The NAS panel mentioned the recent 5000-year organics from Quelccaya as being an important potential indicator of 20th century climatic uniqueness. (Lee seems to consider it some kind of smoking gun)
I’ll discuss Thompson’s abysmal publication of the data – in particular, his total lack of any stratigraphic information – in a few days, but first I want to refer to a couple of other articles which also discuss the recover of fossil tree stumps from receding glaciers in a less cavalier way than Thompson.
Wood and Smith 2004 discuss the recovery in 1999 and 2000 of 3000-year old in situ and detrital stumps from stream beds in the valley of the Saskatchewan Glacier, which is the largest outlet glacier of the Columbia Icefield located in northern Banff and southern Jasper National Parks (52o6’30”N;117o15’10”W). This is in the same general area as the Jasper tree rings collected by Luckman and published in Luckman and Wilson 2005 (discussed here here and here previously.) Perhaps one of Schweingruber’s sites comes from this very valley.
Caption Comment: Wood and Smith state that "the glacier flows in a NE direction for ~10 km through a steep-walled valley…Over the last century the Saskatchewan Glacier has experienced significant downwasting and frontal retreat."
Wood and Smith describe the discovery of the stumps, later dated by radiocarbon, as follows:
In late August 1999, a severe rainstorm resulted in stream avulsion along the NE flank of the Saskatchewan Glacier snout (117o8’45”W, 52o9’30”N). When first examined in early September, erosion through a 3- to 5- m sequence of glacial outwash and overlying till had exposed 17 sheared stumps rooted within a well-preserved paleosol (Figure 2). A further 29 recently deposited ice-proximal stimps rooted within a well-preserved paleosol were located 50 to 150 m downstream on the adjacent outwash surface. By September 2000, the meltwater channel had shifter southward and had eroded through 5 m of fluted moraine deposits exposing 2 additional rooted stumps and flushing an additional 40 detrital boles onto the outwash surface.
The stumps were rooted in a deeply weathered pedogenic surface and prior to their exposure were buried by 3-5 m of sediment. …there is an indication that the subfossil samples recovered in 1999 and 2000 were killed between ~2940 and 2760 14C years BP. With one exception, these dates collectively reflect the consequences of a single Neoglacial advance of the Saskatchewan Glacier into an established valley bottom forest.
Here is a picture:
Unfortunately Wood and Smith do not provide a cross-section map of the stratigraphy – something which would be mandatory in any geological presentation. (At least they have a location map and discuss the stratigraphy.) The information is certainly sufficient to deduce that the Neoglacial advance of ~2900-2700 BP overrode the stumps; and that, sediments transported by the glacier sealed the stumps in a 3- to 5-m bed of sediments. It’s my impression that the glacier retreated on at least one subsequent occasion and during that retreat, the forest would have returned upslope – I’m 99% sure that there are medieval trees in this location (since there are upslope trees) , but I would have to confirm this. Granting this assumption for now, such trees would growing in sediments that were above the 3000-year stumps, now sealed in the sediment bed. Think of an archaeolgoical tell in the Middle East with destroyed cities in strata on top of each other, older the deeper.
It’s my understanding that the LIA glacial advance in the Canadian Rockies was the largest since the last Ice Age (ending in the 19th and even early 20th centuries.) Presumably this advance may have bulldozed some of the overlying sediments further downslope, rendering it possible for the 3000-year old stumps to be exposed by stream erosion in the 20th century, as has happened.
If trees have grown upslope at any point during the past 3000 years, the discovery of rooted stumps in 1999-2000 does not imply anything about the uniqueness of the present glacier retreat. One needs much more information before any such conclusions can be considered: one needs information about the stratigraphy of the organics and an inventory of all other organics together with their stratigraphy. You also see why one wants to have a careful exposition of the discovery of Quelccaya organics, rather than Lonnie Thompson’s typical pamphleteering account, which unfortunately was accepted by PNAS as a scientific report.
Wood, C., Smith, D. 2004. Dendroglaciological evidence for a Neoglacial advance of the Saskatchewan Glacier, Banff National Park, Canadian Rocky Mountains. Tree-Ring Research 60(1):59-65. url
Thompson, 2006, PNAS.