Oxygen isotope series are the backbone of deep-time paleoclimate. The canonical 800,000 year comparison of CO2 and temperature uses O18 values from Vostok, Antarctica to estimate temperature. In deep time, O18 values are a real success story: they clearly show changes from the LGM to the Holocene that cohere with glacial moraines.

On its face, Law Dome, which was screened out by Gergis and Karoly, is an extraordinarily important Holocene site as it is, to my knowledge, the highest-accumulation Holocene site yet known, with accumulation almost 10 times greater than the canonical Vostok site. (Accumulation is directly related to resolution: high accumulation enables high resolution.) The graphic below compares glacier thickness for some prominent sites for three periods: 1500-2000, 1000-1500 and 0-1000. its resolution in the past two millennia is nearly double the resolution of the Greenland GRIP and NGRIP sites that have been the topic of intensive study and publication.

Given the high reliance on O18 series in deep time, one would think that paleoclimatologists would be extremely interested in a publication of the Law Dome O18 data and be pressuring Tas van Ommen on this point.

But despite the apparent opportunity offered by Law Dome, there has been virtually no technical publication of a high-resolution O18 or delD isotope series. In 1997, Morgan and van Ommen here published a sketchy diagram based on a core the upper part of which had some technical problems. Although the core offered more resolution than at other locations where annual dating was done, Morgan and van Ommen only showed results back to 1304. They provided this data to Phil Jones, who used it in Jones et al 1998.

The Australians supplemented the long core with two short cores in 1997 and 1999 but did not publish a 1000-year isotope series.

By 2003, they had calculated a 2000-year series at 4-year intervals, but again did not publish this. The unpublished data was again provided to Phil Jones, who used it in Mann and Jones 2003 and plotted it in Jones and Mann 2004. (It showed surprisingly high values at AD1000 and before.) I sought the data from van Ommen as early as 2003; he put me off saying that he planned to publish these results. In 2006, after putting me off again, van Ommen sent me the data, again expressing his intent to publish the results, but, for one reason or another, he didn’t get around to it.

As I’ve mentioned before, the Law Dome series was discussed by IPCC authors in the preparation of AR4. Their Southern Hemisphere graphic showed two proxies: Cook’s Tasmanian and Oroko Swamp NZ tree ring chronologies. As noted a few days ago, these two proxies are the only two proxies in the medieval portion of the Gergis et al network. So despite its claims to novelty, there is nothing new in its medieval portion.

A Climategate email shows that Phil Jones asked about the omission of the Law Dome series from the IPCC illustration in the AR4 First Draft. I asked the same question about the AR4 Second Draft. They realized that the Law Dome graphic had an elevated medieval period and thus, including it in the graphic would – to borrow a phrase from the preparation of AR3 – would “dilute the message” and perhaps provide “fodder to skeptics”. CRU’s Tim Osborn, expert in such matters, proposed that they discuss Law Dome in the running text (thus providing themselves deniability), but not illustrate Law Dome in the graphic (since a picture was worth a thousand words.) CLA Overpeck endorsed Osborn’s sly ‘solution”, sneering at the supposed lack of expertise at even raising the “ambiguity” in the first place:

Hi Tim, Ricardo and friends – your suggestion to leave the figure unchanged makes sense to me. Of course, we need to discuss the Law Dome ambiguity clearly and BRIEFLY in the text, and also in the response to “expert” review comments (sometimes, it is hard to use that term “expert”…). Ricardo, Tim and Keith – can you take care of this please. Nice resolution, thanks.

In making this proposal, Osborn observed (CG2 3092. 2006-07-18)

(2) Goosse et al. showed Deuterium excess [for Law Dome] as an indicator of Southern Ocean SST (rather than local temperature). Goosse et al. also showed a composite of 4 Antarctic ice core records (3 deuterium, 1 O18). Neither of these comes up to the 20th century making plotting on the same scale as observed temperature rather tricky!

I’d followed Law Dome fairly closely but was unaware of any archived deuterium (delD) or deuterium excess data for Law Dome. Re-examining Goosse et al, 2004 (coauthors of which included AR5 CLA Valerie Masson-Delmotte and her husband as well as Law Dome’s Tas van Ommen) in light of this comment, Goosse et al Figure 3b did indeed contain a graph showing deuterium excess from Law Dome as shown below (green):



Original caption to Goosse et al Figure 3. …(b) [Annual mean temperature averaged over the the region 45–60S, 90–130E in an ensemble of 10 simulations (grey) and their mean (red)] and the deuterium excess measured in the Law Dome ice core, 67S–113E (green curve, left vertical axes).

