Anthropogenic ²³⁶U and ²³³U in the Baltic Sea: Distributions, source terms, and budgets

Author(s)

Mu Lin, Jixin Qiao, Xiaolin Hou, Peter Steier, Robin Golser, Martin Schmidt, Olaf Dellwig, Martin Hansson, Örjan Bäck, Vesa-Pekka Vartti, Colin Stedmon, Jun She, Jens Murawski, Ala Aldahan, Stefanie A.K. Schmied

Abstract

The Baltic Sea receives substantial amounts of hazardous substances and nutrients, which accumulate for decades and persistently impair the Baltic ecosystems. With long half-lives and high solubility, anthropogenic uranium isotopes (236U and 233U) are ideal tracers to depict the ocean dynamics in the Baltic Sea and the associated impacts on the fates of contaminants. However, their applications in the Baltic Sea are hampered by the inadequate source-term information. This study reports the first three-dimensional distributions of 236U and 233U in the Baltic Sea (2018–2019) and the first long-term hindcast simulation for reprocessing-derived 236U dispersion in the North-Baltic Sea (1971–2018). Using 233U/236U fingerprints, we distinguish 236U from the nuclear weapon testing and civil nuclear industries, which have comparable contributions (142 ± 13 and 174 ± 40 g) to the 236U inventory in modern Baltic seawater. Budget calculations for 236U inputs since the 1950s indicate that, the major 236U sources in the Baltic Sea are the atmospheric fallouts (∼1.35 kg) and discharges from nuclear reprocessing plants (> 211 g), and there is a continuous sink of 236U to the anoxic sediments (589 ± 43 g). Our findings also indicate that the limited water renewal endows the Baltic Sea a strong "memory effect" retaining aged 236U signals, and the previously unknown 236U in the Baltic Sea is likely attributed to the retention of the mid-1990s' discharges from the nuclear reprocessing plants. Our preliminary results demonstrate the power of 236U-129I dual-tracer in investigating water-mass mixing and estimating water age in the Baltic Sea, and this work provides fundamental knowledge for future 236U tracer studies in the Baltic Sea.

Organisation(s)

Isotope Physics

External organisation(s)

Technical University of Denmark (DTU), Leibniz-Institut für Ostseeforschung, Swedish Meteorological and Hydrological Institute, Radiation and Nuclear Safety Authority, Danish Meteorological Institute (DMI), United Arab Emirates University, Federal Maritime and Hydrographic Agency of Germany

Journal

Water Research

Volume

210

No. of pages

12

ISSN

0043-1354

DOI

https://doi.org/10.1016/j.watres.2021.117987

Publication date

12-2021

Peer reviewed

Yes

Austrian Fields of Science 2012

103014 Nuclear physics, 103037 Environmental physics, 105206 Meteorology

Keywords

ASJC Scopus subject areas

Water Science and Technology, Ecological Modelling, Pollution, Waste Management and Disposal, Environmental Engineering, Civil and Structural Engineering

Portal url

https://ucris.univie.ac.at/portal/en/publications/anthropogenic-236u-and-233u-in-the-baltic-seadistributions-source-terms-and-budgets(958e7aed-2cb7-4795-aa9c-60c0c1980386).html