Limits...
Magnetic record associated with tree ring density: possible climate proxy.

Kletetschka G, Pruner P, Venhodova D, Kadlec J - Geochem. Trans. (2007)

Bottom Line: A magnetic signature of tree rings was tested as a potential paleo-climatic indicator.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Geology, AS CR, Prague, 16502, Czech Republic. kletetschka@nasa.gov

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.

No MeSH data available.


Related in: MedlinePlus

Efficiency of magnetization that approximate "heat index" is plotted as a function of age for samples of Sequoia sempervirens. Top of the diagram shows intervals for the Medieval Warm Epoch period [11] and for Little Ice Age [12].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC1851700&req=5

Figure 7: Efficiency of magnetization that approximate "heat index" is plotted as a function of age for samples of Sequoia sempervirens. Top of the diagram shows intervals for the Medieval Warm Epoch period [11] and for Little Ice Age [12].

Mentions: It is conceivable that magnetic grains warm above their blocking temperatures during heat anomaly events (fire/drought) and cool down to block the thermal remanent component. The relative magnetic signature fluctuation is noisier for NRM data set than SIRM (Figure 4) and this possibly relates to a demagnetization event that may have influenced the original remanence after it was acquired in nature. We infer several NRM components. The first component is chemical remanence (CRM) because we assume that the magnetic minerals had to be formed from within the tree tissue below the blocking temperatures of the remanence carriers. Under ambient temperature a significant fraction of the grains is likely to be in the superparamagnetic (SP) domain state with grain size <30 nm. Therefore, the second NRM component can be partial thermoremanent magnetization with blocking temperatures that span across the ambient temperatures. Some evidence supporting this claim is in Figure 5, where the SIRM is rapidly declining during the partial thermal demagnetization in ambient air. The rapid decay is due to thermal unblocking of the remanence. Because of the steepness of the slope, it may be conceivable that daily heating due to weather may continuously block and unblock parts of the remanence. When anomalous heating has been recorded it is sealed from the future thermal fluctuations by additional wood growth. We must say, however, that prolonged storage of these samples containing SP grains could also generate a third component of viscous remanent magnetization (VRM) adding to the overall value of NRM. For example assuming that the subset of these samples had large amount of SP grains, they would be prone to viscous re-magnetization, most likely randomizing the original signature. If this would be the case we would observe significant directional deviation of NRM within the sample set. In Figure 6, we plot directions of the PPL data set and show that only few samples (6 out of 27) may have considerable directional change, and indeed, the angular deviation of the largest outliers is associated with the low sample efficiencies in Figure 7.


Magnetic record associated with tree ring density: possible climate proxy.

Kletetschka G, Pruner P, Venhodova D, Kadlec J - Geochem. Trans. (2007)

Efficiency of magnetization that approximate "heat index" is plotted as a function of age for samples of Sequoia sempervirens. Top of the diagram shows intervals for the Medieval Warm Epoch period [11] and for Little Ice Age [12].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1851700&req=5

Figure 7: Efficiency of magnetization that approximate "heat index" is plotted as a function of age for samples of Sequoia sempervirens. Top of the diagram shows intervals for the Medieval Warm Epoch period [11] and for Little Ice Age [12].
Mentions: It is conceivable that magnetic grains warm above their blocking temperatures during heat anomaly events (fire/drought) and cool down to block the thermal remanent component. The relative magnetic signature fluctuation is noisier for NRM data set than SIRM (Figure 4) and this possibly relates to a demagnetization event that may have influenced the original remanence after it was acquired in nature. We infer several NRM components. The first component is chemical remanence (CRM) because we assume that the magnetic minerals had to be formed from within the tree tissue below the blocking temperatures of the remanence carriers. Under ambient temperature a significant fraction of the grains is likely to be in the superparamagnetic (SP) domain state with grain size <30 nm. Therefore, the second NRM component can be partial thermoremanent magnetization with blocking temperatures that span across the ambient temperatures. Some evidence supporting this claim is in Figure 5, where the SIRM is rapidly declining during the partial thermal demagnetization in ambient air. The rapid decay is due to thermal unblocking of the remanence. Because of the steepness of the slope, it may be conceivable that daily heating due to weather may continuously block and unblock parts of the remanence. When anomalous heating has been recorded it is sealed from the future thermal fluctuations by additional wood growth. We must say, however, that prolonged storage of these samples containing SP grains could also generate a third component of viscous remanent magnetization (VRM) adding to the overall value of NRM. For example assuming that the subset of these samples had large amount of SP grains, they would be prone to viscous re-magnetization, most likely randomizing the original signature. If this would be the case we would observe significant directional deviation of NRM within the sample set. In Figure 6, we plot directions of the PPL data set and show that only few samples (6 out of 27) may have considerable directional change, and indeed, the angular deviation of the largest outliers is associated with the low sample efficiencies in Figure 7.

Bottom Line: A magnetic signature of tree rings was tested as a potential paleo-climatic indicator.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Geology, AS CR, Prague, 16502, Czech Republic. kletetschka@nasa.gov

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.

No MeSH data available.


Related in: MedlinePlus