IMPLICATIONS OF DIPOLE-MOMENT SECULAR VARIATION FROM 50,000-10,000 YEARS FOR THE RADIOCARBON RECORD

Sparse paleointensity data from 10-50 ka suggest that the average dipole moment (DM) was 50-75% of the average of 8.67 x 10(22) A m2 for the past 5 Ma, and 8.75 x 10(22) for the past 12 ka. A linear ramp function, increasing the DM from 4 to 8.75 X 10(22) A M2 between 50-10 ka BP, generates a total C-14 inventory of 126 dpm/cm(e)2, agreeing very well with an inventory assay of 128 dpm/cm(e)2, which includes C-14 in sediments. With the Lingenfelter and Ramaty (1970) production function and a model DC gain of about 100, this DM function would give a DELTAC-15 of 500 parts per thousand at 20 ka BP, consistent with the Barbados coral record, and also gives a good match to the Holocene record. A Laschamp geomagnetic event at about 45 ka BP, with a DM of 25% of its average value and lasting 5 ka, would only increase the present inventory by 0.3-1.2 dpm/cm(e)2, and would probably have only a small effect on DELTA C-14 at 20 ka BP, but could produce a short-lived C-14 spike of over 500 parts per thousand.