Improving the reproducibility of stable isotope records from planktonic and benthic foraminifera

• Main Authors: Maslin, MA, Hall, MA
• Format: Report
• Language: English
• Published: UCL Environmental Change Research Centre 1997
• Subjects: Neogloboquadrina pachyderma
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10111333/1/ecrc_report_40_Maslin%20%26%20Hall_1997_foraminifera_isotope%20records_OCR.pdf; https://discovery.ucl.ac.uk/id/eprint/10111333/

Foraminiferal oxygen and carbon stable isotope measurements have become an indispensable part of palaeoceanography. It is therefore important to understand and to improve the reproducibility of these measurements. We have estimated the reproducibility of oxygen and carbon stable isotopes of the planktic foraminifera, Globigerina bulloides and Neogloboquadrina pachyderma (sinistral) and the benthic foraminifera Uvigerina peregrina. To obtain stable isotope results from planktic foraminifera with a reproducibility of better than ±0.2%0 we suggest that: (1) tests should be picked from discrete size fractions of less than ±25μrn standardised for each species and ocean, and (2) that at least 30 tests are measured per sample. Isotope measurement of individual tests of the benthic foraminifera U. peregrina heavier than 25 μg give good reproducibility. Below 25 μg both standards and measurements of individual tests show a deviation of up to 0.7%0 from the the 95% confidence limits of larger samples. This we believe is due to a memory effect in the mass spectrometer source. This effect can be reduced by allowing a longer pumping out time of at least 100 seconds between the standard and sample gas measurements. This, however, increases measurement time to 20 minutes per sample, and it can not guarantee reproducible ol3C as there are vital effects associated with growth below 25 μg.