In their text, Goosse et al described the development of the deuterium data for Law Dome as follows:

In addition to some previously published data sets, water stable isotopes (d18O, dD) measured at approximately annual resolution along the DSS (Dome Summit South) ice core drilled on Law Dome (66.46S, 112.48E, 1390 m above sea level) have been used for model-data comparison. The measurement technique and analytical precision are described in Delmotte et al. [2000] and Masson-Delmotte et al. [2003], but we provide here a longer time series. The deuterium excess is a second order isotopic parameter (d = dD 8*d18O) significantly driven by the sea surface temperature at the oceanic moisture source of the precipitation which, for Law Dome, is mainly located in the Indian sector of the Southern Ocean. If no major change occurs in the location of the moisture source, deuterium excess is thus related to change in sea surface temperature there [Delmotte et al., 2000; Masson-Delmotte et al., 2003].

I recently wrote to Tas van Ommen seeking the unarchived delD data. He said that I would have to get it from its originator, Valerie Masson-Delmotte, who had, in connection with Gergis, expressed her hope that AR5 would be based on publicly available data:

We are aware that not all funding agencies or publishers follow a consistent strategy with regard to the public release of data associated with published articles. Regarding your specific concerns, we are confident that the next draft of our chapter will be based on new publications associated with publicly available datasets.

I haven’t heard from her on the Law Dome deuterium series yet.

But aside from my scuffles with IPCC authors over archiving, I wish to express my surprise over the extraordinarily dilatory publication of the near-time Law Dome isotope data. I chided van Ommen about this – van Ommen is pretty reasonable about answering questions. He explained:

Our research focus has been on trace chemistry work, snowfall rates and also for me an excursion into ice sheet work. This will shortly change with papers either just submitted or about to be in coming weeks. These will benefit from improved dating arising from the trace chemistry studies and annual values back to ca. AD170. As soon as any of the publications are accepted we will be archiving the corresponding data set.

On a personal level, I understand that people can’t do everything in the world. But nonetheless, the deep Law Dome hole was drilled between 1987 and 1992. It provides the highest resolution ice core for the two-millennium period. And remains unpublished. Amazing.

Postscript: Here is a reminder of what the 2003 O18 version looked like. An annual version for two millennia was provided to Gergis (who screened it out.) delD and O18 are closely related and presumably the unarchived del D series will look somewhat similar.



Update June 13: In a 1985 article on an earlier core (also showing elevated MWP values), Morgan commented on potential aliasing of the data by changes in accumulation (and thus elevation.) Slight and feasible increases in elevation could cause the observed secular decline in d18O values. An increase in accumulation would, of course, be of interest for potential sea level changes.

The present day d18O versus elevation relation for the Law Dome is d18O = -0.0054 E(m) – 15.3 (Morgan, 1980) so a 0.1%% aliasing, which is just significant in the d18O profile requires an elevation change of 19 m. If such changes are climatically induced, their effect is mainly to reduce the amplitude of the d18O changes, because an increase in temperature gives increased accumulation which, after some time produces a higher ice cap surface with correspondingly reduced surface temperature.

Update June 13: Deuterium excess data for Law Dome from 890-1841 was archived at Hugues Goosse’s this morning (http://www.elic.ucl.ac.be/repomodx/users/hgs/Law_Dome_deutxs.dat). Here’s what it looked like. The shift around AD1000 in this series is quite pronounced. The Goosse et al 2004 graphic cuts off at AD1000; looking closely it shows a downspike at the start, but it’s a much more prominent feature in the version shown below.

Valerie Masson-Delmotte comments:

The seasonal cycle of deuterium excess was investigated in :

Delmotte, M., Masson, V., Jouzel, J. and Morgan, V., 2000. A seasonal deuterium excess signal at Law Dome, coastal eastern Antarctica: a southern ocean signature. J. Geophys. Res., 105(D6): 7187-7197. and the inter-annual variations for the last decades in :

Masson-Delmotte, V., Delmotte, M., Morgan, V., Etheridge, D., Ommen, T.v., Tartarin, S. and Hoffmann, G., 2003. Recent southern Indian Ocean climate variability inferred from a Law Dome ice core: new insights for the interpretation of coastal Antarctic isotopic records. Clim. Dyn., 21: 151-166. A number of issues are related to the quantitative interpretation of water stable isotopes in relationship with precipitation intermittency and moisture sources, in addition to the direct impact of condensation temperature on distillation.

I’ve asked them to also archive the underlying deuterium series. Also why there are no values after 1841.



