Abstract
A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree, located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age (1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density. The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component in this tree may be thermal in origin and was controlled by local thermal condition.
Highlights
A cross section from coast redwood trees (Sequoia sempervirens) in Mountain Home State Forest, California, were dendrochronologically cross-dated (950–1450 years) and detected overall period between 600 and 1700 A.D. [1]
The tree sample was collected in Mountain Home State Forest, California (SE of Fresno), and dated by Rex K
Tree ring density was counted within individual specimens to obtain the tree ring density shown in Figures 2 and 4
Summary
A cross section from coast redwood trees (Sequoia sempervirens) in Mountain Home State Forest, California, were dendrochronologically cross-dated (950–1450 years) and detected overall period between 600 and 1700 A.D. [1]. A cross section from coast redwood trees (Sequoia sempervirens) in Mountain Home State Forest, California, were dendrochronologically cross-dated (950–1450 years) and detected overall period between 600 and 1700 A.D. Tree ring density may detect climatic variations, other factors, like fire frequency can influence tree ring density [2]. Fire paleo-frequency can be detected by variability in formation of pedogenic magnetic particles [3] as well as by variability of paleo-climatic recorders [4]. Sapwood is the physiologically active part of the xylem (wood). This is the tissue through which water with dissolved iron moves from the roots to the shoots. The heartwood is the older, nonliving central wood of a tree that does not conduct water. Once the sapwood becomes hardwood, it is thermally isolated from the out-
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