Kaufman and paleo peer reviewers ought to be aware that the recent portion of varve data can be contaminated by modern agriculture, as this was a contentious issue in relation to Mann et al 2008 (Upside Down Mann) and Kaufman et al 2009. Nonetheless, Kaufman et al 2013 (PAGES), despite dozens of coauthors and peer review at the two most prominent science journals, committed precisely the same mistake as his earlier article, though the location of the contaminated data is different.
The contaminated series is readily identified as an outlier through a simple inspection of the data. The evidence of contamination by recent agriculture in the specialist articles is completely unequivocal. This sort of mistake shouldn’t be that hard to spot even for real climate scientists.
Here is a plot of the last nine (of 22) Arctic sediment series. One of these series (top left – Igaliku) has the classic shape of the contaminated Finnish sediment series (often described as upside down Tiljander). Any proper data analyst plots data and inspects outliers, especially ones that overly contribute to the expected answer. The Igaliku series demands further inspection under routine data analysis.
The Igaliku series is plotted separately below. It is also available at a NOAA archive here , which actually contains one additional recent value plotted in red. The NOAA archive contains many other measurements: it is unclear why Kaufman selected pollen accumulation rate out of all the available measurements.
The resolution of the data set is only 56 years (coarser than the stated minimum of 50 years) and only has three values in the 20th century. The value in 1916 was lower than late medieval values, but had dramatically surged in the late part of the 20th century.
Igaliku is in Greenland and was the location of the Norse settlement founded by Erik the Red and is of archaeological interest. Sediment series from Lake Igaliku have been described in three specialist publications in 2012:
Massa et al, 2012. Journal of Paleolimnology, A multiproxy evaluation of Holocene environmental change from Lake Igaliku, South Greenland.
(Not presently online). (Update: online here h/t Mosher. I’ve added a paragraph from this text referring to pollen accumulation.)
Massa et al 2012. QSR. A 2500 year record of natural and anthropogenic soil erosion in South Greenland. Online here.
Perren et al 2012, 2012. Holocene. A paleoecological perspective on 1450 years of human impacts from a lake in southern Greenland. Online here.
The three articles clearly demonstrate that the sediments are contaminated as climate proxies.
Igaliku has been re-settled in the 20th century and modern agricultural practices have been introduced. The specialist publications make it overwhelmingly clear that modern agriculture has resulted in dramatic changes to the sediments, rendering the recent portion of the Igaliku series unusable as a climate proxy. Here are some quotes from the original article.
The modern community consists of 60 permanent inhabitants and was founded in the late 1700s. Agricultural practices resumed in the 1920s, at the same time that the climate of southern Greenland reached its recent maximum (Box et al., 2009). Current sheep farming in the catchment is limited to one farm, established in the early 1960s, which has a barn for wintering sheep and summer hay production on a 30 ha field. A small ditch currently drains effluent from the barn into the nearby lake. The farm currently deploys 750-900 kg N fertilizer per year within the lake catchment to boost yields for winter fodder (Mikki Egede, personal communication, 2011)
A multiproxy sedimentary record from Lake Igaliku in southern Greenland documents 1450 years of human impacts on the landscape. Diatoms, scaled chrysophytes, and C and N geochemistry show perturbations consistent with recent agricultural activities (post- ad 1980), superimposed upon long-term environmental variability. While the response to Norse agriculture (~ ad 986-1450) is weak, the biological response to the last 30 years of modern sheep farming is marked, with drastic changes in diatom taxa, d 13 C and d 15 N isotopic ratios, and a sharp increase in scaled chrysophytes. Indeed, current conditions in the lake during the last 30 years are unprecedented in the context of the last 1450 years. The dominant driver for recent changes is likely an intensification of agricultural practices combined with warming summer temperatures. W
The PCA of diatom results show two major features: a major shift in lake ecology ~ ad 1980 as registered in the PCA axis 1… the rise in d15N in Igaliku is likely a result of the addition of fertilizers from manure and industrial sources, but some component of internal utilization of N, such as enhanced sediment denitrification, cannot be ruled out.
However, beginning in 1976, the method of farming shifted towards fodder production and higher yields at slaughter which introduced fertilizers
(250-300 kg/ha per yr) and effluent from winter sheep stables into the local landscape and lake (Figure 7: agricultural phase II; Greenland Agriculture Advisory Board, 2009). After 1976, sediments from Igaliku show a rise in planktonic diatoms ( Cyclotella stelligera, Fragilaria tenera ), as well as chrysophyte scales, d15N, and N, reflecting increased nutrient additions and the beginning of industrialized agriculture.
