Penultimate deglacial warming across the Mediterranean Sea revealed by clumped isotopes in foraminifera

L Rodríguez-Sanz,D Heslop,A Fernandez,G Marino,K M Grant,I A Müller,S M Bernasconi,E J Rohling

doi:10.1038/s41598-017-16528-6

L Rodríguez-Sanz, D Heslop + Show 6 more

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https://doi.org/10.1038/s41598-017-16528-6

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Abstract

The variability of seawater temperature through time is a critical measure of climate change, yet its reconstruction remains problematic in many regions. Mg/Ca and oxygen isotope (δ18OC) measurements in foraminiferal carbonate shells can be combined to reconstruct seawater temperature and δ18O (δ18OSW). The latter is a measure of changes in local hydrology (e.g., precipitation/evaporation, freshwater inputs) and global ice volume. But diagenetic processes may affect foraminiferal Mg/Ca. This restricts its potential in many places, including the Mediterranean Sea, a strategic region for deciphering global climate and sea-level changes. High alkalinity/salinity conditions especially bias Mg/Ca temperatures in the eastern Mediterranean (eMed). Here we advance the understanding of both western Mediterranean (wMed) and eMed hydrographic variability through the penultimate glacial termination (TII) and last interglacial, by applying the clumped isotope (Δ47) paleothermometer to planktic foraminifera with a novel data-processing approach. Results suggest that North Atlantic cooling during Heinrich stadial 11 (HS11) affected surface-water temperatures much more in the wMed (during winter/spring) than in the eMed (during summer). The method’s paired Δ47 and δ18OC data also portray δ18OSW. These records reveal a clear HS11 freshwater signal, which attenuated toward the eMed, and also that last interglacial surface warming in the eMed was strongly amplified by water-column stratification during the deposition of the organic-rich (sapropel) interval known as S5.

Highlights

The variability of seawater temperature through time is a critical measure of climate change, yet its reconstruction remains problematic in many regions
The method’s paired Δ47 and δ18OC data portray δ18OSW. These records reveal a clear Heinrich stadial 11 (HS11) freshwater signal, which attenuated toward the eMed, and that last interglacial surface warming in the eMed was strongly amplified by watercolumn stratification during the deposition of the organic-rich interval known as Sapropel 5 (S5)
We generate a Δ47-temperature record using the traditional binning method that calculates weighted averages for ~10 Δ47-replicates that are clustered a-priori on the basis that they come from the same or close-neighbour samples (Methods). This gives a Δ47-temperature record (Fig. 2c, dots) of very low resolution, which broadly depicts cooling associated with HS11 and subsequent warming into the last interglacial period

Summary

Introduction

The variability of seawater temperature through time is a critical measure of climate change, yet its reconstruction remains problematic in many regions. Sedimentary sequences from the Mediterranean Sea are excellent paleoclimate archives to resolve outstanding questions on Earth’s climate system, due to a unique understanding of terrestrial, oceanic, and atmospheric interactions in the basin[1,2,3,4] This has allowed (i) long term records of sea-level changes to be generated by exploiting the sensitivity of the seawater oxygen composition (δ18OSW, reflected in the oxygen stable isotope records of planktic foraminifera, δ18OC) to global sea-level variations[5], and (ii) marine sediment records to be placed on absolute chronologies by using nearby speleotherm records[2,6]. The foraminiferal Mg/Ca method, which allows simultaneous reconstruction of temperature and δ18OSW using the same signal carrier[10], is compromised under high alkalinity/salinity conditions, such as those in the eMed[11] where conventional foraminiferal analyses are problematic[12,13]

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