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A field-based study on variation in Mg/Ca and Sr/Ca in larger benthic foraminifera

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Title A field-based study on variation in Mg/Ca and Sr/Ca in larger benthic foraminifera
 
Creator RAJA, R
SARASWATI, PK
 
Subject element-calcium ratios
planktonic-foraminifera
paleotemperature proxy
strontium compositions
magnesium
temperature
sea
mg
thermometry
shells
larger foraminifera
mg/ca
sr/ca
paleotemperature
symbiosis.
 
Description [1] The Mg/Ca and Sr/Ca ratios of foraminifera are used as proxies of paleotemperature. Although the Mg/Ca is found to be related with temperature in planktonic foraminifera, the reliability of this proxy in benthic foraminifera has yet to be established. It is essential therefore to understand the minor elements' composition and their relation to ambient water parameters in different benthic foraminiferal species. In this study, a systematic field-based study was carried out on larger benthic foraminifera (LBF) of Okinawa ( Japan) to assess if Mg/Ca and Sr/Ca in their tests could be used as proxies of seawater temperature. Five seasonal samples were collected from the reef flat to pick live specimens of Amphistegina lessonii, Neorotalia calcar, Calcarina hispida, Calcarina gaudichaudii, Baculogypsina sphaerulata, and Marginopora kudakajimaensis. The Mg/Ca in A. lessonii was -60 mmol/mol, while in the remaining five species the values were >200 mmol/mol, substantially higher than that recorded in planktonic and smaller benthic foraminifera. Interspecies and intraspecies Mg/Ca variations were fairly large even in samples of the same season. The Sr/Ca were quite uniform ( -2 mmol/mol) across the species and seasons. The correlations between test Mg/Ca and Sr/Ca and ambient water temperature and salinity were found to be poor. The possible reasons are ( 1) the influence of biological activities, particularly the photosynthesis-respiration cycle of algal symbionts, and ( 2) masking of the true relationship due to an "averaging'' effect in whole-test analysis of species having longer a life span. In view of this it is suggested that the whole-shell Mg/Ca and Sr/Ca of LBF is not an apt proxy of paleotemperature.
 
Publisher AMER GEOPHYSICAL UNION
 
Date 2011-07-15T05:40:54Z
2011-12-26T12:49:17Z
2011-12-27T05:35:06Z
2011-07-15T05:40:54Z
2011-12-26T12:49:17Z
2011-12-27T05:35:06Z
2007
 
Type Article
 
Identifier GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 8(), -
1525-2027
http://dx.doi.org/10.1029/2006GC001478
http://dspace.library.iitb.ac.in/xmlui/handle/10054/4170
http://hdl.handle.net/10054/4170
 
Language en