arise from a “cold” mid-Holocene interval at TN05-17, translated into modern warming through short-segment mid-Holocene centering and modern proxy dropout.
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“…closing at a Yamalian apparent anomaly of over 4 deg C.
When one considers that the alkenone-derived SST change from the Eemian to the LGM was around 4-5C, one begins to wonder whether any of Marcott’s peer reviewers knew anything at all about alkenone proxies, or even paleo-SST for that matter.
F. G. Prahl, of OSU, wrote the book on alkenone paleotemperature calibration, so, one would imagine Marcott of OSU had access to world class help.
Your point about currents does not give me great confidence in the “ocean core” methods. How well is the history of ocean currents known?
Diatoms would be much less prone to advection than alkenones. Firstly, they are much larger and heavier; secondly they are a huge production of diatoms in the southern ocean so the advected signal would be swamped.
richard, what would account for a large discrepancy between modern SST and core-estimated SST? DO you have any theories or explanations for the huge downward excursion in TB-5-17 in the mid-Holocene – an excursion that one doesnt see in other proxies?
Alkenone molecules are highly lipophilic hydrocarbons and are not particularly soluble in water. Free molecules would almost certainly adsorb to clay and other sedimentary particles. They would advect along with current-driven sedimentary particles.
Alkenones are also subject to aerobic bacterial modification while still associated with E. huxleyi, so the recovered “signal” might not be pristine. Here’s a bit of the abstract from a 2008 paper from Jean-Francois Rotani, et al., “Degradation of alkenones by aerobic heterotrophic bacteria: Selective or not?
“Four bacterial communities were isolated from Emiliania huxleyi strain TWP1 cultures before and after the algal cells had been treated with different antibiotics. Incubation of E. huxleyi with these bacterial communities resulted in dramatically different extents of alkenone degradation, ranging from effectively none to extensive. Selective degradation of the more unsaturated alkenones was observed in experiments using the total bacterial community and one of the communities isolated from antibiotic-treated algal cells. The observed increases in U37K are equivalent to a +2 °C and +3.3 °C change in the inferred temperature. Our results clearly show that intense aerobic microbial degradative processes have the potential to introduce a significant ‘warm’ bias in palaeotemperature reconstruction and could explain apparent anomalies in palaeotemperatures inferred from alkenone distributions in strongly oxidizing sedimentary environments. The results show that aerobic bacteria capable of selectively degrading alkenones are not limited to particular environments such as microbial mats and can be actually associated with living E. huxleyi cells.”
After anaerobic burial in the sedimentary column, alkenones are apparently quite stable and are either not, or only very slowly, modified by anaerobic bacteria.
However, laboratory methods lead to another source of uncertainty. From a review of alkenone modification in 2000 by Joan O. Grimalt, et al.: “During repeated gas chromatographic measurements, major deviations of U37K′ determinations have been observed as consequence of capillary column adsorption effects. These effects shift the U37K′ indices toward higher values (warmer temperatures) due to stronger adsorption of the C37:3 compound. The deviations are significant when the amount of C37 alkenones injected onto the capillary column is low. This instrumental limitation defines a threshold of minimal sample concentration below which U37K′ determinations are not reliable.”
How many paleo-temperature reconstructionists check the analytical method behind the proxy they’ve chosen?
Pat Frank, thank you for finding these interesting references. I speculated yesterday on the alkenone divergence off Iceland thread that the recent decline in estimated alkenone temperatures that seemed to be prevalent in most cores was a result of degradation. It’s interesting to note thatthe magnitude of the temperature shifts observed in this paper are i) of the same order as observed in core tops and ii) go in the same direction as observed in core tops.
Still might not be the explanation for what is happening here but it backs the ideas that both you and I have that we need a much better physical understanding of the response and behaviour of proxies. Mere calibrations by correlating observed U37k ratios with SST’s at core sites might well throw up a good correlation but tells us nothing about the processes and reliability of such proxies.
Paul, hope you’re still reading here. You’re in an excellent position to write a critical review of the physical accuracy of the standard temperature proxies, notably dO-18 and the alkenones, but also the metal-based proxies.
It would require doing some error analysis on the published laboratory calibration experiments, but that should be straight-forward. Such a paper would be a shot across the bow for all these proxy studies that ignore the physical limits of accuracy.
