An ocean-wide study of the rates of removal of 10Be and 231Pa in the Pacific Ocean has identified intensified scavenging of the 10Be and 231Pa in several ocean margin areas, including the Northeastern and Northwestern Pacific, the Bering Sea, the Eastern Equatorial Pacific and the South Pacific Ocean. Scavenging rates of 10Be and 231Pa are clearly correlated to particle flux. Principal component analysis further suggests that scavenging of 10Be and 231Pa may be related to opal productivity in surface waters. A simple box model was constructed to partition the deposition of 230Th, 231Pa and 10Be between open ocean and ocean margin sediments. Model parameters were constrained using measured values of 230Th and 231Pa, which have a common source, and then applied to 10Be. An average Holocene 10Be deposition rate for the entire Pacific Ocean is estimated to be ∼ 1.5 × 106 atoms/cm2 yr-1, with ∼ 70% of the total 10Be supplied to the Pacific being deposited in margin sediments underlying only 10% of the ocean. The short residence times of 10Be in ocean margin regions (from < 100 to ∼ 200 yr) compared to the long 10Be residence time in the central open Pacific Ocean ( ∼ 1000 yr) reflects the intensified scavenging of 10Be in ocean margin waters. The results of this study suggest that the Pacific Ocean acts as a relatively closed basin with respect to the transport and burial of 10Be; therefore, the average 10Be deposition rate in the Pacific Ocean can be used as an estimate of the global average production rate of 10Be in the atmosphere during the Holocene period. © 1992.

BERYLLIUM-10 (half-life 1.5 Myr) is produced by spallation of nitrogen and oxygen atoms by cosmic rays in the upper atmosphere. Its production rate is proportional to the flux of cosmic rays, which is modulated by solar activity and the strength of the Earth's magnetic field1,2. Weakening of the magnetic field allows more cosmic rays to impinge on the Earth's atmosphere, thereby increasing 10Be production. Here we report that the ocean-wide average accumulation rate of 10Be in Pacific sediments, which reflects the global average production rate of 10Be (ref. 3), was at least 25% greater during the height of the most recent ice age (∼ 24,000-16,000 yr ago) than during the Holocene (the past 10,000 yr). The higher production rate of 10Be records the lower intensity of the geomagnetic field during that period and is consistent with the hypothesis developed to explain the younger 14C ages of fossil corals compared with ages obtained by U-Th dating4. These results also point to a more general need to consider variations in production rate in geochronological studies using other cosmogenic nuclides. © 1992 Nature Publishing Group.