A A A

Employee information:

Name: Juliane Steinhardt
Department: Ocean Systems Sciences (OCS)
Email: Juliane.Steinhardt(at)nioz.nl
Telephone: +31 (0)222 369 351

About:

 

PH.D. Project: 

GATEWAYS - The Project

Multi-level assessment of ocean-climate dynamics:
A gateway to interdisciplinary training and analysis
FP7 Marie Curie Action: “Networks for Initial Training

Planktonic foraminifera are unicellar protists that precipitate a calcium carbonate shell within the ocean’s water column and are recorders of upper water column hydrographic changes.

During my Ph.D. research, I focused on the biomineralization of planktonic foraminifera and examined in high resolution the species-specific imprint of hydrographical controls on the geochemistry of carbonates formed by planktonic foraminifera.

I began my research by investigating whether planktonic foraminifera collected in a sediment trap, deployed in the narrow of The Mozambique Channel, can record seasonal signals, such as those produced by commonly occurring Eddies. This included the investigation of foraminiferal fluxes and the relative species abundances in respect to environmental conditions and the occurrence of eddies.

The Mozambique Channel is one of the major source areas feeding into the Agulhas Current, thereby presenting a major upstream control on Agulhas leakage. The Mozambique Channel is characterized by passage of large anticyclonic eddies, resulting in temporal deepening of the thermocline. We use material is from sediment traps that intercept the export fluxes settling out from within the Mozambique Channel to determine eddy variability.

Single-chamber trace element composition of these foraminifera revealed a close coupling with hydrographic changes induced by anti-cyclonic eddies. The Mg/Ca values of planktonic foraminifera, analyzed with LA-ICP-MS, revealed that during eddy conditions the thermal gradient between the surface water and the thermocline is reduced whereas the gradient between thermocline and deep water is larger [Steinhardt el al, 2014].

In order to develop more precise paleo-reconstructions based on foraminiferal calcite, it is important to know the range of depth-related environmental conditions that are recorded during the calcification of foraminiferal shells. I hence investigated the vertical migration of planktonic foraminifera through the water column during their life cycle and looked at the range of conditions they would thus encounter as they grow and calcify. This was realized through a combination of measuring single-chamber Mg/Ca with single shell δ18O and δ13C. The species-specific Mg/Ca, δ13C and δ 18O data combined with a depth-resolved mass balance model confirmed distinctive migration and calcification patterns for each species as a function of hydrography [Steinhardt et al., 2015]. Whereas single specimen δ18O did not always reveal changes in depth habitat related to hydrography (e.g. temperature), measured Mg/Ca of the last chambers can only be explained by active migration in response to changes in temperature stratification. Hence, my results indicate that while single chamber Mg/Ca is most affected by eddy frequency, seasonality is reflected more clearly in single test δ18O.

Furthermore, I was interested in the crust formation, observed on several species of foraminifera. Past climate reconstructions using planktonic foraminifera can be biased by low Mg/Ca crust and cortex calcite, which is formed during the terminal stages of planktonic foraminifera. On the other hand, these carbonate phases might have the potential to develop novel proxies. Applying laser ablation ICP-MS profiling I could assess variability in thickness and Mg/Ca composition of the shell wall of three encrusting species (N. dutertrei, P. obliquiloculata and G. scitula). Utilizing these results I presented a model explaining compositional differences within individuals and between successive chambers as well as compositional heterogeneity of the crust and lamellar calcite in all three species studied [Steinhardt et al., 2015].

 

Postdoctoral research: 

ARAMACC Postdoc Project: Exploiting the commercial potential of sclerochronology in environmental monitoring

For my ARAMACC ER position I was working with John Hartley at Hartley Anderson Ltd. in Aberdeen.

I was particularly interested in connecting the research efforts within the ARAMACC project with the commercial and regulatory sectors. The aim was to assess newly developed and optimized practical applications of sclerochronology and maximize their potential incorporation into the regulatory and commercial sectors. As an interface between the commercial and academic sector, I collaborate closely with all the ESRs and Supervisors within the project to:

  • identify new sampling strategies;
  • identify new species for sclerochronological analysis;
  • develop protocols for routine monitoring strategies;
  • apply crossdating and geochemical techniques to existing and upcoming environmental monitoring contracts.

We have summarized the current state of the art sclerochronological research and their potential applications for novel environmental monitoring in a recently published review article [Steinhardt et al., 2016].

At present: DUSTTRAFFIC Project (Postdoc at the Royal NIOZ)

Publications:

2015
  • Pear reviewed article Steinhardt, J.; de Nooijer, L.J.; Brummer, G.-J.A.; Reichart, G.J. (2015). Profiling planktonic foraminiferal crust formation. Geochem. Geophys. Geosyst. 16: 2409-2430. dx.doi.org/10.1002/2015GC005752 link to complete reference
  • Pear reviewed article Steinhardt, J.; Cléroux, C.; de Nooijer, L.J.; Brummer, G.-J.A.; Zahn, R.; Ganssen, G.; Reichart, G.-J. (2015). Reconciling single-chamber Mg / Ca with whole-shell d18O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel. Biogeosciences 12: 2411-2429. dx.doi.org/10.5194/bg-12-2411-2015 link to complete reference
  • Steinhardt, J. (2015). Planktonic foraminifera – Geochemical variability, eddies and seasonality in the Mozambique Channel. PhD Thesis. Vrije Universiteit Amsterdam: Amsterdam. ISBN 9789053831274. 284 pp. hdl.handle.net/1871/53242 link to complete reference
2014
  • Pear reviewed article Steinhardt, J.; Cléroux, C.; Ullgren, J.E.; de Nooijer, L.J.; Durgadoo, J.V.; Brummer, G.J.A.; Reichart, G.J. (2014). Anti-cyclonic eddy imprint on calcite geochemistry of several planktonic foraminiferal species in the Mozambique Channel. Mar. Micropaleontol. 113: 20–33. dx.doi.org/10.1016/j.marmicro.2014.09.001 link to complete reference