研究人员展示了从赤道和北太平洋高生产力区域下降的富含粒子的“幕”，提供了可溶铅(Pb)可逆清除的理想化例证。横跨太平洋中部的可溶铅同位素比率的经向剖面显示，在粒子浓度足够高的地方，例如在粒子幕内，人为表层溶解铅同位素比率向深海的垂直迁移表现为柱状同位素异常。这一效应的模型表明，在富含颗粒的水域中，可逆的清除作用使得来自表层的人为铅同位素比值，能够在足够快的时间尺度上穿透古老的深水，从而克服深水铅同位素比值沿深海等密度线的水平混合。
据悉，几十年来，人们已经很好地确定了金属钍的可逆清除，即溶解的金属在下沉颗粒上交换并由此转移到更深深度的海洋学过程。与非吸附性金属相比，可逆清除既深化了吸附性元素的元素分布，又缩短了它们在海洋中的海洋停留时间，并且清除最终通过沉积作用从海洋中祛除元素。因此，了解哪些金属在什么条件下进行可逆清除是很重要的。最近，包括铅、铁、铜和锌在内的一系列金属的全球生物地球化学模型中调用了可逆清除，以使得模型数据符合对海洋溶解金属分布的观察。尽管如此，在溶解金属的海洋剖面中，可逆清除的影响仍然难以显现，也难以与生物再生等其他过程区分开来。
附：英文原文
Title: Isotopes illustrate vertical transport of anthropogenic Pb by reversible scavenging within Pacific Ocean particle veils
Author: Lanning, Nathan T., Jiang, Shuo, Amaral, Vinicius J., Mateos, Katherine, Steffen, Janelle M., Lam, Phoebe J., Boyle, Edward A., Fitzsimmons, Jessica N.
Issue&Volume: 2023-5-30
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.
DOI: 10.1073/pnas.2219688120
Source: https://www.pnas.org/doi/10.1073/pnas.2219688120