Controls on Dissolved Barium and Radium-226 Distributions in the Pacific Ocean Along GEOTRACES GP15

IF 5.4 2区 地球科学 Q1 ENVIRONMENTAL SCIENCES Global Biogeochemical Cycles Pub Date : 2024-06-10 DOI:10.1029/2023GB008005
Emilie Le Roy, Matthew A. Charette, Paul B. Henderson, Alan M. Shiller, Willard S. Moore, Nathaniel Kemnitz, Douglas E. Hammond, Tristan J. Horner
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Abstract

Radium-226(226Ra) and barium (Ba) exhibit similar chemical behaviors and distributions in the marine environment, serving as valuable tracers of water masses, ocean mixing, and productivity. Despite their similar distributions, these elements originate from distinct sources and undergo disparate biogeochemical cycles, which might complicate the use of these tracers. In this study, we investigate these processes by analyzing a full-depth ocean section of 226Ra activities (T1/2 = 1,600 years) and barium concentrations obtained from samples collected along the US GEOTRACES GP15 Pacific Meridional Transect during September–November 2018, spanning from Alaska to Tahiti. We find that surface waters possess low levels of 226Ra and Ba due to export of sinking particulates, surpassing inputs from the continental margins. In contrast, deep waters have higher 226Ra activities and Ba concentrations due to inputs from particle regeneration and sedimentary sources, with 226Ra inputs primarily resulting from the decay of 230Th in sediments. Further, dissolved 226Ra and Ba exhibit a strong correlation along the GP15 section. To elucidate the drivers of the correlation, we used a water mass analysis, enabling us to quantify the influence of water mass mixing relative to non-conservative processes. While a significant fraction of each element's distribution can be explained by conservative mixing, a considerable fraction cannot. The balance is driven using non-conservative processes, such as sedimentary, rivers, or hydrothermal inputs, uptake and export by particles, and particle remineralization. Our study demonstrates the utility of 226Ra and Ba as valuable biogeochemical tracers for understanding ocean processes, while shedding light on conservative and myriad non-conservative processes that shape their respective distributions.

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GEOTRACES GP15沿线太平洋溶解钡和镭-226分布的控制因素
镭-226(226Ra)和钡(Ba)在海洋环境中表现出相似的化学行为和分布,是水团、海洋混合和生产力的重要示踪剂。尽管这两种元素的分布相似,但它们的来源不同,经历的生物地球化学循环也不同,这可能会使这些示踪剂的使用复杂化。在本研究中,我们通过分析全深度海洋断面的 226Ra 活动(T1/2 = 1,600 年)和钡浓度来研究这些过程,226Ra 活动和钡浓度取自 2018 年 9 月至 11 月期间沿美国 GEOTRACES GP15 太平洋经向横断面采集的样本,横跨阿拉斯加至塔希提岛。我们发现,由于下沉微粒的输出,表层水域的 226Ra 和 Ba 含量较低,超过了大陆边缘的输入。相比之下,深层水域的 226Ra 活性和钡浓度较高,原因是颗粒再生和沉积物来源的输入,其中 226Ra 输入主要来自沉积物中 230Th 的衰变。此外,溶解的 226Ra 和 Ba 在 GP15 断面上表现出很强的相关性。为了阐明这种相关性的驱动因素,我们采用了水质量分析方法,使我们能够量化水质量混合相对于非保守过程的影响。虽然每种元素的分布中都有很大一部分可以用保守混合来解释,但也有相当一部分无法解释。平衡是由非保守过程驱动的,如沉积、河流或热液输入、颗粒吸收和输出以及颗粒再矿化。我们的研究证明了 226Ra 和 Ba 作为有价值的生物地球化学示踪剂对了解海洋过程的作用,同时也揭示了形成它们各自分布的保守过程和无数非保守过程。
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来源期刊
Global Biogeochemical Cycles
Global Biogeochemical Cycles 环境科学-地球科学综合
CiteScore
8.90
自引率
7.70%
发文量
141
审稿时长
8-16 weeks
期刊介绍: Global Biogeochemical Cycles (GBC) features research on regional to global biogeochemical interactions, as well as more local studies that demonstrate fundamental implications for biogeochemical processing at regional or global scales. Published papers draw on a wide array of methods and knowledge and extend in time from the deep geologic past to recent historical and potential future interactions. This broad scope includes studies that elucidate human activities as interactive components of biogeochemical cycles and physical Earth Systems including climate. Authors are required to make their work accessible to a broad interdisciplinary range of scientists.
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