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

本文拟应用镭（Ra）、钍（钍）和氦（He）同位素详细测定南印度洋（SIO） 23°S纬向剖面水柱中微量元素（TEs: Cd、Co、Cu、Fe、Mn、Mo、Ni、V、Zn）的源、通量和汇。镭（224Ra, 223Ra, 228Ra 226Ra,），钍（234 - 232Th,），氦（3He, 4He）同位素的应用将促进TEs生物地球化学循环的研究，并且考虑到一些TEs作为微量营养素，可以评估它们与海洋表面生产力和碳氮循环的相互作用。结合以Ra和234同位素为水平和垂直通量示踪剂的TEs测量，以232Th为尘埃输入示踪剂的TEs测量，以及以He同位素为热液输入示踪剂的TEs测量，我们将研究并量化来自大气、大陆（主要是Zambezi河）、沉积物（大陆斜坡）和海洋地壳（印度洋脊的热液作用）的TEs向SIO的供应途径。该研究将基于计划于2020年7月至8月在南非至澳大利亚的SIO进行的FS Sonne巡航SO-276期间收集的样本。我们的调查将成为国际协调计划GEOTRACES的一部分，并将为第二次印度洋考察计划（IIOE-2）做出贡献。这项研究的结果将对理解生态系统运作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.