You have the professional standing to make everyone pay attention, Paul. The case could be made that mere statistical combinatorial methods of combining proxies produce physically meaningless results. Error bars that do not include the physical accuracy of the method are also meaningless. Subsequent papers would be forced to address your concerns.
Pat, I think I missed your excellent WUWT article last year. We’re now 60+ years on from the original Urey, Epstein, Lowenstam and McRea work on oxygen isotope partitioning between water and carbonate minerals. In many respects the view is still relatively opaque. Recent data suggest that the published ‘equilibrium’ fractionations may actually represent disequilibrium processes. In my lab we’re starting a new programme to calibrate several isotope thermometers including oxygen isotope fractionation between water and carbonate minerals, and the new ‘clumped isotope’ (D47) thermometer.
I like your suggestion of a review article that critically evaluates the different proxies. Such a paper would be timely, but also fits with ourongoing work on temperature calibration. Could you either email me (paul underscore f underscore dennis at fast mail.fm), to give me your email address so that we could exchange some ideas.
From my point of view a key issue has been the rapid development of automated systems and ‘black box’ instruments for stable isotope analysis. The result is the generation of large numbers of data without proper consideration of errors.
Re: Paul Dennis (Apr 11 02:34),
I’m only the “peanut gallery” but may I urge Paul Dennis and others to consider purusing Pat Frank’s suggestions about more rigorous error analysis for various types of proxies. The glaring weaknesses of many proxy studies seem to stem in part from too many untested assumptions and lack of rigor in evaluating the physical basis of proxies. It would be great to see some independent scientific analysis of such aspects of the multi-proxy papers.
I’ve sent you an email, Paul, and am looking forward to the conversation.
Re: Pat Frank (Apr 10 21:58),
What I see here is that there’s published literature on further physical uncertainties, that’s being (studiously?) ignored.
Combine that with the allergic reaction to uncertainty demonstrated by various scientists (and team-apologist) posters here and elsewhere, and we obtain a very skewed view of LOSU (Level Of Scientific Uncertainty).
In this era of google search/scholar and crowd-sourced Wikis… I’m getting hungry for an ongoing community process of indexing important facts related to the (physical, methodological, etc) factors that need to be taken into account when using any particular physical data source or math/stats methodology in science.
“Nielsen et al 2004 observed that the alkenone”
You have a glitch here. Nielsen et al 2004 does not mention alkenones – just diatoms, so your discussion that follows is only partially relevant.
TN05-17 is near the polar front. Small changes in the position of the front would give a large change in temperature at the site.
Dr. Telford:
Are you saying the TN05-17 mid-Holocene declines are not due to depositional or biogeochemical factors? The range of the departure is pretty close to the max error range found by Prahl (see below). Correlation is not causation, but it makes one wonder if this is a simple “false positive” sample. Perhaps the false positive factors have been examined and determined to be insignificant. Can you shed any light on this?
More generally, for something subject to many many different signal degradation factors through space and time, if I was in this field, I would be looking at all of these degradation factors and try and figure out which cores provided the most representative, unpolluted and undisturbed alkenone signal rather that hoping that all manner, type and temporal variability of signal degradation would somehow cancel out using ad hoc statistics and the real signal would shine through.
I might sound like a jerk, but really appreciate your participation here Dr Telford and hopefully you can educate some of us dilettantes who are willing to learn.
Nielsen et al 2004 is not an alkenone record: issues pertaining to alkenones are simply not relevant. Nielsen et al 2004 use the diatom assemblages to reconstruct temperature using a method called the Modern Analogue Technique.
Thanks Dr. Telford: I didn’t connect the dots that Nielson et al = the TN05-17 core. What a dummy I am. So you are saying that since diatoms are denser, they are less likely to scatter. So this proxy may be more related to temperature fluctuations from shifting in ocean current patterns due to the proximity to the polar front?
Does this location near polar front location make this proxy a poor choice for use in global temperature reconstructions?
Thanks for your help!
Possible cause from down under or CA?
