A multi basin calibration of the Mg/Ca paleo-thermometer corrected for habitat depth and test dissolution
Abstract
One of the biggest drawbacks of foraminifer-based Mg/Ca paleothermometry is that different calibration equations produce largely varying temperature estimates from the same Mg/Ca data. We combine new Mg/Ca data from Atlantic core tops with those previously published from the eastern and western tropical Pacific and other Atlantic core tops to derive multi-basin calibration equations for the Mg/Ca-temperature relationship from tests of five planktonic foraminifer species: Globigerinoides ruber, Globigerinoides sacculifer, Pulleniatina obliquiloculata, Globorotalia menardii, and Neogloboquadrina dutertrei. Our equations are calibrated with δ18O-based habitat depth temperatures for each species and account for test dissolution using percent calcite dissolved estimates from the G. menardii fragmentation index (MFI). We find that the effect of dissolution is less on the mixed layer dwellers (G. ruber and G. sacculifer) and more easily quantifiable on the deeper dwellers. Furthermore, the U/Ca ratio of deeper dwellers has a quantifiable relationship with MFI-based percent calcite dissolved. To expand our dataset, we examined Mg/Ca data from Globorotalia truncatulinoides, Globigerinoides conglobatus, G. menardii and Globorotalia hirsuta from the Rio Grande Rise where habitat temperatures are minimally variable among core tops but dissolution increases greatly with water depth. We find that Mg/Ca values from G. truncatulinoides and G. conglobatus diminish predictably with increasing dissolution (based on MFI), whereas Mg/Ca values from G. hirsuta do not. Based on our multi-basin dataset and new calibration equations, we infer that G. ruber, G. sacculifer and G. hirsuta must have more homogeneous test geochemistry with respect to Mg/Ca than the other species.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP12B..02M
- Keywords:
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- 0419 Biomineralization;
- BIOGEOSCIENCES;
- 0454 Isotopic composition and chemistry;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4994 Instruments and techniques;
- PALEOCEANOGRAPHY