PDF(Pubmed)
Abstract：
Reversible scavenging, the oceanographic process by which dissolved metals exchange onto and off sinking particles and are thereby transported to deeper depths, has been well established for the metal thorium for decades. Reversible scavenging both deepens the elemental distribution of adsorptive elements and shortens their oceanic residence times in the ocean compared to nonadsorptive metals, and scavenging ultimately removes elements from the ocean via sedimentation. Thus, it is important to understand which metals undergo reversible scavenging and under what conditions. Recently, reversible scavenging has been invoked in global biogeochemical models of a range of metals including lead, iron, copper, and zinc to fit modeled data to observations of oceanic dissolved metal distributions. Nonetheless, the effects of reversible scavenging remain difficult to visualize in ocean sections of dissolved metals and to distinguish from other processes such as biological regeneration. Here, we show that particle-rich \"veils\" descending from high-productivity zones in the equatorial and North Pacific provide idealized illustrations of reversible scavenging of dissolved lead (Pb). A meridional section of dissolved Pb isotope ratios across the central Pacific shows that where particle concentrations are sufficiently high, such as within particle veils, vertical transport of anthropogenic surface-dissolved Pb isotope ratios toward the deep ocean is manifested as columnar isotope anomalies. Modeling of this effect shows that reversible scavenging within particle-rich waters allows anthropogenic Pb isotope ratios from the surface to penetrate ancient deep waters on timescales sufficiently rapid to overcome horizontal mixing of deep water Pb isotope ratios along abyssal isopycnals.
摘要：
可逆清除,溶解的金属交换到下沉的颗粒上和下的海洋过程，从而被输送到更深的深度，金属钍已经确立了几十年。与非吸附金属相比，可逆清除既加深了吸附元素的元素分布，又缩短了它们在海洋中的海洋停留时间，清除最终通过沉积从海洋中去除元素。因此，重要的是要了解哪些金属经历可逆清除和在什么条件下。最近,可逆清除已在包括铅在内的一系列金属的全球生物地球化学模型中被调用，铁,铜，和锌来拟合建模数据以观测海洋溶解金属分布。尽管如此，可逆清除的影响仍然难以在溶解金属的海洋部分中可视化，也难以与生物再生等其他过程区分开来。这里,我们表明，从赤道和北太平洋的高生产力区下降的富含颗粒的“面纱”提供了可逆清除溶解铅（Pb）的理想化例证。整个太平洋中部溶解的Pb同位素比率的子午线部分表明，在粒子浓度足够高的地方，例如在粒子面纱内，人为表面溶解的Pb同位素比率向深海的垂直传输表现为柱状同位素异常。对这种效应的建模表明，在富含颗粒的水中进行可逆清除可以使地表的人为Pb同位素比在足够快的时间尺度上渗透到古代深水中，以克服深水Pb同位素比沿深海等值线的水平混合。
