Abstract
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 × 10 6 atoms/cm 2 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.
Highlights
In order to evaluate the source of l°Be, and to understand its transport within the oceans, we need to conduct an ocean-wide study: (1) to estimate the extent to which l°Be deposition is enhanced in different ocean margin regions; and (2) to examine what factors influence the scavenging of l°Be from seawater to sediments
Boundary scavenging exerts some influence on 23°Th [24], so that the actual enhancement of the deposition of 231pa and 1°Be in ocean margin sediments should be obtained by multiplying the Pa/Th and Be/Th ratios by the extent to which 23°Th deposition is enhanced at margins. Despite these conditions, which lead to minimum estimates of enhanced scavenging at margins, the depth normalized Be/Th ratios ([Be/Th] N) still span a full order of magnitude (Fig. 4b), providing unequivocal evidence for greatly enhanced scavenging of 1°Be in ocean margin areas
One of our goals is to evaluate an ocean-wide l°Be deposition rate which, in turn, provides an estimate of global average production rate of 1°Be in the atmosphere
Summary
TRANSPORT AND BURIAL RATES OF l°Be AND 231pa IN THE PACIFIC margin regions where fluxes of ~°Be collected by sediment traps indicate that scavenging takes place throughout the water column [24], in which case the depth normalization will underestimate the actual enhancement of ~°Be deposition. Another factor which causes estimates of the extent of boundary scavenging of 23~pa and 1°Be, based on Pa/Th and Be/Th ratios, to be minimum values is the assumption that the deposition rate of 23°Th is everywhere equal to its production rate in the overlying water column. Despite these conditions, which lead to minimum estimates of enhanced scavenging at margins, the depth normalized Be/Th ratios ([Be/Th] N) still span a full order of magnitude (Fig. 4b), providing unequivocal evidence for greatly enhanced scavenging of 1°Be in ocean margin areas
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