Distribution of 236 U in the U.S. GEOTRACES Eastern Pacific Zonal Transect and its use as a water mass tracer

M. Villa-Alfageme, E. Chamizo, T. C. Kenna, M. López-Lora, N. Casacuberta, C. Chang, P. Masqué, M. Christl

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14 Citations (Scopus)


We report dissolved concentrations of the long-lived radioisotope 236 U measured in the water column along the 2013 US GEOTRACES Eastern Pacific Zonal Transect (GP16). This transect followed a 10–15°S line from Manta, Ecuador, to Papeete, Haiti, French Polynesia, crossing the southern East Pacific Rise, intercepting one of the largest hydrothermal plumes as well as a productivity gradient, which includes the upwelling zone and associated low oxygen waters offshore from Peru and the oligotrophic sub-tropical gyre. Accelerator Mass Spectrometry was used to measure dissolved seawater 236 U concentrations as low as 1 × 10 3 atom kg −1 , which are among the lowest levels reported to date. Differences in upper water column 236 U distributions from east to west are a result of variable contributions from different surface and intermediate waters encountered along the transect. The distribution of 236 U, both in depth and geographically, provides complementary information to that obtained from Δ 14 C and helium isotopes, demonstrating that 236 U concentrations are diagnostic in the identification of and contributions from the different deep and bottom water masses encountered along the EPZT (Jenkins et al., 2017). For example, we observe minimum 236 U concentrations along the EPZT between 2000 and 3000 m that are consistent with contributions attributed to Pacific Deep Water. We also observe increases in 236 U below 3000 m at the eastern and western termini of the EPZT. This is consistent with contributions associated with Antarctic Bottom Water and Lower Circumpolar Deep Water. Our results indicate that 236 U may be used in conjunction with Δ 14 C and 3 He isotopes as an additional tool with which to identify and resolve contributions from different water masses in the Pacific Ocean. This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

Original languageEnglish
Pages (from-to)44-57
Number of pages14
JournalChemical Geology
Publication statusPublished - 5 Jul 2019


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