Forams in the laser sights – getting the most out of laser ablation ICPMS analysis of planktic foraminifera

Project Rationale:

Planktic foraminifera are unicellular protists that secrete a 100-1000 m multi-chambered shell during their four week life cycle. Accumulations of their dead shells form a major component of many deep sea sediments and, because the composition of their shells varies as a function of the environment and water chemistry, they are a major palaeoclimatological tool. Foraminiferal shells are however formed under tight biological control, causing a departure from thermodynamic equilibrium for many chemical systems. This results in so called “vital effects” that require some level of empirical calibration [1].

The standard approaches of foraminiferal analysis is to aggregate 10-100 individuals to get sufficient material for analysis that averages across time and/or individual level variability in vital effects. All this averaging obscures individual- and environmental-level variation, which is paramount when partitioning sources of variance in chemical composition. Laser ablation analysis offers the potential to reconstruct past environments at a much finer granularity, especially as it is possible to target not just individual foraminifera, but also individual growth stages [2].

This PhD will exploit several novel analytical tools and approaches to overcome these analytical and biological challenges to realise the full potential of finer resolution laser ablation ICPMS.

Methodology:

Planktonic foraminifera are ideally suited as vital effect case studies because a mature fossil taxonomy underpins their evolutionary relationships. Integrating across data sources will provide unique insights into the causes of individual-level variations in trace element composition that currently cloud the robust reconstruction of past climates.

The first part will investigate the use of Elemental Scientific’s Dual Concentric Injector (http://www.nwrlasers.com/accessories/injector/), which allows very rapid transmission of the ablated material to the mass spectrometer. The transmission speed will increase the rapidity of analyses, lower detection limits, and offer a ready means to reconstruct depth profiles of the ablated shells with unprecedented detail [2]. By comparing to bulk chemical analyses we will have a check of the accuracy of the laser ablation approach and an fuller appreciation of the extra information locked within each individual test.

The second part will leverage x-ray computer tomographic scans collected in the PISTON project (https://www.southampton.ac.uk/oes/research/projects/piston-does-developmental-plasticity-influence-speciation.page) to explore whether laser ablation can yield information beyond the chemical composition of the material ablated. Specifically, the PhD will investigate whether shell thickness and porosity [3] can be quantified simultaneously from the ablation duration and the Ca-ion yield.

Finally, we will use our improved analytical techniques to better understand vital effects through analysis of live foraminifera cultured in Bermuda (leveraging work on the SWEET project; http://www.thefosterlab.org/sweet). These foraminifera will have been studied with micro-electrodes to identify the magnitude of key life processes at the individual level (respiration, calcification, photosynthesis).

Training:

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted in the School of Ocean and Earth Science, which cohabits the National Oceanography Centre Southampton. Specific training will include:

The analysis of foraminifera using laser ablation inductively coupled plasma mass spectrometry.
The establishment of relational databases, data management and statistical analysis of time-series data.

In addition to these project specific skills the student will also be able to attend relevant lectures offered in SOES and across the University. We also anticipate that the project will involve the collection of living foraminifera on a research cruise and the student will have the opportunity to carry out culturing of the foraminifera at the Bermuda Institute of Ocean Sciences (www.bios.edu).