Trace element cycling and fluxes in the South Indian Ocean – a contribution to GEOTRACES
Final Report Abstract
In this project we conducted detailed water column surveys on the Meteor cruise M176/2 in close vicinity to the Rainbow vent field and up to a distance of ~ 60 km. We determined the distributions of trace elements (TEs, e.g., Fe, Mn, Co, Ni, Cu, Zn, Cd, Pb, and rare earth elements) and their isotopes (Th, Ba, Fe) in the non-buoyant Rainbow hydrothermal plume. Together with noble gas data, we assessed the behaviours of trace elements and their isotopes (TEIs) during the plume dispersal and evaluated the fluxes of TEIs from the Rainbow hydrothermal field. Our data reveal that the high Fe/H2S ratio of the Rainbow vent fluid limited the precipitation of metal sulphides, and hence facilitated the long-range transport of hydrothermally sourced TEs into the North Atlantic Ocean. Specifically, dissolved Co was unexpectedly conservative during the plume dispersal, and other TEs (e.g., Fe and Mn) in the Rainbow plume followed kinetically controlled removal processes. Our Fe isotope data reveal an overlooked sedimentary contribution for TEs in hydrothermal plumes, due to the interaction between hydrothermal plumes and valley sediments during plume transport. The sediment-seawater interaction was further studied by TE distributions in sediment cores and porewater samples that were collected on the cruise. We proposed that the reaction kinetics of the studied elements with sulphide follow the order Cu>Co>Zn>Fe>Ni>>Mn, which is different than the steady state affinities of these TEs to sulphide. Our Ba isotope data indicated that hydrothermal Ba could be an isotopically light (rather than previously suggested heavy) source component of the marine Ba isotope budget. Surprisingly, shortlived 223Ra and 224Ra as well as 228Ra activities in the Rainbow plume were below the detection limit, raising the question whether Ra is removed by scavenging processes rapidly upon its release in the vent fluid or it is not released from the vent at all. We further determined the supply of TEIs to the surface ocean via atmospheric deposition and their relationships with phytoplankton community. The results indicate that a dry deposition event did not lead to any observable phytoplankton growth responses, whereas the wet deposition event led to an approximate doubling of chlorophyll a. Our bioassay experiments further confirmed that this wet deposition event led to a transition from N limitation to N–P co-limitation of phytoplankton growth. Conducting interdisciplinary work on the Rainbow hydrothermal field is challenging. However, we successfully performed the research cruise M176/2 and the following laboratory work, and gained a better understanding of the sources, behaviors, and fates of TEs in non-buoyant hydrothermal plumes emanating from slow spreading ridges. Our work could help future ocean models concerning biogeochemical cycles of TEs and their impact on the marine carbon cycle and global climate.
Publications
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ADCP current measurements (38 kHz) during RV METEOR cruise M176/2 [dataset]. PANGAEA
Achterberg E. P., Kopte R. & Galley C. G.
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ontinuous thermosalinograph oceanography along RV METEOR cruise M176/2 [dataset]. PANGAEA,
Achterberg E. P. & Schlundt M.
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Organic complexation of Ni in the hydrothermal plume of the Rainbow vent field.. Goldschmidt2022 abstracts. European Association of Geochemistry.
Fröhberg, Nico; Klose, Lukas & Koschinsky, Andrea
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Dissolved and particulate barium concentrations and isotopes in the Rainbow non-buoyant hydrothermal plume during METEOR cruise M176/2 [dataset]. PANGAEA
Zhang Z., Zhou L., Achterberg E.P. & Frank M.
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Is the Rainbow ultramafic hydrothermal system a poor source of radium isotopes to the Atlantic Ocean?. Goldschmidt2023 abstracts. European Association of Geochemistry.
Vieira, Lúcia; Steiner, Zvi; Scholten, Jan; Beck, Aaron & Achterberg, Eric
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Multibeam bathymetry raw data (Kongsberg EM 122 entire dataset) of RV METEOR during cruise M176/2 [dataset]. PANGAEA
Achterberg E. P. & Wölfl A.-C.
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Noble gas (helium and neon) measured on water samples from stainless steel CTD during METEOR M176/2 cruise. [dataset]
Chen X.-G. & Achterberg E. P.
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Phytoplankton community response to episodic wet and dry aerosol deposition in the subtropical North Atlantic. Limnology and Oceanography, 68(9), 2126-2140.
Yuan, Zhongwei; Achterberg, Eric P.; Engel, Anja; Wen, Zuozhu; Zhou, Linbin; Zhu, Xunchi; Dai, Minhan & Browning, Thomas J.
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Regulation of hydrothermal vent contribution to ocean chemistry by hydrothermally influenced sediments, the Rainbow field case study. Goldschmidt2023 abstracts. European Association of Geochemistry.
Steiner, Zvi; Zhang, Zhouling; Galley, Christopher; Zhou, Linbin; Shalev, Netta; Glock, Nicolaas; Chen, Xue-Gang & Achterberg, Eric
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Introduction of isotopically light barium from the Rainbow hydrothermal system into the deep Atlantic Ocean. Earth and Planetary Science Letters, 625, 118476.
Zhang, Zhouling; Zhou, Linbin; Chen, Xue-Gang; Achterberg, Eric P.; Yu, Yang; Hathorne, Ed; Steiner, Zvi; Siebert, Christopher & Frank, Martin
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Switches between nitrogen limitation and nitrogen–phosphorus co‐limitation in the subtropical North Atlantic Ocean. Limnology and Oceanography, 69(4), 1005-1013.
Yuan, Zhongwei; Achterberg, Eric P.; Engel, Anja; Dai, Minhan & Browning, Thomas J.
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Change in biodiversity and abundance of benthic foraminifera with distance from the Rainbow hydrothermal vent field, Mid-Atlantic Ridge. Journal of Micropalaeontology, 44(2), 193-211.
Krüger, Hannah; Schmiedl, Gerhard; Steiner, Zvi; Zhang, Zhouling; Achterberg, Eric P. & Glock, Nicolaas
