238U removal and accumulation in Concepción bay sediments, Chile

Activity profiles of 234U, 238U and 210Pb, as well as the 234U/238U ratio, and 210Pb xs radiochemical parameters and macrobenthic abundance in sediments were measured and calculated at different times during a year (1991), along a transect between the head and the mouth of Concepción Bay, Chile. Thi...

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Autores principales:	Farías,Laura, Salamanca,Marco A., Chuecas,Lizandro A.
Lenguaje:	English
Publicado:	Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2000
Materias:	U removal and accumulation bacterial sulphate reduction and bioperturbation Coastal upwelling Central Chile
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082000000200005
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spelling	oai:scielo:S0716-020820000002000052001-03-26238U removal and accumulation in Concepción bay sediments, ChileFarías,LauraSalamanca,Marco A.Chuecas,Lizandro A. U removal and accumulation bacterial sulphate reduction and bioperturbation Coastal upwelling Central Chile Activity profiles of 234U, 238U and 210Pb, as well as the 234U/238U ratio, and 210Pb xs radiochemical parameters and macrobenthic abundance in sediments were measured and calculated at different times during a year (1991), along a transect between the head and the mouth of Concepción Bay, Chile. This bay is a semi-enclosed shallow embayment with a strong seasonality in its hydrographic and biological characteristics due to wind driven upwelling. Upwelling of oxygen-poor and nutrient-rich water occurs and organic detritus reaches the seabed, creating a sub-oxic and anoxic environment during, at least, 57% of the year. 238U and 234U activities in the sediments show a gradual increase from 1.57 to 6.07 dpm g-1 from the surface to 15 cm depth in the sediments. Under suboxic-anoxic conditions, this pattern is consistent with a reduction of U(VI) to U(IV) and its subsequent removal from pore-water. A 234U/238U ratio of 1.10 ±0.08 indicates an authigenic origen. The 238U accumulation rate and inventory show a significant increase from Station 1 (head of the bay) to Station 3 (mouth of the bay) from 348 to 794 dpm cm-2 kyr-1 and of 14 to 32 dpm cm-2, respectively. The organic-rich and highly reducing sediments also show an increase in sulphate-reduction rates, sulfur speciation and bioturbation activities of macrobenthos. These patterns suggest that the extent of U enrichment in these sediments is regulated by bacterial sulphate reduction rate and bioturbation and bioirrigation activities. The estimated 238U accumulation rates are higher than those reported for other anoxic environments, representing an important U sink in marine sediments. The geochemical behaviour of U seems to be very sensitive to the redox condition and this characteristic could become an important paleoceanographic tool to identify changes in oceanographic conditions during the last millenniuminfo:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Revista geológica de Chile v.27 n.2 20002000-12-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082000000200005en10.4067/S0716-02082000000200005
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	U removal and accumulation bacterial sulphate reduction and bioperturbation Coastal upwelling Central Chile
spellingShingle	U removal and accumulation bacterial sulphate reduction and bioperturbation Coastal upwelling Central Chile Farías,Laura Salamanca,Marco A. Chuecas,Lizandro A. 238U removal and accumulation in Concepción bay sediments, Chile
description	Activity profiles of 234U, 238U and 210Pb, as well as the 234U/238U ratio, and 210Pb xs radiochemical parameters and macrobenthic abundance in sediments were measured and calculated at different times during a year (1991), along a transect between the head and the mouth of Concepción Bay, Chile. This bay is a semi-enclosed shallow embayment with a strong seasonality in its hydrographic and biological characteristics due to wind driven upwelling. Upwelling of oxygen-poor and nutrient-rich water occurs and organic detritus reaches the seabed, creating a sub-oxic and anoxic environment during, at least, 57% of the year. 238U and 234U activities in the sediments show a gradual increase from 1.57 to 6.07 dpm g-1 from the surface to 15 cm depth in the sediments. Under suboxic-anoxic conditions, this pattern is consistent with a reduction of U(VI) to U(IV) and its subsequent removal from pore-water. A 234U/238U ratio of 1.10 ±0.08 indicates an authigenic origen. The 238U accumulation rate and inventory show a significant increase from Station 1 (head of the bay) to Station 3 (mouth of the bay) from 348 to 794 dpm cm-2 kyr-1 and of 14 to 32 dpm cm-2, respectively. The organic-rich and highly reducing sediments also show an increase in sulphate-reduction rates, sulfur speciation and bioturbation activities of macrobenthos. These patterns suggest that the extent of U enrichment in these sediments is regulated by bacterial sulphate reduction rate and bioturbation and bioirrigation activities. The estimated 238U accumulation rates are higher than those reported for other anoxic environments, representing an important U sink in marine sediments. The geochemical behaviour of U seems to be very sensitive to the redox condition and this characteristic could become an important paleoceanographic tool to identify changes in oceanographic conditions during the last millennium
author	Farías,Laura Salamanca,Marco A. Chuecas,Lizandro A.
author_facet	Farías,Laura Salamanca,Marco A. Chuecas,Lizandro A.
author_sort	Farías,Laura
title	238U removal and accumulation in Concepción bay sediments, Chile
title_short	238U removal and accumulation in Concepción bay sediments, Chile
title_full	238U removal and accumulation in Concepción bay sediments, Chile
title_fullStr	238U removal and accumulation in Concepción bay sediments, Chile
title_full_unstemmed	238U removal and accumulation in Concepción bay sediments, Chile
title_sort	238u removal and accumulation in concepción bay sediments, chile
publisher	Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate	2000
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082000000200005
work_keys_str_mv	AT fariaslaura 238uremovalandaccumulationinconcepcionbaysedimentschile AT salamancamarcoa 238uremovalandaccumulationinconcepcionbaysedimentschile AT chuecaslizandroa 238uremovalandaccumulationinconcepcionbaysedimentschile
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238U removal and accumulation in Concepción bay sediments, Chile

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