Particulate fluxes of [sup 230]Th, [sup 231]Pa, and [sup 10]Be in the northeastern Pacific Ocean

Measurements of [sup 230]Th, [sup 231]Pa, and [sup 10]Be in sediment trap samples and Holocene sediments collected along a transect in the northeastern Pacific indicate that the removal of these nuclides from the ocean is greatly influenced by boundary scavenging. More than 35% of the [sup 230]Th, at least 70% of the [sup 231]Pa, and as much as 85% of the [sup 10]Be fluxes collected by sediment traps at a nearshore site (located [approximately] 120 km off shore) are supplied by lateral transport of the dissolved nuclides from the open ocean. These findings are consistent with the hypothesis that boundary scavenging is proportional to the oceanic residence times of the nuclides (10-40 y for [sup 230]Th, [approximately] 100 y for [sup 231]Pa, and [approximately] 1,000 y for [sup 10]Be). Results of this study indicate that particle flux is a principal factor influencing scavenging of [sup 230]Th, [sup 231]Pa, and [sup 10]Be from the water column. The marine geochemistry of [sup 10]Be in ocean-margins is fundamentally different from that in the open ocean. Scavenging of [sup 10]Be occurs throughout the water column at the margin area in this study, in contrast to the pattern of [sup 10]Be being removed only in the surface waters and then remineralized at depth in the open ocean. Aluminosilicate may be a major phase removing [sup 10]Be from the water column in the open ocean but not at ocean-margins. Nuclide accumulation rates in the underlying Holocene sediments are all higher than the corresponding fluxes collected by sediment traps. Several possibilities that could account for this observation include: downslope sediment transport; deployment of the traps during a period when the particle flux was not representative of long-term average conditions; and scavenging of the nuclides from near bottom waters. 42 refs., 10 figs., 7 tabs.