A Radionuclide Study of the Clyde Sea Area

MacKenzie, Angus Buchanan (1977) A Radionuclide Study of the Clyde Sea Area. PhD thesis, University of Glasgow.

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Abstract

This thesis presents the sampling and analytical procedures developed and the results obtained in a survey of the concentrations of 134Cs, 137Cs, 226Ra and 228Ra in the waters and sediments of the northern section of the Clyde Sea Area. The suitability of these nuclides as tracers of coastal marine processes is discussed and the results are applied to the estimation of water residence times and mixing rates and to the patterns of sedimentation in the area. 226Ra concentrations are determined both by preconcentration from 60 l samples and by direct analyses of 20 l samples, emanation and a counting of 222 Rn being used in both cases. 228Ra assay is performed by non-quantitative extraction of radium from more than 1000 l of sea water onto manganese dioxide impregnated acrylic fibre. The 228 Ra/ Ra activity ratio of the extracted radium is determined and the Ra concentration derived by comparison with the previously 226 determined Ra concentration. 134 Cs and 137 Cs concentrations are measured by extraction of caesium from 101 samples of sea water onto the inorganic ion exchanger potassium hexocyanocobalt (11) ferrate (11) (KCFC). Radiocaesium determination is achieved by direct gamma-ray spectrometric analysis of the ion exchange column. The dominant input of radiocaesium to the Clyde Sea Area is demonstrated to be the effluent from the Windscale nuclear fuel reprocessing facility in Cumbria. Matching of maxima in 137Cs concentrations with the Windscale output and with reported values for the North Channel indicates a water transit time of about 3 months for movement from the North Channel to the northern parts of the Clyde Sea Area. Caesium mass budget calculations indicate a mean water residence time of about 3.9 months for the area and homogeneous vertical profiles imply rapid vertical mixing. About 23% of the 137Cs discharged from Windscale is estimated to pass through the the Clyde Sea Area with 0.08% to 0.4% being retained in the sediments. Loch Goil is the only part of the region to exhibit a long residence time and radiocaesium data indicate that deep water renewal occurs by exchange with Loch Long water at a depth of about 20m. The transient development of a strong pycnocline below 20m leads to entrainment of the deep water and consequently increased residence times. Typical 226Ra concentrations are demonstrated to be in the range 100 - 160 dpm/1000 l while 226Ra/226Ra ratios are normally about 1.5. This enrichment relative to Atlantic concentrations is attributed to diffusion from sediments since river input is shown to supply only 226 about 1% of the Ra in the area. Despite the fact that diffusion of radium from sediments is the major input, the biological silicate cycle is demonstrated to exert a controlling influence on the Ra concentrations in Loch Goil. The complex behaviour of radium thus demonstrated means that evaluation of water mixing processes is virtually impassible on the basis of radium measurements alone. Both radium and radiocaesiurn are shown to exhibit conservative behaviour over the salinity range 0 to 32%. encountered in the estuary. Re226 and 134Cs/137Cs analyses of sediment cores reveal that neither radium nor radiocaesium can be used to establish a sediment chronology in this environment but that both can be used to indicate patterns of sediment accumulation with mixing depths of 4cm and more than 10cm being defined for Loch Goil and Gareloch respectively. The 134Cs/137Cs ratio is also shown to be very useful in assessing the efficiency of recovery of surface sediment. The enrichment of 137Cs in Gareloch sediment relative to ambient water concentrations is found to be about 3 times greater than that for Loch Goil. A difference in particulate flux is postulated as a possible reason for this variation. Anomalously high Ra concentrations are reported for the top 10cm of Loch Goil, with no obvious cause being apparent from the available information.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Chemical oceanography, Nuclear chemistry
Date of Award: 1977
Depositing User: Enlighten Team
Unique ID: glathesis:1977-78748
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:56
Last Modified: 30 Jan 2020 14:56
URI: http://theses.gla.ac.uk/id/eprint/78748

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