Tuesday, April 24, 2012

Northwest Coast Dating Methods

D. C. Drake and Robert J. Naiman.
2007 Reconstruction of Pacific Salmon Abundance from Riparian Tree-Ring Growth. Ecological Applications  17 (5): 1523-1542.
                Salmon were an integral part of society in the past.  Not only were they a good source of calories, but they were also abundant at certain times in the year.  However, they have not always been a dominant food source.  At certain times throughout the history of the Northwest Coast, other marine foods have been eaten more than salmon.  Drake and Naiman have an explanation for this.  Using historical data on salmon abundance, the authors have shown that the tree rings of Northwest Coast sites and the salmon population are strongly correlated.  The obvious reason for this is that changes in the environment affect both trees and salmon.  This is to be expected.  However, the interesting thing about this article is that the two have shown this happens in cycles.  Therefore, it is reasonable to suggest that since the two are strongly correlated in modern periods, they will also be correlated in pre-historical periods.  They suggest that it is possible to estimate the abundance of the salmon population based on the tree rings also used for dendrochronology.  Using this method, the authors showed that it was because of a lack or abundance of salmon that transitions between salmon dependence and independence occurred.

D. W. Clark.
1984 Some Practical Applications of Obsidian Hydration Dating in the Subarctic.  Arctic 37, (2): 91-109.
                Obsidian hydration dating uses the relatively consistent intake of water of obsidian flakes to give an absolute date to a piece of obsidian.  Obsidian hydration dating has been used for several decades in all climates, but is more frequently used in cold climates, especially the Upper Northwest Coast.  The reason it is more useful in cold climates is because temperature has been known to speed up the hydration process by variable amounts.  Still, even the results from cold climates have not been particularly useful.  Because of these failures, many have abandoned the method altogether as useless.  However, in this article, Clark attempts to show that in certain cases obsidian hydration dating is useful.  He gives some suggestions that were not necessarily widely implemented, but were often utilized by the methods where some dates were corroborated by radiocarbon analyses.  Some of these include using a more powerful microscope to examine the water content, keep the flakes in containers with a humidity and temperature consistent with their original location, and taking the average of several pieces sourced to be from the same rock.  Since this article was written, even more powerful methods including new microscopes have been brought in to improve obsidian hydration dating.  I do not know how popular this method is in modern times.

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