Abstract
Precisely targeted measurements of trace elements using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) reveal inter-chamber heterogeneities in specimens of the planktic foraminifer Trilobatus (Globigerinoides) sacculifer. We find that Mg/Ca ratios in the final growth chamber are generally lower compared to previous growth chambers, but final chamber Mg/Ca is elevated in one of thirteen sample intervals. Differences in distributions of Mg/Ca values from separate growth chambers are observed, occurring most often at lower Mg/Ca values, suggesting that single-chamber measurements may not be reflective of the specimen’s integrated Mg/Ca. We compared LA-ICPMS Mg/Ca values to paired, same-individual Mg/Ca measured via inductively coupled plasma optical emission spectrometry (ICP-OES) to assess their correspondence. Paired LA-ICPMS and ICP-OES Mg/Ca show a maximum correlation coefficient of R = 0.92 (p < 0.05) achieved by applying a weighted average of the last and penultimate growth chambers. Population distributions of paired Mg/Ca values are identical under this weighting. These findings demonstrate that multi-chamber LA-ICPMS measurements can approximate entire specimen Mg/Ca, and is thus representative of the integrated conditions experienced during the specimen’s lifespan. This correspondence between LA-ICPMS and ICP-OES data links these methods and demonstrates that both generate Mg/Ca values suitable for individual foraminifera palaeoceanographic reconstructions.
Highlights
Mg/Ca ratios from individual foraminifera have been used to asses oceanic conditions and variability, including assessment of changes in interannual variability associated with the El Niño Southern Oscillation (ENSO)[7,8,9,10,16,20,21]
In this study we examine Mg/Ca variability within shells of the planktic foraminifer Trilobatus (Globigerinoides) sacculifer (19, Brady 1877) using LA-ICPMS, and quantify the relationship between Mg/Ca values obtained from LA-ICPMS and from inductively-coupled plasma optical emission spectrometry (ICP-OES) on the same foraminifera specimens
The small shell volume sampled by LA-ICPMS could systematically differ from the whole shell, while solution cleaning methods for ICP-MS could remove shell material that is included in LA-ICPMS analysis
Summary
Mg/Ca ratios from individual foraminifera have been used to asses oceanic conditions and variability, including assessment of changes in interannual variability associated with the El Niño Southern Oscillation (ENSO)[7,8,9,10,16,20,21]. The shell chemistry of each foraminifer reflects the ocean conditions it experienced during its 2–4 week life s pan[22]. These ~ monthly ‘snapshots’ generate a distribution of conditions that occurred during the duration of an accumulating sediment interval. Studies using Mg/Ca from individual foraminifera analysis have used both ICP-MS23, ICP-OES16, and LA-ICPMS7–9,11 analytical techniques. While differing analytical methods may provide similar population mean Mg/Ca results, this is no guarantee that the population distributions are similar. The small shell volume sampled by LA-ICPMS could systematically differ from the whole shell, while solution cleaning methods for ICP-MS could remove shell material that is included in LA-ICPMS analysis. The degree to which analytical technique may influence the Mg/Ca values, and existing Mg/Ca temperature calibrations, has not been evaluated on individual foraminifera
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