George posted up the following link as supposedly supporting Lonnie Thompson’s views on Quelccaya:
Early results on Reid Inlet, where Reid Glacier has now backed up out of the ocean, show that the glacier had retreated beyond where it is now more than 10,000 years ago, advanced to the sea by 8,000 years ago, again retreated beyond where it is now about 7,000 years ago, and the ice once again advanced to Reid Inlet beginning about 5,000 years ago.
I’m not sure how the quote supports his position. I haven’t seen any academic publications on the location in question, but collated a little information from abstracts of the authors to conferences over the past few years, showing a curious result.
In 2002, they pointed out that, in the past, the glacier advanced slowly and retreated rapidly:
Past observations of modern tidewater glaciers suggest that these glaciers advance quite slowly (single meters per year) compared to rapid and sometimes catastrophic glacial retreats (tidewater glaciers in Glacier Bay have retreated ~90km in 300 years, or 300 m/yr).
In 2003, they re-affirmed this and, based on radiocarbon dates, reported 4 periods of glacial advance, the most recent being ~1.6 to 1.2 Kyr BP.
Current understanding of the advance and retreat rates of tidewater glaciers suggests that while ice margins can retreat quite rapidly (km/yr), their advance is rather slow (m/yr). Our studies of the glacial history and interglacial climate of Glacier Bay in southeast Alaska indicate that past rates of ice margin advance were highly variable, including periods when ice advanced at rates equivalent to those during a rapid recession. We infer rates of advance during the Holocene from radiocarbon dates of tree stumps that were overridden as ice moved down-fjord. We have sampled over 100 stumps rooted in growth position, and dated their outer rings, which mark the death of the tree, using the AMS technique. In addition, the ages of about 100 logs in glacial deposits of moraines adjacent to the fjords also record approximate ice marginal positions. Our data cover the advance of ice from accumulation areas in the western Fairweather Range and eastern Takhinsha Range into lower Glacier Bay during four apparently distinct periods: ~ 9.5 to 6.0 K radiocarbon years BP, ~ 4.4 to 3.0 Kyr BP, ~2.4 to 2.0 Kyr BP, and ~1.6 to 1.2 Kyr BP.
In 2005, they said that the “most extensive Holocene advance occurred during the Little Ice Age” – a period not mentioned in the 2003 report.
Terminus positions of the tidewater glaciers in Glacier Bay are known reasonably well from radiocarbon dates on stumps rooted in growth position but overridden by advancing ice, and by limited stratigraphic data associated with them. The last glacial maximum (LGM) advance extended well beyond any Holocene position. The post-LGM rise in insolation and greenhouse gases was accompanied by retreat behind the present position prior to 12.5K C14 years BP. An early Holocene advance was initiated prior to 9K C14 years BP, after insolation began falling, and this advance passed the current marginal position by about 8.8-8.4K C14 years BP. The next, more-extensive advance was initiated prior to 5K C14 years BP, at a time when other paleoclimatic data indicate regional cooling and drying, emphasizing the role of summertime temperatures. The most extensive Holocene advance occurred during the Little Ice Age, consistent with the low insolation at that time.
In an abstract for a forthcoming October 2006 conference, from tree ring chronologies, they describe “warming centered on AD 950, and intervals of cooling during the Little Ice Age between the 13th and 19th centuries”.
The millennial to century-scale character of North Pacific climate is clear with cooling in the first millennium, warming centered on AD 950, and intervals of cooling during the Little Ice Age between the 13th and 19th centuries. This ring-width record is one of inferred summer temperature and is consistent with the glacial record from land-terminating glaciers for the region, which is also considered as a proxy of summer temperature.
Aside from the obvious issues, here’s what puzzles me about the sequence: when they reported the original radiocarbon dating of the logs, the most recent reported advance was ~1.6 to 1.2 Kyr BP. I’m not saying that there’s some big gotcha here; I’ve spent about 30 seconds on the topic; but I’m curious as to the non-reporting of any radiocarbon dates associated with the LIA advance.