Trace element cycling and fluxes in the South Indian Ocean – a contribution to GEOTRACES

我们建议应用Ra、Th和He同位素来详细测定地球上研究最少的海洋区域之一南印度洋(SIO)23°S带状剖面水柱中痕量元素(Te：Cd、Co、Cu、Fe、Mn、Mo、Ni、V、Zn)的来源、通量和汇。Re(224Ra、223Ra、228Ra、226Ra)、钍(234、232Th、)、氦(3He、4He)同位素的应用将有助于研究TES的生物地球化学循环，并鉴于一些TES是微量营养素，因此能够评估它们与表层海洋生产力以及碳和氮循环的相互作用。结合TES的测量，以Ra和234同位素作为水平和垂直通量的示踪，232Th作为尘埃输入的示踪，He同位素作为热液输入的示踪，我们将调查和量化TES从大气、大陆(主要是赞比西河)、沉积物(在陆坡上)和洋壳(印度洋海脊的热液作用)向SiO的供应途径。这项研究将基于计划于2020年7月至8月在从南非到澳大利亚的SIO的FS Sonne邮轮SO-276期间收集的样本。我们的调查将是国际协调计划GEOTRACES的一部分，并将为第二个印度洋考察计划(IIOE-2)做出贡献。这项研究的结果将对理解生态系统运行的化学环境具有全球意义。

We propose to apply isotopes of radium (Ra), thorium and helium (He) to determine in detail the sources, fluxes and sinks of trace elements (TEs: Cd, Co, Cu, Fe, Mn, Mo, Ni, V, Zn) in the water column along a 23°S zonal section in the South Indian Ocean (SIO), one of the least studied ocean regions on earth. The application of isotopes of radium (224Ra, 223Ra, 228Ra 226Ra,), thorium (234Th 232Th,), helium (3He, 4He) will facilitate the study of the biogeochemical cycles of TEs, and given that some TEs act as micronutrients, allow an assessment of their interactions with surface ocean productivity and the carbon and nitrogen cycles. Combining measurements of TEs with Ra and 234Th isotopes as tracers for horizontal and vertical fluxes, 232Th as a tracer for dust inputs, and He isotopes as a tracer for hydrothermal inputs, we will investigate and quantify the supply pathways of TEs to the SIO from the atmosphere, continent (mainly the Zambezi River), sediments (on continental slopes), and ocean crust (hydrothermalism of Indian Ocean Ridge). The study will be based on samples collected during FS Sonne cruise SO-276 scheduled for July – August 2020 in the SIO from South Africa to Australia. Our investigations will be part of the internationally coordinated program GEOTRACES and will contribute to the Second Indian Ocean Expedition Program (IIOE-2). The outcome of this study will have global significance for understanding the chemical environment in which ecosystems operate.