The effects of temperature, salinity, and the carbonate system on Mg/Ca in Globigerinoides ruber (white): a global sediment trap calibration

William R. Gray*, Syee Weldeab, David W. Lea, Yair Rosenthal, Nicolas Gruber, Barbara Donner, Gerhard Fischer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

82 Citations (Scopus)

Abstract

The Mg/Ca of planktic foraminifera Globigerinoides ruber (white) is a widely applied proxy for tropical and sub-tropical sea-surface temperature. The accuracy with which temperature can be reconstructed depends on how accurately relationships between Mg/Ca and temperature and the multiple secondary controls on Mg/Ca are known; however, these relationships remain poorly quantified under oceanic conditions. Here, we present new calibrations based on 440 sediment trap/plankton tow samples from the Atlantic, Pacific and Indian Oceans, including 130 new samples from the Bay of Bengal/Arabian Sea and the tropical Atlantic Ocean. Our results indicate temperature, salinity and the carbonate system all significantly influence Mg/Ca in G. ruber (white). We propose two calibration models: The first model assumes pH is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.0±0.8%/°C (2σ), a salinity sensitivity of 3.3±2.2%/PSU and a pH sensitivity of −8.3±7.7%/0.1 pH units; The second model assumes carbonate ion concentration ([CO32−]) is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.7±0.8%/°C, a salinity sensitivity of 5.0±3.0%/PSU and a [CO32−] sensitivity of −0.24±0.11%/μmol kg−1. In both models, the temperature sensitivity is significantly lower than the widely-applied sensitivity of 9.0±0.6%/°C. Application of our new calibrations to down-core data from the Last Glacial Maximum, considering whole ocean changes in salinity and carbonate chemistry, indicate a cooling of 2.4±1.6°C in the tropical oceans if pH is the controlling parameter and 1.5±1.4°C if [CO32−] is the controlling parameter.

Original languageEnglish
Pages (from-to)607-620
Number of pages14
JournalEarth and Planetary Science Letters
Volume482
Early online date8 Dec 2017
DOIs
Publication statusPublished - 15 Jan 2018

Keywords

  • Carbonate chemistry
  • Mg/Ca
  • Planktic foraminifera
  • Salinity
  • SST

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