Continuous inclination record of the geomagnetic field from a Brazilian stalagmite

It is known that South America contributes with less than ~3% of the global database and some of these data (obtained decades ago) do not obey minimum quality criteria, such as standard deviations and age controls. In this sense, continuous full-vector records (direction and intensity) provide important high-resolution data on the spatial and temporal behavior of Earth's magnetic field of utmost importance to describe the evolution of major field features, such as the South Atlantic Magnetic Anomaly (SAMA). Here, we present results of magnetic inclination determined from a stalagmite collected in Pau d'Alho cave located at 14.8° S, 56.4° W (Mato Grosso, Brazil), where no previous geomagnetic record was available. The sample is a 23-cm-long stalagmite which grew continuously during most of the last 1400 years. The chronology based on high-quality U-Th dating ranges from 500 AD to 1900 AD and reveals a nearly constant growth rate of ~150 μm/yr. Remanence measurements of the stalagmite were performed continuously using a SQUID magnetometer with a spatial resolution of 0.5 cm. Magnetic values for each measured point were deconvolved using the singular value decomposition (SVD) method. Hysteresis and low-temperature magnetization analyses indicate a very homogeneous magnetic mineralogy with the presence of tiny concentrations of pure magnetite in the SD-PSD state. After stepwise alternating field demagnetization, inclination data show maximum angular deviation (MAD) for most samples below 5° (with anomalous MAD of up to 15° for the 1660 AD to 1690 AD period). In general, our magnetic inclination data are consistent with those predicted by geomagnetic field models, and will provide a firm observational anchor for future modeling efforts. In this way, continuous magnetic measurements on speleothems can provide important, high-quality information about the short term behavior of the geomagnetic field.