This comment provides input to previous posts regarding alkenone divergence. Have any of the core sample datings considered that the upper 10 to 20 centimeters of sediment are continuously worked over by benthic organisms? Biological activity (bioturbation) physically averages out the upper layer of sediment as explained for example in this overview:
“What is bioturbation? The need for a precise definition for fauna in aquatic sciences”
Click to access m446p285.pdf
This reference from Oregon State University describes the impact of bioturbation on dating:
“Long-Chain Alkenones – An Eyepiece to Past Oceanographic Conditions”
http://chemoc.coas.oregonstate.edu/~fprahl/alkdesc.html
“Organic matter produced in surface ocean waters illuminated by sunlight (the “euphotic zone”) provides the fuel for the food chain (zooplankton, fishes and mammals including humans). Very little of this primary production goes to waste in the ocean. The vast majority (~99%) is eaten and respired somewhere within the water column; the small remainder settles to the seafloor packaged within particles such as fecal pellets and marine snow. Continuation of this particle rain over time yields a sediment record. Under ideal conditions, the sediment record can be layered (“varved”), each varve representing a discrete time in the past. More often, however, the surfacemost part of the deposit is stirred biologically (bioturbation), smearing the time resolution of the sediment record.”
Other examples of bioturbation affecting age dating:
“Asynchronous alkenone and foraminifera records from the Benguela Upwelling System”
http://nosams.mblwhoilibrary.org/works/1127
“Interestingly, the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples. Such age differences may be the result of different processes: Bioturbation associated with grain size effects, lateral advection of (recycled) material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes.”
“Alkenones as paleoceanographic proxies”
Click to access Sachs-Alkenones_as_Paleoceanographic_Proxies-G300.pdf
“Another artifact of bioturbation stems from the fact that the depth of mixing is dependent on particle size [Ruddiman and Glover, 1972; Thomson el al., 1988; Wheatcroft, 1992; Wheatcrofi and Jumars, 1987]. Small particles are preferentially ingested by deposit feeders and mixed downward, in effect biologically “pumping” coarser panicles toward the surface [McCave, 1988, 1995]. If the size fraction of alkenone-enriched particles differs from that of foraminifera, there is the potential for climate proxies to become decoupled or offset in the depth (and time) domain. This process has been cited as a possible cause for the deep penetration of bomb-derived radionuclides in North Pacific sediments [Druffel et al., 1984] and for radiocarbon age differences between forams and bulk carbonate in northeastern Atlantic sediments [Thomson et al., 1995] and between forams and nannofossils (coccoliths) in South Atlantic sediments [Paull e1 al., 1991].”
Another couple of hours of reading ahead of me, but this may be yet another case on CA of the comment being even more informative than the original article. Well done.
Any research on the possible effects of microorganisms on bioturbation, or sediment composition in general?
W^3
“it is not particularly reassuring that the main (Yad061 even) contribution to modern SHX warming in the Marcott reconstruction appears to arise from a “cold” mid-Holocene interval at TN05-17, translated into modern warming through short-segment mid-Holocene centering and modern proxy dropout. “
TN05-17 is influential in SHX because it is one of few continuing to present. But why is it more or less influential than those others? The fact that recent values are high would be significant if TN05-17 dropped out, but it didn’t. It has a recent uptrend, but that would be reflected in the recon regardless of the anomaly base. Its dating has undergone almost no adjustment.
You might say that its positive value influenced other dropout effects. But this just reflects its growing influence as the number shrinks.
It certainly has behaviour that is worth commenting on. But I can’t see that its effect is inappropriately amplified by the analysis.
Marcott et al made no special claims about 19C warming. In fact, they said
“The results suggest that at longer periods, more variability is preserved, with essentially no variability preserved at periods shorter than 300 years, ~50% preserved at 1000-year periods, and nearly all of the variability preserved for periods longer than 2000 years (figs. S17 and S18).”
This is even more true of sub-regions like SHX.
Nick,
I already pointed out to you on March 27 in a comment on your blog that TNO5-17 is the cause of the uptick in the Southern Hemisphere.( see also http://clivebest.com/blog/?p=4790 )
“I think the spike can be understood by interpolating just one Proxy TNO5-17. There are only 2 recorded measurements post 1900 for this proxy.
Date Anomaly deg.C
1904 2.3
1950 4.5
Interpolation to a 20 year spacing then gives us.
