Reconstructing the health and productivity of coral reef systems at high resolution: Laser ablation analysis of boron and carbon isotopes in corals
Coral reefs face numerous threats worldwide, not least amongst these is ocean acidification (OA) – the decline in the pH of ocean waters in response to increasing anthropogenic CO2 emissions. pH in coral reefs is however very dynamic, varying dramatically on multiple scales of space and time (microns to km’s and minutes to years) and is a function of both the pH of open ocean water and a number of biophysical processes that occur on the reef (net ecosystem calcification, NEC, and net ecosystem productivity, NEP). These high frequency and local changes in pH need to be understood and documented before the full impact of ocean acidification can be determined (e.g. Hoffmann et al. 2011).
Stony corals precipitate a skeleton of aragonite at rates of up to 2 cm/yr in well-defined annual bands, like tree rings. The boron and carbon isotopic composition of this aragonite can provide unique insights into the pH and productivity experienced by the coral during its life time (e.g. Fowell et al. 2018). The temporal resolution of these reconstructions using state of the art, but laborious, bulk sampling techniques is however currently monthly at best. It is the aim of this project to fully exploit the record of past environment encapsulated in coral skeletons by developing new micro-sampling techniques for boron and carbon isotopes using laser ablation multi-collector inductively coupled plasma mass spectrometry.
Laser ablation (LA) techniques represent a unique opportunity for the Earth Sciences, especially when applied to incrementally grown biominerals like coral skeletons. Here we will build on several recent studies (e.g. Chen et al. 2017 & Fietzke et al., 2016) to develop novel techniques using inductively coupled plasma mass spectrometry (ICPMS) to enable the accurate and precise determination of the boron and carbon isotopic composition, simultaneously with the trace element composition of coral skeleton, at a weekly and potentially shorter resolution. In particular, we will focus on the information revealed by elemental and isotopic mapping of the coral skeleton (e.g. Fietzke et al. 2016). This work will be carried out in collaboration with engineers at ThermoScientific and Elemental Scientific to fully exploit the latest in laser and mass spectrometric technology to enhance machine sensitivity and improve 2D isotopic imaging capabilities.
Applications of the new techniques developed will be focused on using boron and carbon isotopes to track the interplay between biophysical processes on the reef and anthropogenic carbon uptake in the Bermuda and Belize coral reef systems (e.g. Fowell et al. 2018). The high-resolution, multiproxy approach will also provide unique insights into biomineralization in tropical corals (and other calcifying organisms) and will have many immediate applications outside of immediate aims of this project.
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. Specific training will
(a) Training In the operation of laser ablation and its simultaneous coupling to multiple mass spectrometers using split-streaming.
(b) Training in the measurement of boron and carbon isotopes by LA-MC-ICPMS and trace elements by LA-ICPMS.
(c) Training in coral sample preparation and milling for solution based analysis.
Training in trace element and isotopic imaging by laser ablation mass spectrometry and scanning electron microscopy.
This is a CASE funded project and we anticipate regular communication with our CASE partners (http://www.icpms.com/ and https://www.thermofisher.com/uk/en/home.html) and the successful student will be able to spend a total of 3 months as a placement at the relevant factories. Beyond the opportunities for travel offered by INSPIRE there will also be opportunities to partake in field work associated with ongoing coral reef research and palaeoclimate at the Foster lab (www.thefosterlab.org).
To find information on ‘how to apply’ for a GSNOCS PhD project please click the following link:http://noc.ac.uk/education/gsnocs/how-apply
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Chen, W. et al. (2017) In Situ Carbon Isotope Analysis by Laser Ablation MC-ICP-MS, Analytical Chemistry, 89 (24), pp 13415–13421, doi:10.1021/acs.analchem.7b03678
Fowell, S, Foster, G.L., Ries, J., Castillo, K.D., de la Vega, E., Tyrrell, T., Donald, H.K., Chalk, T.B. (2018) Historical trends in pH and carbonate biogeochemistry on the Belize Mesoamerican Barrier Reef System, Geophysical Research Letters, 45, doi: 10.1002/2017GL076496.
Fietzke, J. et al. (2015) Century-scale trends and seasonality in pH and temperature for shallow zones of the Bering Sea, Proceedings of the National Academy of Science, 112, 2960-2965, https://doi.org/10.1073/pnas.1419216112
Hofmann GE, Smith JE, Johnson KS, Send U, Levin LA, Micheli F, et al. (2011) High-Frequency Dynamics of Ocean pH: A Multi-Ecosystem Comparison. PLoS ONE 6(12): e28983. https://doi.org/10.1371/journal.pone.0028983