Trace elements in marine biogenic carbonates: analysis and application to past ocean chemistry

Trace elements in marine biogenic carbonates may be used as proxies for past ocean<br/>chemistry provided that there is an established relationship between the trace element<br/>proxy and a parameter of interest, this relationship is preserved within biogenic<br/>carbonate, and the trace element can be determined sufficiently accurately. Successful<br/>application of any trace element proxy requires both development of the analytical<br/>methodology to ensure accurate data with the necessary sensitivity, and an<br/>understanding of the relationship between proxy and seawater chemistry.<br/>Herein I develop methods for the determination of Mg/Ca, Sr/Ca and Cd/Ca in<br/>planktonic foraminiferal calcite, using inductively coupled plasma optical emission<br/>spectrophotometry and isotope dilution thermal ionisation mass spectrometry, and<br/>propose a potential reference material for Mg/Ca in foraminiferal calcite. The developed<br/>techniques are applied to an investigation of the Mg/Ca temperature proxy over<br/>Chatham Rise in the Southwest Pacific Ocean and a calibration study of the partition<br/>coefficient, DCd, for cadmium incorporation into planktonic foraminifera.<br/>Comparisons of planktonic foraminiferal Mg/Ca, shell weight and oxygen<br/>isotope records from sites north and south of the Subtropical Front on Chatham Rise,<br/>demonstrate the effects of hydrography, foraminiferal habitat and dissolution as controls<br/>on Mg/Ca. Determinations of Cd/Ca in seven species of planktonic foraminifera<br/>confirm that the dominant controls on Cd/Ca are foraminiferal habitat and hydrography,<br/>with only a minor influence of post depositional dissolution. The major uncertainty in<br/>determination of DCd from core top samples comes from uncertainty in estimation of the<br/>depth distribution and seasons of calcification of planktonic foraminifera.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Greaves, Mervyn John