1900 2.0
1920 3.1
1940 4.0
1960 5.0
a linearly increasing spike !”
No amount of Monte-Carlo simulation or infilling of data by linear interpolation can alter this trend.
The standard deviation on measurements for this proxy between 5500 – 4500 ybp is 0.7C. The statistical error on the anomaly is 0.8C.
So the uptick in this one proxy is itself not statistically significant.
Consider the potential for variance loss that this poses for the temperature calibration step and propagation of that bias into a reconstruction like Marcott’s.
This is Steve’s version of death by a thousand cuts. It has got to be painful. At the same time it sheds enormous and embarrassing light on the mindset of some of those who put such proxies studies together.
So then… what can be “publishable” from all this work?
I don’t think you’re going to get away with dictating into the literature that alkenones (and tree rings) can not be reliably used as proxies in temperature reconstruction.
Since Steve finds other proxies that weren’t used in Marcott but yet seem proximal (and/or even more informative)– is the answer to come up with a new reconstruction? Other reconstructions can certainly get published, with the side-advantage of getting words into the record regarding methodology (just like Marcott et al and other reconstructions). Naturally you’d get peer reviewed by purveyors of other reconstructions.
What can be done with this information? New error-bar/uncertainty understanding? New work put into the record regarding the challenges of the validation of proxies during overlap periods (eg., Marcott vs. Mann vs. Instrument record, etc.)?
I think it was Mr. Pete on another thread who laid out the procedural steps for a more rigorous and vigorous approach to proxy studies. Paradoxically these summary type studies may be poor candidates for publication in high visibility journals such as Science and Nature: They seem to be building castles on sand.
“get your money for nothing
and your ‘sticks for free”
Apologies to M. Knopfler
@Neil Jordan – At one time, all the layers were once the upper layer. So the smoothing due to bioturbation would affect the entire core.
That’s right. And bioturbation depth (say 10 cm) divided by deposition rate (say cm per century) gives a rough estimate of the number of years of averaging beneath any depth in the core.
Actually, it seems it would be worse than that. If you add 1 cm to a 10 cm deposit, then the 1 + 9 cm get mixed. Some of the 9 came from what is now the 11 cm deep part. So, the averaging effect would be > just the 10 cm.
Between this and the potential ocean current meander problem, this sort of proxy is beginning to look worse even than tree rings.
Re: jim2 (Apr 10 21:49),
Is it possible that meandering ocean currents could affect the bioturbation processes within that 10cm depth, doing so in ways that add other sources of variation which might affect the temperature proxy indicators contained within the sediments — sources of variation that were not consistently applied to the bioturbation processes that were operative over the full period of time represented by the core?
There is a link between both alkenone/phytoplankton and tree-ring proxies used for temperature reconstructions, they both use photosynthesis for growth. To trigger the photosynthesis process needs CO2, heat, photons (light) and water.
When comparing 5114 days, for a UK location, of maximum daily temperature (Ix) and a photosynthesis index (P-Index)I found some interesting results. The P-Index is a combination of air (gases), heat, light and water.
Over the whole period there was a correlation between Tx and P-Index 0.69
Days % Explanation
3392 66.3 PI days when Photosynthesis Does Not Occur
1628 31.8 PI days when Photosynthesis Will Occur
94 1.8 Gas/Heat/Water Stress Days
5114 100.0 Total Days
4444 86.9 Tx days when Photosynthesis Could Occur (>6.9 DegC/PI)
This may cause some doubt as to the reliability of using photosynthesising organisms as proxies for historic temperature reconstructions.
If anyone would like these data, I’ll email them to Steve
I can’t rely on the SHX after 1250 since the number of proxies drops below 10, regardless of whether or not I “like” the results. I need more proxies that extend into the last millenium so that the results are not overly influenced by a single proxy.
It’s only an impression, but it looks a lot like Upside Down TN05-17 to me…
A South Sea Bubble.
===========
It seems that there is enough here to do a corrective journal article, as with the corrective to Stieg et al. Let’s get Nic Lewis and Steve and others on the job, pronto! An article will have far more influence than Steve’s blog, no matter how accurate Steve is.
Another way of saying this is that it’s Yanomalous.
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