标题： 海洋生态系统中$^{236}$U 和$^{237}$Np 的存在：北本格拉上升流系统案例研究 显示英文标题

标题： Presence of $^{236}$U and $^{237}$Np in a marine ecosystem: the northern Benguela Upwelling System, a case study

摘要： 本格拉上升流系统（BUS），位于非洲西南海岸，是海洋中的四大主要东边界上升流生态系统之一。 然而，尽管具有非常有趣的特性，该地区在环境放射性领域几乎被忽视。 在这项工作中，首次在北部 BUS 的纳米比亚沿岸进行了$^{236}$U 和$^{237}$Np 的综合研究。 表层海水中的$^{236}$U 和$^{237}$Np 浓度相似，分别在$3.9\times10^6$到$5.6\times10^6$个/千克和$4.6\times10^6$到$8.5\times10^6$个/千克之间。 从大陆边缘水柱中观察到的库存，对于 $(2.10 \pm 0.11)\times10^12$ 原子/米$^{-2}$ 的 $^{236}$U 和 $(3.48 \pm 0.13)\times10^{12}$ 原子/米$^{-2}$ 的 $^{237}$Np，与南半球的全球沉降（GF）源项一致，该源项被认为是该地区锕系元素的主要来源。 在表层样品中观察到一种模式，$^{237}$Np浓度从近岸站向远岸站移动时减少了25-30%，但在$^{236}$U的情况下，由于数据不确定性，这种影响无法清晰辨识。 提出了一个解释，即GF$^{237}$Np比GF$^{236}$U具有更大的颗粒反应性。 由于上升流现象导致大陆架区域颗粒物的增加，这种效应在研究地点非常重要。 在海洋环境中，GF源项的$^{237}$Np/$^{236}$U原子比值获得了一个值为$1.77 \pm 0.20$。 显示英文摘要

摘要： The Benguela Upwelling System (BUS), off the south-western African coast, is one of the four major eastern boundary upwelling ecosystems in the oceans. However, despite its very interesting characteristics, this area has been almost overlooked in the field of environmental radioactivity. In this work, it has been carried out for the first time the combined study of $^{236}$U and $^{237}$Np in the coast of Namibia within the northern BUS. Surface seawater exhibited similar $^{236}$U and $^{237}$Np concentrations, ranging from $3.9\times10^6$ to $5.6\times10^6$ atoms/kg and from $4.6\times10^6$ to $8.5\times10^6$ atoms/kg, respectively. The observed inventories in a water column from the continental margin, of $(2.10 \pm 0.11)\times10^12$ atoms m$^{-2}$ for $^{236}$U and $(3.48 \pm 0.13)\times10^{12}$ atoms/m$^{-2}$ for $^{237}$Np, were in agreement with the global fallout (GF) source term in the Southern Hemisphere, which was recognized as the main source of actinides to the region. A pattern was observed in the surface samples, with $^{237}$Np concentrations that decreased by 25-30% when moving from inshore to offshore stations, but such an effect could not be clearly discerned in the case of $^{236}$U within the data uncertainties. An explanation based on the larger particle reactivity of GF $^{237}$Np compared to GF $^{236}$U was proposed. Such an effect would have been important at the studied site due to the enhance presence of particles in the continental shelf triggered by the upwelling phenomenon. A value of $1.77 \pm 0.20$ was obtained for the $^{237}$Np/$^{236}$U atom ratio for the GF source term in the marine environment.