A 40-year marine record of 137Cs and 99Tc transported into the Danish Straits: Significance for oceanic tracer studies. (April 2020)

• Record Type: Journal Article
• Authors: Qiao, Jixin; Andersson, Kasper; Nielsen, Sven
• Is Part Of: Chemosphere. Volume 244(2020)
• Publication Date: 2020-04
• Subjects: 137Cs -- 99Tc -- Temporal evolution -- Transport -- Marine environment -- Tracer studies; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2019.125595
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: This work reports comprehensive time-series datasets for 137 Cs and 99 Tc in marine samples from the Danish Straits over the past 40 years, where dynamic inputs from the two European nuclear reprocessing plants Sellafield (SF) and La Hague (LH) and Chernobyl accident are clearly archived. Distinct seasonal variations between 137 Cs and 99 Tc are observed in Fucus vesiculosus ( F. vesiculosus ), which needs to be taken into account when using F. vesiculosus as a bio-monitor to represent the concentration of radionuclides in seawater. Comparable transfer factor (TF) for 99 Tc from SF to Kattegat between our calculation and earlier studies indicates a relatively steady water mass transport over the past decades. Three distinct events are observed in the temporal evolution of 99 Tc/ 137 Cs activity ratio in F. vesiculosu with the first event corresponding with the increased 99 Tc discharge from SF, while the other two are very likely related to the major Baltic inflow (MBI) events. The correlation between the 99 Tc/ 137 Cs activity ratio and salinity fits well into the binary mixing line with the North Sea (NS) and the Baltic Sea (BS) as end members. A model simulation indicates that water mass from NS constitutes less than 50% in the surface water and 50–100% for most locations in the bottom water of the Danish Straits. Overall observations show that 137 Cs and 99 Tc in marine samples, especially 99 Tc/ 137 Cs isotope ratios, serve as useful oceanic tracers to study different natural processes, such as water mixing and transport dynamics. Graphical abstract: Image 1 Highlights: 40-year time-series for 137 Cs and 99 Tc in Danish marine samples are reported. Seasonal variation between 137 Cs and 99 Tc in Fucus vesiculosus are different. Three distinct events are observed in the time-series of 99 Tc/ 137 Cs activity ratio. Binary mixing model fits well with 99 Tc/ 137 Cs activity ratio-salinity correlation. Time-series data of 137 Cs and 99 Tc serve as useful oceanic tracers.