PB-210-RA-226 AND PO-210-PB-210 DISEQUILIBRIA IN SEAWATER AND SUSPENDED PARTICULATE MATTER
PB-210-RA-226 AND PO-210-PB-210 DISEQUILIBRIA IN SEAWATER AND SUSPENDED PARTICULATE MATTER
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DOI：
10.1016/0012-821x(76)90068-6
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发表时间：
1976-01-01
影响因子：
5.3
通讯作者：
BREWER, PG
中科院分区：
文献类型：
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作者：
BACON, MP;SPENCER, DW;BREWER, PG
在热带和北大西洋东部的10个站和太平洋的两个站测量了溶解相（<0.4 μm）和颗粒相（>0.4 μm）的~（210）Po和~（210）Po的分布。这两种放射性核素主要存在于溶解相中。来自大气的通量维持着未被污染的210 Pb活动，存在于表面混合层中，并渗透到温跃层中约500 m的深度。溶解的210 Po通常存在于混合层中，低于平衡浓度，这表明快速生物去除这种核素。颗粒物富集210 Po，210 Po/210 Pb活度比值大于1.0，与浮游植物相似。箱形模型计算得到210 Pb在混合层中的停留时间为2.5年，210 Po在混合层中的停留时间为0.6年。这些停留时间明显长于混合层中颗粒周转的计算时间（约0.1年）。在100-300 m深度，210 Po极大值出现，未被捕获的210 Po经常出现。计算表明，至少有50%的210 Po从混合层中被回收的温跃层内。对210 Pb的类似计算表明再循环效率要低得多。将210 Pb分布与附近GEOSECS站报告的226 Ra分布进行比较，证实了深海中普遍存在210 Pb/226 Ra不平衡。利用210 Pb颗粒的垂直剖面资料，验证了210 Pb通过原位清除作用从深水中去除的假设。除了在大西洋中脊附近的一个剖面外，没有观察到颗粒210 Pb浓度的显著垂直梯度，因此有必要调用异常高的颗粒沉降速度来解释推断的210 Pb通量。相反，有人建议，必须在深海中寻找210 Pb的另一个汇。在深度大于1000米的dissolved 210 Pb/226 Ra的活动比的估计范围从0.2到0.8，并揭示了一个系统的增加，在垂直和水平方向上，随着距离海底的增加。这一观察结果意味着沉积物-水界面处210 Pb的快速清除，并且与3 - 6 × 107 cm 2/秒的水平涡流扩散率一致。另一方面，更具反应性的元素Po显示出快速原位清除的证据。在过滤后的海水中，210 Po平均不足约1000克。10%相对于210铅;相应的富集被发现在颗粒相。然而，整个水体中210 Pb和210 Po的总储量与长期平衡没有明显的偏离。
The distribution of210Po and210Po in dissolved (<0.4 μm) and particulate (>0.4 μm) phases has been measured at ten stations in the tropical and eastern North Atlantic and at two stations in the Pacific. Both radionuclides occur principally in the dissolved phase. Unsupported210Pb activities, maintained by flux from the atmosphere, are present in the surface mixed layer and penetrate into the thermocline to depths of about 500 m. Dissolved210Po is ordinarily present in the mixed layer at less than equilibrium concentrations, suggesting rapid biological removal of this nuclide. Particulate matter is enriched in210Po, with210Po/210Pb activity ratios greater than 1.0, similar to those reported for phytoplankton. Box-model calculations yield a 2.5-year residence time for210Pb and a 0.6-year residence time for210Po in the mixed layer. These residence times are considerably longer than the time calculated for turnover of particles in the mixed layer (about 0.1 year). At depths of 100–300 m,210Po maxima occur and unsupported210Po is frequently present. Calculations indicate that at least 50% of the210Po removed from the mixed layer is recycled within the thermocline. Similar calculations for210Pb suggest much lower recycling efficiencies.Comparison of the210Pb distribution with the reported distribution of226Ra at nearby GEOSECS stations has confirmed the widespread existence of a210Pb/226Ra disequilibrium in the deep sea. Vertical profiles of particulate210Pb were used to test the hypothesis that210Pb is removed from deep water by in-situ scavenging. With the exception of one profile taken near the Mid-Atlantic Ridge, significant vertical gradients in particulate210Pb concentration were not observed, and it is necessary to invoke exceptionally high particle sinking velocities to account for the inferred210Pb flux. It is proposed instead that an additional sink for210Pb in the deep sea must be sought. Estimates of the dissolved210Pb/226Ra activity ratio at depths greater than 1000 m range from 0.2 to 0.8 and reveal a systematic increase, in both vertical and horizontal directions, with increasing distance from the sea floor. This observation implies rapid scavenging of210Pb at the sediment-water interface and is consistent with a horizontal eddy diffusivity of 3−6 × 107cm2/sec. The more reactive element Po, on the other hand, shows evidence of rapid in-situ scavenging. In filtered seawater,210Po is deficient, on the average, by ca. 10% relative to210Pb; a corresponding enrichment is found in the particulate phase. Total inventories of210Pb and210Po over the entire water column, however, show no significant departure from secular equilibrium.