In a 2006 article in JGR, Aslak Grinsted, John Moore, Viejo Pohjola, Tonu Martma and Elisabeth Isaksson study several climate indicators from the Lomonosovfonna ice field in Svalbard, shown below with their caption:
Figure 5. Fifteen-year moving averages of Lomonosovfonna ice core data. (a) Oxygen isotopes, (b) continentality proxy (A), (c) stratigraphic melt indices (SMI), and (d) washout indices (solid line is W_NaMg, and dashed line is W_ClK).
In the oldest part of the core (1130-1200), the washout indices are more than 4 times as high as those seen during the last century, indicating a high degree of runoff. Since 1997 we have performed regular snow pit studies [Virkkunen, 2004], and the very warm 2001 summer resulted in similar loss of ions and washout ratios as the earliest part of the core. This suggests that the Medieval Warm Period [Jones and Mann, 2004] in Svalbard summer conditions were as warm (or warmer) as present-day, consistent with the Northern Hemisphere temperature reconstruction of Moberg et al .
Although the Svalbard ice core record extends back to 1130, a 2009 paper in Climate Dynamics, by Grinsted and 3 of the same authors plus M. Macias Fauria, S. Helama, M. Timonen, and M. Eronen, utilizes the same ice core record to infer winter sea extent, yet omits the distinctively “warm” first 7 decades of the record. It concludes, “The twentieth century sustained the lowest sea ice extent values since A.D. 1200.”
My question for Dr. Grinsted and any of his co-authors who might drop in is, why did the first 7 decades of the core disappear between 2006 and 2009? Is it because they contradict the IPCC/AIT line that there was no MWP to speak of?
Dr. Grinsted does occasionally visit CA, and contributed several helpful comments clarifying his smoothing algorithm on the 7/3 thread The Secret of the Rahmstorf ‘Non-Linear Trend Line’.
BTW, has the Lomonosovfona core data ever been archived? I gathered from Steve’s post that it has not.
I might add that Craig Loehle and myself (see Loehle 2007, Loehle and McCulloch 2008) have reconfirmed the existence of a MWP, using twice as many proxies as Moberg et al. Craig selected the proxies and did the smoothing, while I contributed standard errors to the 2008 correction, showing that the MWP and LIA were both significant relative to the bimillenial average. We did not use Lomonosovfona, but it could be a useful addition to future such studies, if calibrated to temperature and archived.
Update: I would like to thank Dr. Grinsted for responding at length in comment #25 below, as follows:
It is curious that we find that it was warm in Svalbard during the MWP but we do not see a low sea ice extent in our sea ice reconstruction. I would have expected it to be lower even though it does not extend quite as far back. When i was interviewed by the danish press then I pointed this out as the most surprising result. But I do not see a conflict between those two observations.
We had several considerations that led us to restrict the sea ice reconstruction to 1200.
We knew that the oldest data 1100-1200 was influenced by melt to such a degree that ions were being flushed from the ice (Grinsted et al. 2006 and the figure shown on this blog). That made us cautious of whether the isotope data might be influenced by post-depositional processes as well. 1200 seemed a natural choice for the cut-off (see above fig).
The dating-model is expected to perform poorer near the bed. We believe the Lomonosovfonna dating to be quite accurate around 1200, since we have identified a sulphuric peak that we believe to be the 1259 eruption (Moore et al., JGR 2006). However, it is very important for the recontruction procedure that the dating is correct to within 5 years. Otherwise we might try to reconstruct the past ice extent using a lag between ice core and tree ring data that is inconsistent with the one used in the calibration period. The primary reason to do the 5-year smoothing was to make the reconstruction more robust against small dating errors. The dating could still be good prior to 1200AD, however we did not have confidence that the errors would be in an acceptable range for the treatment we were planning and therefore excluded this data. Note that, 1200AD is only 2m above the max depth of the ice core.
The layers gets compressed near the bed and the temporal resolution decreases back in time. For the reconstruction we needed atleast 5 year resolution, because that is what we chose in the calibration period. At 1200AD the d18o temporal resolution is 3-4years per sample. That is OK, but not very good when we want to resample to 5year averages.
@Hu (4): it is also asked why I only showed post-1400 d18O in my JGR 2006 paper. The reason is that E. Isaksson wanted to publish this herself before anybody else could get access to it. That simple. This is also where I will redirect all requests for the isotope data.
He also thoughtfully replies to several questions posed by readers in comments #25, 27, 30, 49, and 59 below.
Update 2: In a subsquent paper with K. Virkkunen et al, Dr. Grinsted and co-authors report on the washout factor from two pits at the summit of Lomonosovfonna that update the original core, which was drilled in 1997. An announcement, entitled “Present day summers in Svalbard are as warm as those during the medieval warm period”, is on Dr. Grinsted’s website, with a link to the full paper. Note that since the horizontal scale is depth in meters rather than inferred calendar date, the present is at the left, while the 12th century is at the right and highly compressed.
It is not clear that this is the same as either of the washout measures shown in figure 5 from Grinsted 2006 above, however, since neither of those has conspicuous up-spikes corresponding to the ones this update shows at around 25 and 32 meters.