A robust calibration of the clumped isotopes to temperature relationship for foraminifers

N Meinicke,S.L Ho,B Hannisdal,D Nürnberg,A Tripati,R Schiebel,A.N Meckler

doi:10.1016/j.gca.2019.11.022

Abstract

The clumped isotope (Δ47) proxy is a promising geochemical tool to reconstruct past ocean temperatures far back in time and in unknown settings, due to its unique thermodynamic basis that renders it independent from other environmental factors like seawater composition. Although previously hampered by large sample-size requirements, recent methodological advances have made the paleoceanographic application of Δ47 on small (<5 mg) foraminifer samples possible.Previous studies show a reasonable match between Δ47 calibrations based on synthetic carbonate and various species of planktonic foraminifers. However, studies performed before recent methodological advances were based on relatively few species and data treatment that is now outdated. To overcome these limitations and elucidate species-specific effects, we analyzed 14 species of planktonic foraminifers in sediment surface samples from 13 sites, covering a growth temperature range of ∼0–28 °C. We selected mixed layer-dwelling and deep-dwelling species from a wide range of ocean settings to evaluate the feasibility of temperature reconstructions for different water depths. Various techniques to estimate foraminifer calcification temperatures were tested in order to assess their effects on the calibration and to find the most suitable approach.Results from this study generally confirm previous findings that there are no species-specific effects on the Δ47-temperature relationship in planktonic foraminifers, with one possible exception. Various morphotypes of Globigerinoides ruber were found to often deviate from the general trend determined for planktonic foraminifers.Our data are in excellent agreement with a recent foraminifer calibration study that was performed with a different analytical setup, as well as with a calibration based exclusively on benthic foraminifers. A combined, methodologically homogenized dataset also reveals very good agreement with an inorganic calibration based on travertines. Our findings highlight the potential of the Δ47 paleothermometer to be applied to recent and extinct species alike to study surface ocean temperatures as well as thermocline variability for a multitude of settings and time scales.

Highlights

The ocean is an essential part of the Earth’s climate system by storing and redistributing heat and moisture
Paper III: A multi-proxy study of changes in the Indonesian Throughflow since the Pliocene In Paper III, we present mixed layer temperature reconstructions based on paired Mg/Ca and clumped isotope analysis on planktonic foraminifera from a region just downstream of the Indonesian Throughflow, off North-West Australia
Using our new data together with a methodologically homogenized dataset of recently published clumped isotope data measured on foraminifera (Breitenbach et al, 2018; Peral et al, 2018; Piasecki et al, 2019), we demonstrate the reproducibility of clumped isotope analyses that are referenced to carbonate standards, irrespective of laboratory-specific measurement approaches

Summary

Introduction

The ocean is an essential part of the Earth’s climate system by storing and redistributing heat and moisture. The oceans hold information about past climate change in the sediments on the seafloor In these sediments climate proxies can be measured providing tools to decipher information about the Earth’s climate history (Emiliani, 1954). These reconstructions of past climate variability are crucial to understand mechanisms and feedbacks within Earth’s climate system because they yield time series of various environmental parameters and document their relationship to each other

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