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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.


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Thermal demagnetization of Saturation Isothermal Remanent Magnetization of selected samples, indicated by age, normalized by the magnetic remanence at room temperature (Mt, s/Ms). Derivative is based on the smoothed trend of thermal demagnetization. Magnetic susceptibility after each heating step is shown below remanence plots sharing the temperature axis. The remanence data are approximated with Stineman function. The output of this function then has a geometric weight applied to the current point and ± 10% of the data range, to arrive at the smoothed curve. Data are taken at Pruhonice Paleomagnetic Laboratory (noise limit on JR-5A spinner is 0.0024 mA/m).
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Figure 5: Thermal demagnetization of Saturation Isothermal Remanent Magnetization of selected samples, indicated by age, normalized by the magnetic remanence at room temperature (Mt, s/Ms). Derivative is based on the smoothed trend of thermal demagnetization. Magnetic susceptibility after each heating step is shown below remanence plots sharing the temperature axis. The remanence data are approximated with Stineman function. The output of this function then has a geometric weight applied to the current point and ± 10% of the data range, to arrive at the smoothed curve. Data are taken at Pruhonice Paleomagnetic Laboratory (noise limit on JR-5A spinner is 0.0024 mA/m).

Mentions: The PPL obtained NRM and SIRM from sister samples (Figure 4) using JR-5A Spinner Magnetometer (measuring range from 2.4 e-3 to 1.6 e+3 mA/m). SIRM was acquired in an electromagnet (Polytechnik, Germany) using a direct magnetic field to the state of saturation at the maximum field intensity of 1 T. SIRM of 12 selected samples were partially thermally demagnetized (Figure 5) with MAVACS (Magnetic Vacuum Control System). This instrument creates a magnetic vacuum less than 1 nT [10]. Each demagnetization step was followed by measurement of magnetic susceptibility (frequency 875 Hz, field intensity 300 A/m) with KLY-2 Kappabridge [9]. Changes in magnetic susceptibility indicate chemical changes within the sample during the heating (see Figure 5). Five samples with SIRM from the older section of the tree (600–1000 years A.D.) were demagnetized by alternating field up to 0.1 T with instrument Schonstedt GSD-1 demagnetizer and subsequently stepwise magnetized by field up to 0.5 T. All magnetic remanence measurements were done such that samples were kept oriented in respect to each other. NRM magnetizations from all samples stayed within +/- 30 degrees (see PPL data set, Figure 6).


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

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

Thermal demagnetization of Saturation Isothermal Remanent Magnetization of selected samples, indicated by age, normalized by the magnetic remanence at room temperature (Mt, s/Ms). Derivative is based on the smoothed trend of thermal demagnetization. Magnetic susceptibility after each heating step is shown below remanence plots sharing the temperature axis. The remanence data are approximated with Stineman function. The output of this function then has a geometric weight applied to the current point and ± 10% of the data range, to arrive at the smoothed curve. Data are taken at Pruhonice Paleomagnetic Laboratory (noise limit on JR-5A spinner is 0.0024 mA/m).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Thermal demagnetization of Saturation Isothermal Remanent Magnetization of selected samples, indicated by age, normalized by the magnetic remanence at room temperature (Mt, s/Ms). Derivative is based on the smoothed trend of thermal demagnetization. Magnetic susceptibility after each heating step is shown below remanence plots sharing the temperature axis. The remanence data are approximated with Stineman function. The output of this function then has a geometric weight applied to the current point and ± 10% of the data range, to arrive at the smoothed curve. Data are taken at Pruhonice Paleomagnetic Laboratory (noise limit on JR-5A spinner is 0.0024 mA/m).
Mentions: The PPL obtained NRM and SIRM from sister samples (Figure 4) using JR-5A Spinner Magnetometer (measuring range from 2.4 e-3 to 1.6 e+3 mA/m). SIRM was acquired in an electromagnet (Polytechnik, Germany) using a direct magnetic field to the state of saturation at the maximum field intensity of 1 T. SIRM of 12 selected samples were partially thermally demagnetized (Figure 5) with MAVACS (Magnetic Vacuum Control System). This instrument creates a magnetic vacuum less than 1 nT [10]. Each demagnetization step was followed by measurement of magnetic susceptibility (frequency 875 Hz, field intensity 300 A/m) with KLY-2 Kappabridge [9]. Changes in magnetic susceptibility indicate chemical changes within the sample during the heating (see Figure 5). Five samples with SIRM from the older section of the tree (600–1000 years A.D.) were demagnetized by alternating field up to 0.1 T with instrument Schonstedt GSD-1 demagnetizer and subsequently stepwise magnetized by field up to 0.5 T. All magnetic remanence measurements were done such that samples were kept oriented in respect to each other. NRM magnetizations from all samples stayed within +/- 30 degrees (see PPL data set, Figure 6).

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