Studies of trace metals in shelf waters of the British Isles
Studies of trace metals in shelf waters of the British Isles
Results are presented for the distributions of a number of dissolved trace metals (Cd, Co, Cu, Mn, Ni, Pb, Zn; ancillary data were also available for reactive aluminium) during several detailed surveys of the central and western areas of the English Channel. The sampling plan was designed to give information on the importance of potential sources of metals in influencing distributions, and sampling was undertaken under contrasting seasonal conditions in order to obtain information on the effects of phytoplankton activity and water column stability on the bio-geochemical cycling of metals. Samples were collected using modified 2.5 litre Teflon-lined Go-Flo bottles deployed on Kevlar hydroline. They were filtered (Nuclepore, 0.4 μm) and acidified to ca. pH 2. Shore-based analysis for dissolved trace metals was carried out using complexation with a mixed dithiocarbamate complexant (APDC-DDDC) and solvent extraction (Freon TF), followed by back extraction into dilute nitric acid and determination by graphite furnace atomic absorption spectrophotometry. Some modifications (mehcanisation of the back extraction step, reduction in volumes of sample and reagents) were made to existing procedures, primarily to increase sample throughput. Clean handling techniques were used at all stages. Typical detection limits (3σ blank) and coefficients of variation were: Cd(0.018 nmol 1-1, 8%); Co(0.024, 5); Cu(0.47, 10); Mn(0.052, 5); Ni(0.51, 4); Pb(0.024, 5); Zn(0.35, 3). The data on these metals have been interpreted with the aid of ancillary information on salinity, concentrations of micronutrients (dissolved silicon, phosphate, nitrate), and reactive aluminium. The mixing of Atlantic Ocean surface water and freshwaters with higher concentrations of dissolved trace metals was a significant basic factor affecting the distributions of the trace metals, as shown by significant inverse correlations of each metal investigated, with salinity. The scatter shown in these relationships indicates, however, that other factors influenced the distributions, and the possible roles of atmospheric and benthic inputs, and of interactions between dissolved and particulate (including biogenic) material are considered. Concentrations of dissolved manganese increased progressively from winter to summer (2.0 ± 0.7 (mean ± 1σ) to 5.0 ± 3.0 nmol 1-1). A surface enrichment in the upper mixed layer of the western Channel, relative to deeper water, was also observed. Concentrations of dissolved cobalt also increased from winter to spring (from ≤0.02-0.50 to 0.08-0.71 nmol 1^-1), paralleling those of dissolved manganese, and then decreased into summer (to ≤0.08-0.56 nmol 1-1). The regional distribution of dissolved lead had changed by May, possibly reflecting removal by diatoms and decreased riverine inputs, although overall mean concentrations remained similar throughout the year (0.22 nmol 1-1). Concentrations of reactive aluminium decreased in response to biological activity, being related to those of dissolved silicon during spring, and to those of phosphate and nitrate during the summer, with depletion in the upper mixed layer of the stratified waters of the western Channel. Concentrations of dissolved cadmium (0.20 nmol 1-1), copper (13.2 nmol 1-1), nickel (3.8 nmol 1-1) and zinc (7.6 nmol 1-1), and their regional distributions, remained relatively uniform over the period of the cruises. This behaviour, which contrasts with the open oceanic observations (surface depletion and regeneration at depth), may be attributable to high background levels of dissolved metals, rapid recycling of metals from sedimented phytoplankton, increased riverine inputs, and rapid mixing of the water column, which prevents the integrated effects of repeated cycles of removal from the euphotic zone from developing.
University of Southampton
1988
Tappin, Alan David
(1988)
Studies of trace metals in shelf waters of the British Isles.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Results are presented for the distributions of a number of dissolved trace metals (Cd, Co, Cu, Mn, Ni, Pb, Zn; ancillary data were also available for reactive aluminium) during several detailed surveys of the central and western areas of the English Channel. The sampling plan was designed to give information on the importance of potential sources of metals in influencing distributions, and sampling was undertaken under contrasting seasonal conditions in order to obtain information on the effects of phytoplankton activity and water column stability on the bio-geochemical cycling of metals. Samples were collected using modified 2.5 litre Teflon-lined Go-Flo bottles deployed on Kevlar hydroline. They were filtered (Nuclepore, 0.4 μm) and acidified to ca. pH 2. Shore-based analysis for dissolved trace metals was carried out using complexation with a mixed dithiocarbamate complexant (APDC-DDDC) and solvent extraction (Freon TF), followed by back extraction into dilute nitric acid and determination by graphite furnace atomic absorption spectrophotometry. Some modifications (mehcanisation of the back extraction step, reduction in volumes of sample and reagents) were made to existing procedures, primarily to increase sample throughput. Clean handling techniques were used at all stages. Typical detection limits (3σ blank) and coefficients of variation were: Cd(0.018 nmol 1-1, 8%); Co(0.024, 5); Cu(0.47, 10); Mn(0.052, 5); Ni(0.51, 4); Pb(0.024, 5); Zn(0.35, 3). The data on these metals have been interpreted with the aid of ancillary information on salinity, concentrations of micronutrients (dissolved silicon, phosphate, nitrate), and reactive aluminium. The mixing of Atlantic Ocean surface water and freshwaters with higher concentrations of dissolved trace metals was a significant basic factor affecting the distributions of the trace metals, as shown by significant inverse correlations of each metal investigated, with salinity. The scatter shown in these relationships indicates, however, that other factors influenced the distributions, and the possible roles of atmospheric and benthic inputs, and of interactions between dissolved and particulate (including biogenic) material are considered. Concentrations of dissolved manganese increased progressively from winter to summer (2.0 ± 0.7 (mean ± 1σ) to 5.0 ± 3.0 nmol 1-1). A surface enrichment in the upper mixed layer of the western Channel, relative to deeper water, was also observed. Concentrations of dissolved cobalt also increased from winter to spring (from ≤0.02-0.50 to 0.08-0.71 nmol 1^-1), paralleling those of dissolved manganese, and then decreased into summer (to ≤0.08-0.56 nmol 1-1). The regional distribution of dissolved lead had changed by May, possibly reflecting removal by diatoms and decreased riverine inputs, although overall mean concentrations remained similar throughout the year (0.22 nmol 1-1). Concentrations of reactive aluminium decreased in response to biological activity, being related to those of dissolved silicon during spring, and to those of phosphate and nitrate during the summer, with depletion in the upper mixed layer of the stratified waters of the western Channel. Concentrations of dissolved cadmium (0.20 nmol 1-1), copper (13.2 nmol 1-1), nickel (3.8 nmol 1-1) and zinc (7.6 nmol 1-1), and their regional distributions, remained relatively uniform over the period of the cruises. This behaviour, which contrasts with the open oceanic observations (surface depletion and regeneration at depth), may be attributable to high background levels of dissolved metals, rapid recycling of metals from sedimented phytoplankton, increased riverine inputs, and rapid mixing of the water column, which prevents the integrated effects of repeated cycles of removal from the euphotic zone from developing.
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Published date: 1988
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Local EPrints ID: 461375
URI: http://eprints.soton.ac.uk/id/eprint/461375
PURE UUID: 93dd67be-9af0-4429-b823-3beb15113463
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Date deposited: 04 Jul 2022 18:45
Last modified: 04 Jul 2022 18:45
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Author:
Alan David Tappin
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