A Test of Paleomagnetic Field Variability at Equatorial Latitudes

University Of Southern California, Los Angeles CA

Investigators

Abstract

Lund 0106685 Paleomagnetic studies of the Earth' magnetic field secular variation (PSV, both directions and paleointensity) require knowledge of its spatial and temporal pattern of variability. At present, we have no detailed PSV records in Equatorial regions prior to the last 3000 years. Yet, several recent models of field variability require an understanding of Equatorial PSV in order to properly interpret PSV records at other latitudes and make predictions about possible dynamo sources in the Earth's deep interior. This proposal has five scientific goals. (1) recover two replicate deep-sea sediment PSV records (both directions and paleointensity) spanning the last 130,000 years from Equatorial latitudes in Indonesia/Philippines, (2) carry out a careful rock magnetic study of all sediments (magnetic mineralogy, ARM, IRM, CHI, plus selected AMS and hysteresis measurements) to assess where environmental effects might be biasing the directional or paleointensity data, (3) carry out a detailed statistical study of the final PSV records focussing on the temporal variability of vector and VGP angular dispersion associated (almost entirely) with quadrapole-family dynamo sources, (4) carry out a comparison of all Holocene PSV records extending from Lake Baikal (Russia) to Lake Pounui (New Zealand) including the new records from this study, (5) compare the PSV records of the Laschamp and Blake excursion time intervals in these cores with similar PSV records from the North Atlantic Ocean. Final paleomagnetic datasets will be available on the PI's website (http://earth.usc.edu/~slund). The investigators' previous work indicates that they can recover high-resolution PSV records (both directions and paleointensity) for the last 130,000 years from several deep-sea cores in the Equatorial Indonesia/Philippines region. Their preliminary PSV data suggest that times of low paleointensity have higher PSV angular dispersion in both Equatorial and higher-latitude bands, but the relative increase in dispersion at Equatorial latitudes appears to be significantly greater. Assuming that the quadrapole-family dispersion level is constant as a function of latitude, it could be that the quadrapole family of dynamo sources is the sole cause of PSV dispersion at mid latitudes during the Laschamp excursion! They have also recovered an excursion record equivalent in time to the Laschamp Excursion. Comparison of this record with detailed Laschamp Excursion records from the mid-latitude North Atlantic Ocean suggests that the excursions on opposite sides of the Earth are virtually identical in age. Both regions have waveform characteristics of Class I excursions, but the Laschamp excursion in the North Atlantic Ocean has two cycles of clockwise-looping excursional VGPs while the Equatorial excursion has two cycles of counterclockwise-looping excursional VGPs. Careful comparisons of the proposed Equatorial PSV records with data from other latitude bands should provide significant new insight into magnetic field variability and dynamo processes that cause it.