Uncertainties in seawater thermometry deriving from intratest and interest Mg/Ca variability in Globigerinoides ruber.

Date

2008

Authors

Sadekov, Aleksey
Eggins, Stephen
De Deckker, Patrick
Kroon, Dick

Journal Title

Journal ISSN

Volume Title

Publisher

American Geophysical Union

Abstract

Laser ablation inductively coupled plasma-mass spectrometry microanalysis of fossil and live Globigerinoides ruber from the eastern Indian Ocean reveals large variations of Mg/Ca composition both within and between individual tests from core top or plankton pump samples. Although the extent of intertest and intratest compositional variability exceeds that attributable to calcification temperature, the pooled mean Mg/Ca molar values obtained for core top samples between the equator and >30°S form a strong exponential correlation with mean annual sea surface temperature (Mg/Ca mmol/mol = 0.52 exp0.076SST°C, r2 = 0.99). The intertest Mg/Ca variability within these deep-sea core top samples is a source of significant uncertainty in Mg/Ca seawater temperature estimates and is notable for being site specific. Our results indicate that widely assumed uncertainties in Mg/Ca thermometry may be underestimated. We show that statistical power analysis can be used to evaluate the number of tests needed to achieve a target level of uncertainty on a sample by sample case. A varying bias also arises from the presence and varying mix of two morphotypes (G. ruber ruber and G. ruber pyramidalis), which have different mean Mg/Ca values. Estimated calcification temperature differences between these morphotypes range up to 5°C and are notable for correlating with the seasonal range in seawater temperature at different sites.

Description

Keywords

Keywords: calcium; fossil; inductively coupled plasma method; magnesium; mass spectrometry; morphotype; sea surface temperature; seawater; statistical analysis; Indian Ocean; Globigerinoides ruber; Pyramidalis

Citation

Source

Paleoceanography

Type

Journal article

Book Title

Entity type

Access Statement

License Rights

DOI

10.1029/2007PA001452

Restricted until

2037-12-31