| 英文摘要: | Geomagnetic field excursions (e.g., Laschamp Excursion, Blake Event) are intervals of very anomalous magnetic field variability located within one region of the Earth's surface that last for less than a few thousand years. There have been, perhaps, 15 excursions since the last global magnetic field reversal ~780,000 years ago. Excursions must be due to some intermittent and anomalous behavior in the magnetic dynamo situated deep in the Earth's outer core, which generates the Earth's magnetic field. However, we have very little evidence of the pattern of individual excursions in several global regions far apart from one another that would test ideas of dynamo source(s) for excursions. We have no evidence for the relationship of excursions to surrounding normal magnetic field secular variation beyond individual records at isolated localities. Scientists still wonder whether excursions might be aborted global magnetic field reversals - or not. This grant would add significantly to our understanding of what individual excursions really look like around the world and how they relate to normal secular variation. Both of these are key concepts in building more realistic models of dynamo causes of excursions. The regional environmental magnetic correlations and paleomagnetic chronostratigraphic framework that the PI team will develop within the Equatorial Atlantic study region, will also provide significant insight into the space/time pattern of equatorial paleoclimate variability, of keen interest to global climate change policy.
This grant will carry out a paleomagnetic study of excursions and surrounding normal secular variation recorded in deep-sea sediments of the Equatorial West Atlantic Ocean over the last glacial cycle (0-71 ka, MIS 1-4). This time interval contains the Mono Lake Excursion (~34 ka, Ex. 3a), the Laschamp Excursion (~41 ka, Ex. 3b) and the Greenland/Norwegian Sea Excursion (~61 ka, Ex. 4a). There are almost no published records of excursions at equatorial latitudes or of excursion records with reproducible secular variation surrounding them. This study also will develop, for the first time, a transect of excursion records and surrounding normal secular variation that extends from ~40°S to ~40°N along a single longitude swath (290°±20°). This transect will provide the first evidence of the detailed space/time pattern of excursions and their relationship to surrounding normal secular variation ever developed over a large, almost hemispheric, region of the Earth. |