First 236U data from the Arctic Ocean and use of 236U/238U and 129I/236U as a new dual tracer

• Published in: Earth and Planetary Science Letters
• Main Authors: Casacuberta, Nuria, Masqué, Pere, Henderson, Gideon, Rutgers van-der-Loeff, Michiel, Bauch, Dorothea, Vockenhuber, Christof, Daraoui, Abdelouahed, Walther, Clemens, Synal, Hans-Arno, Christl, Marcus
• Format: Text
• Language: unknown
• Published: Edith Cowan University, Research Online, Perth, Western Australia 2016
• Subjects: 129I; 236U; Arctic Ocean; GEOTRACES; Tracers; Oceanography; Radioactive tracers; Anthropogenic sources; Atlantic water; Natural backgrounds; Oceanographic tools; Surface sample; Upper water column; Iodine; Arctic; Pacific
• Online Access: https://ro.ecu.edu.au/ecuworkspost2013/1542; https://doi.org/10.1016/j.epsl.2016.02.020

The first dataset of 236U/238U in the water column of the Arctic Ocean (AO) is presented and shows the widest range of ratios reported so far in the open ocean, from (5±5) to (3840±260)×10-12. Surface samples and depth profiles were collected during two GEOTRACES expeditions in 2011-2012 and analyzed for the concentrations of 236U and 129I, with the aim of investigating whether the combination of 236U/238U and 129I/236U can be used as a new oceanographic tool in the AO. Results show that the distributions of the 236U/238U and 129I/236U atomic ratios are consistent with the different water masses in the AO. High 236U/238U and 129I/236U ratios in the upper water column (>2000×10-12 and >200, respectively) illustrate the penetration of Atlantic waters (AW) into the AO. Lower values were found in Pacific waters (PW) and deep waters of the AO. Rivers seem to represent a temporally and spatially-constrained third anthropogenic source of 236U but more data are needed to confirm this. In a simple mixing model, the combination of 236U/238U and 129I/236U reveals a high contribution (>99%) of natural background waters (pre-nuclear era) in the deep and bottom waters of the Amerasian basin, indicating an apparent water mass renewal time of >1000 years. Despite the relatively high apparent age of the Amerasian Basin deep waters, this work shows the potential of using the dual-tracer approach as a new oceanographic tool in the Arctic Ocean. © 2016 Elsevier B.V.