Testing for Links Between Geomagnetic Field Variability and Climate Change
Laura Wetter, Gary Acton, and Tessa Hill
Department of Geology, University of California, Davis, One Shields Avenue, Davis, CA 95616
Although orbital forcing controls much of long-term climate change and increases in greenhouse gases are thought to be driving recent global warming, other factors may also play a significant role. Recent studies have hypothesized various forms of links between climate change and solar irradiance, solar activity, and cosmic ray flux. Because changes in geomagnetic field strength affect the cosmic ray flux, it is possible that changes in the geomagnetic field contribute to long- and short-term climate change. Alternatively, it has been hypothesized that geomagnetic field variability is influenced by climate change or solar activity. We test such claims through a paleomagnetic and stable isotope study of Ocean Drilling Program (ODP) sediment cores from the Blake Outer Ridge (BOR), western North Atlantic Ocean. The goal of the study is to create a continuous, high-resolution record of geomagnetic field variability with an accurate, astronomically tuned chronology.
Sediment cored on the BOR in four holes at Site 1061 during ODP Leg 172 is being used for this investigation. The high sedimentation rate, averaging 22 cm/k.y. over the Brunhes, and the exceptional paleomagnetic properties of the area make Site 1061 an excellent candidate to test for links between short- term geomagnetic events and climate. The paleomagnetic record, originally constructed mainly from continuous split-core measurements, is being refined and rock magnetic analyses are being conducted on U- channel samples that span the Brunhes. We have also refined the between-hole correlation and constructed a more detailed composite stratigraphic section for Site 1061 in order to improve the continuity and relative chronology of the record and to confirm the existence of distinct geomagnetic excursions and other short-term events in multiple drill holes. Additionally, planktonic forams are being measured for δ18 O variations across, and extending to one meter beyond each observed excursion, allowing for direct tie-points between the geomagnetic and the marine oxygen isotopic record. Using these data, the timing of climatic events such as glaciations, stadials and interstadials will be compared with large scale variations in geomagnetic field strength or direction in hopes of finding conclusive results that will either confirm or refute the possible link between the two records.
