A 200 KYR RECORD OF COSMOGENIC RADIONUCLIDE PRODUCTION-RATE AND GEOMAGNETIC-FIELD INTENSITY FROM BE-10 IN GLOBALLY STACKED DEEP-SEA SEDIMENTS

The reconstruction of geomagnetic field intensity variations during th e last 200 kyr from paleomagnetic data is at present the subject of nu merous studies and major debate. There is currently no generally accep ted record. Here we present a global stacked record of (Th-230(ex)-nor malized) Be-10 deposition in marine sediments representing relative va riations in Be-10 production rate which are translated into field inte nsity variations, The record shows major periods during which the fiel d intensity was between 10% and 40% of the present day value; namely 3 0-42, 60-75, 85-110 and 180-192 kyr B.P. Our results are compared to i ndependently derived paleomagnetic studies and Th/U calibrations of C- 14 dates on corals. During most of the observed period the geomagnetic field intensity was weaker than today, resulting in an overall 30% re duced value for the last 200 kyr.