The digging of drainage ditches for hayﬁelds caused a dramatic increase in MAR, which reached unprecedented values. The use of nitrogen fertilizers on theseﬁelds (200–250 kg ha -1 yr -1of N, Miki Egede pers.commun.) have outpaced the natural buffering capacity of Lake Igaliku, resulting in a sharp rise in the mesotrophic diatom,
This is precisely the same sort of contamination that affected the Korttajarvi sediments in Finland – for which, Kaufman, Mann and others were rightly criticized at Climate Audit. Kaufman conceded that the prior criticism was justified by issuing a corrigendum to Kaufman et al 2009 (but conspicuously failed to acknowledge Climate Audit or myself by name). It’s ludicrous that Kaufman has made an identical error with a different site. And that peer review at major journal was unequal to the identification of an error that Kaufman’s made in the past.
Now it is not evident to me that Kaufman’s varvology lends itself to multiproxy sausage-makers in any event. Varve compaction was not addressed in Kaufman et al 2013 and has the potential for a very serious bias. Nor is there any direct physical connection between temperature and varve thicknesses. The traditional interpretation of varves requires presence of a nearby ice cap and thin varves have been interpreted as evidence of warmth and thick varves as evidence of cold (Miller et al 2012) – the exact opposite of Kaufman. Until such issues are resolved, varve thickness data is unusable for temperature reconstructions that are destined for policy-maker consumption.
The network was unusable in the first place. However, the unusability is made much more evident when the authors and peer reviewers are once again unequal to the small task of separating out contaminated data.
Does this sort of error “matter” to the reconstruction? It’s hard to say.
It did in the case of the no-dendro reconstruction of Mann et al 2008, though it was never formally retracted. In that case, Mann toughed it out and continued to use the contaminated no-dendro reconstruction of Mann et al 2008 even after conceding it did not validate prior to AD1500 without the contaminated Tiljander data: see 2012 RC here; also cited in the EPA response to the Petition for Reconsideration). On the other hand, the Kaufman et al 2009 reconstruction was able to survive the correction of contaminated data.
While critics will be quick to say that it is my responsibility to show the impact of the error, I view today’s post as part of extended peer review: no author will tell a peer reviewer that it was their job to figure out the impact of using contaminated data. It’s the responsibility of the author to correct contaminated data, not the responsibility of a reviewer, either at the journal stage or in the present “extended” review. I presume that Kaufman will do so, once he has satisfied himself that there is a problem.
In the present case, it may well be that varve compaction – which impacts multiple series – is a more serious problem that a single contaminated series. But one really wonders at the quality of work when such gross errors are made.
Update: 6 pm. The Journal of Paleolimnology article which Mosher located also stated in respect of pollen accumulation:
Despite the possible influence of land use, pollen accumulation appears to document climatic changes of the last millennia nonetheless. PAR reached minimum values during the Little Ice Age from 1500 to 1920 AD, consistent with maximum glacial re-advance at Qipisarqo (Kaplan et al. 2002) and elsewhere in south Greenland (Weidick et al. 2004; Larsen et al. 2011). It is also coeval with high rates of isostatically driven transgression, which caused the inundation of a Norse graveyard at Herjolfsnæs (Mikkelsen et al. 2008). The sharp increase of Salix/ Betula pollen accumulation rate after 1920 AD (Fig. 6) suggests a rapid warming, which reversed the Neoglacial cooling trend similar to other locations in the Arctic (Kaufman et al. 2009).
Nick Stokes has argued in comments below that this is sufficient to qualify the contaminated sediments as a climate proxy. I disagree. The sediments are clearly contaminated by human activity. Can pollen accumulation within contaminated sediments be separated as an indicator? I’ve got a better idea: the Arctic is a big place. Don’t use contaminated sediments.
Postscript: Here is the longer Igaliku pollen accumulation series as plotted from the data at NOAA. Values are low in the mid-Holocene despite other evidence of mid-Holocene warmth. My interpretation of this is that glacier retreat took a long time in this area (think LIFO accounting) and had not retreated sufficiently to permit pollen accumulation until rather late in the Holocene.
Update 4: here is a plot of pollen sum at Unit Lake, Manitoba, one of the data sets published in the Kaufman 2012 JOPL issue.
Update 5: here is a plot of pollen accumulation vs mineral matter accumulation in the same interval for the 7 pollen measurements since 1750. The pollen intervals (1 cm) do not exactly overlap the mineral intervals (0.5 cm) and so weighted averages were taken. There is an obvious relationship between erosion (indicated by mineral matter accumulation) and pollen accumulation. Massa could just as easily “suggested” that erosion was a proxy for temperature.