Vacancy for a PhD candidate at Ghent University
Optical characterization and robotic monitoring of biogenic carbon particles in the epi- and mesopelagic ocean
Promotor: Griet Neukermans, Marine Optics and Remote Sensing Group, Faculty of Sciences
Co-promotor: Kristiaan Neyts, Liquid Crystals and Photonics Group, Faculty of Engineering
The downward flux of biogenic particles exerts an important control on atmospheric CO2 levels and global climate. Biogenic carbon particles are generated in the sunlit ocean surface and comprise Particulate Organic and Inorganic Carbon (POC and PIC). The differentiation is crucial because the downward flux of POC helps to remove CO2 from the atmosphere while the downward flux of PIC has the opposite effect. Autonomous ocean robots with bio-optical sensors now study biogenic carbon particles in the upper ocean (0-1000 m depth) and provide observations at unprecedented rates. However, an optical sensor to estimate PIC independently is currently lacking, and hence the effect of POC and PIC cannot be differentiated.
Promotor: Griet Neukermans, Marine Optics and Remote Sensing Group, Faculty of Sciences
Co-promotor: Kristiaan Neyts, Liquid Crystals and Photonics Group, Faculty of Engineering
The downward flux of biogenic particles exerts an important control on atmospheric CO2 levels and global climate. Biogenic carbon particles are generated in the sunlit ocean surface and comprise Particulate Organic and Inorganic Carbon (POC and PIC). The differentiation is crucial because the downward flux of POC helps to remove CO2 from the atmosphere while the downward flux of PIC has the opposite effect. Autonomous ocean robots with bio-optical sensors now study biogenic carbon particles in the upper ocean (0-1000 m depth) and provide observations at unprecedented rates. However, an optical sensor to estimate PIC independently is currently lacking, and hence the effect of POC and PIC cannot be differentiated.
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The first objective of this PhD thesis is the calibration of a novel cross-polarized beam transmissometer developed by the MarSens group for the detection of delicate calcium carbonate PIC structures. This material is anisotropic and the strong optical birefringence changes the polarization of transmitted light. In the lab of the LCP group these particles can be observed and characterized with a polarization microscope. The aim is to achieve an accurate quantification of PIC (and CaCO3) concentration in seawater samples from the new sensor. The second objective is the quantification of the downward fluxes of PIC and POC using observations from an array of robotic ocean profilers in the Atlantic Ocean, equipped with bio-optical sensors, including the new PIC sensor. This will allow to quantify the net capacity of the ocean to remove atmospheric CO2. The third objective is to examine the PIC ballast hypothesis, which posits that the downward transfer of POC when associated with high-density PIC is faster and more efficient. Using simultaneous depth-resolved PIC and POC observations at large spatiotemporal scales provided by the robotic profilers, it should finally become possible to address this hypothesis that has been heavily debated due to lack of appropriate observations.
The PhD thesis research comprises: 1) validation and calibration of the PIC sensor in the lab and in the field; 2) estimation of the mean particle size based on statistical analyses of high-resolution signal time series; 3) deployment of robotic floats to characterize particles and measure optical properties in natural waters; 4) development of algorithms to characterize the composition and size of biogenic carbon particle populations using a suite of optical measurements (bulk particle backscattering, unpolarized transmission, cross-polarized transmission, chlorophyll fluorescence,…); 5) application of the developed algorithms to quantify PIC and POC to robotic optical observations; 6) examination of the PIC ballast hypothesis.
We are looking for a candidate with at the same time a good understanding of optical measurement systems and a strong interest in marine sciences. The candidate should be willing to conduct experiments in the lab and do work in the field, should have a talent for statistical signal analysis, and a good working knowledge of spoken and written English. This topic is a clear example of multidisciplinary work (involving two faculties) in a flexible and dynamic environment, under the supervision of two research oriented promotors. The candidate should have an open mind and good programming skills (mathematica and/or matlab).
Starting date: preferably October 1, 2020 - but flexible
Interested? Send your CV and short motivation letter to griet.neukermans@ugent.be and kristiaan.neyts@ugent.be.
The PhD thesis research comprises: 1) validation and calibration of the PIC sensor in the lab and in the field; 2) estimation of the mean particle size based on statistical analyses of high-resolution signal time series; 3) deployment of robotic floats to characterize particles and measure optical properties in natural waters; 4) development of algorithms to characterize the composition and size of biogenic carbon particle populations using a suite of optical measurements (bulk particle backscattering, unpolarized transmission, cross-polarized transmission, chlorophyll fluorescence,…); 5) application of the developed algorithms to quantify PIC and POC to robotic optical observations; 6) examination of the PIC ballast hypothesis.
We are looking for a candidate with at the same time a good understanding of optical measurement systems and a strong interest in marine sciences. The candidate should be willing to conduct experiments in the lab and do work in the field, should have a talent for statistical signal analysis, and a good working knowledge of spoken and written English. This topic is a clear example of multidisciplinary work (involving two faculties) in a flexible and dynamic environment, under the supervision of two research oriented promotors. The candidate should have an open mind and good programming skills (mathematica and/or matlab).
Starting date: preferably October 1, 2020 - but flexible
Interested? Send your CV and short motivation letter to griet.neukermans@ugent.be and kristiaan.neyts@ugent.be.
