This post is going to be a bit more interesting than my last one, where I was getting some preliminary information out of the way. The post here draws heavily on Mauri Timonen’s 2009 PPT, which explains how their 7500-year long chronology is obtained. I’m also going to get to some results which will intrigue many readers.
In small lakes in Finnish Lapland, there are hundreds of submerged Scots pine logs that can be thousands of years old. (BTW the countryside and topography of these photographs looks very familiar to a Canadian). On the left below is a picture of an underwater logs (later determined to be from about 2000 BC); on the right is a montage of pictures showing the recovery of the logs and the taking of sample disks: these obviously give better data than pencil thin drill holes where perpendicularity is hard to maintain and where the pith is not known for certain.
Fnland has been surprisingly successful in high-tech for a small country. Here is an example of high-tech 🙂 methods being applied to the recovery of ancient logs. What I actually want readers to notice is that the trees are all scrub birch trees; there isn’t a pine tree in sight. The pine treeline is some tens of km to the south.
Figure 2. Lohikoste, Utsjoki (compare to Eronen et al 2002 Figure 1).
Timonen shows pictures of present-day alpine meadows and invites his audience to imagine a Holocene pine forest. For example, here is a picture from Enontekio, where the legend explains that there are submerged logs about 1 m below the surface of the small lake, with the stumps still in situ.
The tree zones are nicely shown in the map below (from Rudner and Seppala), which distinguishes between alpine heath (white), scruffy birch (yellow), with a mixed pine/birch zone shown in orange. The various sites shown in the Metla pictures (Lohikoste, Vallijarvi) are to the north of the pine treeline, well into the yellow zone.
Kultti et al (Holocene 2006) (picture below is from Kultii et al 2003 poster) shows their estimates of past treeline locations from these extensive surveys. The treeline denominated +0.57 deg C corresponds to the MWP, while the treeline denominated +2.4 deg C corresponds to the Holocene Optimum.
Here is the corresponding figure (Figure 5) from Kultti et al 2006, discussed briefly at CA in 2006 here, clearly showing their estimates of MWP temperature (+0.55 deg C), 3000 BP (+0.96 deg C) and 6000 BP (2.55 deg C.) They reported:
Between c. 8000 and 4000 cal. yr BP pines were growing at 350/400 m higher altitudes than at present and the shift in mean July temperatures compared with 1961/1990 climate normals was ~2.5/2.6 deg C. … During the ‘Mediaeval Warm Period’ the distribution area of pine was 7200 km2 more extensive than at present, and pines were growing at 40/80 m higher altitudes. For this period, the mean July temperature reconstruction
shows ~0.55 deg C shift compared with the present.
These estimates are based on treelines – a method that I find intuitively appealing. I’ll discuss temperature estimates based on ring-width chronologies in another post. In an email to me, Timonen clearly distinguished between using ring width chronologies to establish dates (their original purpose) and using ring width chronologies for temperature reconstructions (which he regards as considerably more speculative).
I’ll also discuss IPCC AR4 handling of treeline issues; while the issue is not discussed in AR4 itself (nor are the Finnish studies), this point was raised by one reviewer and IPCC reasoning for excluding such results will interest some readers.
Timonen, M. 2009-Jan-05. An updated version of “Studies on past and present climate change in Finnish Lapland, based on the 7642-yr supra-long pine chronology for Finnish Lapland;
Pdf (14 MB). This presentation was originally held 23-Oct-2007 in the “Forest Science Day” seminar.http://lustiag.pp.fi/MTP_231007.pdf
Timonen, M. 2007. Past, Present and Future Climate from Tree-Rings. Studies on past and present climate change in Finnish Lapland, based on the 7641-yr supra-long pine chronology for Finnish Lapland. Pdf (13 MB). Forest Science Day 23-Oct-2007, arranged by The Finnish Society of Forest Science and Taksaattoriklubi, themed as “Adaptation to climate change and Finnish Forests”. The House of Sciences (Tieteiden talo), Kirkkokatu 6, Helsinki, Finland.
Kultti, S., Mikkola, K., Virtanen, T., Timonen, M. & Eronen, M. 2006. Past changes in the Scots pine forest line and climate in Finnish Lapland: a study based on megafossils, lake sediments, and GIS-based vegetation and climate data. The Holocene 16(3): 381-391. Pdf
Kultti, S., Mikkola, K., Virtanen, T., Timonen, M. & Eronen, M. 2003. Past changes in the Scots pine treeline and climate in Finnish Lapland – evidence from pine megafossils and lake sediments. Pdf. Eurodendro 2003 10-14 September 2003. University of Innsbruck, Institute of High Mountain Research, Innsbruck, Austria.
Rudner, Seppala http://www.helsinki.fi/geography/research/RZEposterKilpisj.pdf