This collaboration with the University of Southampton used Raman spectroscopy to investigate cores from an ancient climate event. The study was published in Geochemical Perspectives Letters.
The PETM event caused major, rapid global warming of 4-6 °C, which also released large amounts of carbon into the atmosphere. The climate change associated with the event altered hydrological cycles and may have driven erosion and degradation of petrogenic organic carbon (OCpetro), which may have been a further positive feedback in the PETM climate system.
This is the first study to use Raman spectroscopy to investigate OCpetro oxidation at the PETM. We found that there was an increased contribution of graphite during the PETM, likely caused by intensified physical erosion and enhanced OCpetro oxidation.
In areas where there is a range of OCpetro inputs, both graphitic and disordered, Raman spectroscopy appears to be a very promising tool for investigating past changes in the carbon cycle.
This collaboration with the BlueC project at University College Dublin measured organic carbon and BHP biomarkers in saltmarshes from the East and West coasts of Ireland. The paper is published in Sustainable Microbiology.
Organic carbon concentrations were high and very variable, from 0.26% up to 26%, a 100 times increase. Concentrations were particularly high at the top of cores from the upper marsh (furthest from the sea). Comparing this to the BHP data showed that these samples were rich in marine organic matter. Terrestrial BHPs were only found in high concentrations at depth in the oldest cores. Therefore, most of the carbon in the saltmarsh sediments has been brought in on the tide, and the influence of tidal sediment supply on saltmarshes is important for their growth and survival.
This is our first study using BHPs to investigate saltmarshes. The oldest, high-marsh sediments had terrestrial BHP signatures, but everywhere else the source appears to be marine.
My first PhD student, Saule Akhmetkaliyeva, has published her thesis in Science of the Total Environment. Her study compares organic carbon and bacterial communities across three deglaciating Arctic catchments.
Graphical abstract from Akhmetkaliyeva et al., 2025
After a glacier thaws and retreats, the exposed land is usually quite bare and carbon poor. Saule visited deglaciating sites in Sweden, Iceland and Greenland to measure the amount of carbon present in the sediments and the development of soil bacterial communities over time. She found that bacterial communities change as the soil develops and the organic carbon content rises.
Soil sampling in Tarfala Valley, Sweden
In Sweden, the deglaciation was very recent and the soil very thin, with lowest carbon contents and very few soil biomarkers. Iceland had some very young soils, but also some older moraines with age estimates – older moraines had higher carbon contents and a more developed soil bacterial community. In Greenland, the catchment had been deglaciated for thousands of years and a fully-developed ecosystem was present, with the highest amount of organic carbon, plenty of soil-specific biomarkers, and a stable microbial community.
Older, developed soils in Iceland had higher concentrations of organic carbon and a greater proportion of soil-specific BHP biomarkers
In the last few years, I have expanded my research into the burial of carbon in saltmarsh environments, especially around the UK. This is the first paper I have published on the topic. The paper is available Open Access via the journal website.
A composite map/aerial image of the Steart Marshes saltmarsh site
Saltmarshes, which is an coastal wetland which is flooded and drained by saltwater brought in on the high tide, are natural features acrosst the UK and around the world. In the UK, many saltmarshes were drained to form farmland, with a sea defence built between the drained marsh and the river or estuary. Rising sea levels threaten the reclaimed marshes, and the nearby fields, towns and villages, with flooding. Often it is decided that retreating from the drained land is the best way to protect other, more valuable, assets nearby. Through a process called “managed realignment”, the sea defences are breached and the tide returns to the saltmarsh.
Realigned saltmarshes are often lower than the local high tide level, and are rapidly filled with sediment and saltmarsh plants when the water returns. This creates a habitat that can attract wetland birds and, since the sediment has organic carbon associated with it, also generates and opportunity to bury carbon in the marsh.
This paper investigates two things: how much organic carbon was buried on a realigned saltmarsh in the first years after it was created, and how does this carbon burial compare to the emissions generated by the construction of the site.
Samples were collected from Steart Marshes, a site in Somerset, UK, that was flooded in 2014. The samples were analysed for their total carbon and organic carbon content using analytical facilities here at Manchester Met. The carbon concentrations were scaled up to the entire site using sedimentation data calculated from laser scans of the marsh collected at different time points.
There has been a very rapid build-up of sediment at Steart Marshes since the sea defences were breached
We found that the organic carbon burial rate (19 tonnes per hectare per year) was very high compared to other saltmarsh sites, mostly because the sediment built up very rapidly (75 mm per year) after the sea defences were breached. The organic carbon buried on site is much greater than the carbon emissions generated by the diggers and bulldozers used to make the new marsh, and so it seems that there has been a net climate benefit by creating the marsh.
However, the next piece of the puzzle is to fully understand the types of organic carbon being buried on the site. Not all carbon has the same climate benefit associated with it, and so further work is required to properly calculate the climate change mitigation potential of restoring saltmarshes.
Water filters, extracts and column chromatography for the samples from Mahoney Lake
This publication, led by Molly O’Beirne from the University of Pittsburgh is a really exciting look at BHP biomarkers and microbes in an unusual Canadian lake. My role was to measure and identify the BHPs present in the lake, including finding a ‘new’ BHP that had not been described before.
Mahoney Lake, British Columbia, is a small lake with a really high concentration of sulfur, and a low concentration of oxygen. This classifies it as ‘euxinic‘, and Mahoney Lake is 100 times more sulfidic than the Black Sea. Not only that, but the lake switches from oxic to euxinic within the top 7-8 metres, meaning that sunlight can penetrate into the euxinic layer. This study looked at the changing bacterial communities and BHP biomarkers present in the different layers of the lake.
Water filter samples were collected at a series of depths in the lake, from the oxic layer, through the changeover to euxinia (the ‘chemocline’), down to the sediment at the bottom. At the chemocline, a large community of purple sulfur bacteria were collected which made the filters turn a bright pink-purple colour (see the picture above), which makes a nice change from the usual brown-grey water filters usually collected from lakes and rivers.
Chromatogram and mass spectrum showing the novel BHP with m/z 710
Back in the lab in Pittsburgh, these filters were extracted using solvents and the BHP molecules were separated out from everything else, transferred into small vials, and posted across the Atlantic. After a few days in customs, they made it to Manchester Metropoltian to be analysed on the LC-MS. When looking through the data, there were several common BHPs present, but also a large amount of a previously unknown BHP molecule. It was seen on the chromatogram at a similar time to the ubiquitous ‘aminotriol’ BHP, but careful analysis of the mass spectrum showed that the molecule and its fragments were four mass units ligher than aminotriol, with m/z (mass to charge ratio) 710 rather than 714. We think that this molecule has the same structure as aminotriol, but has two carbon-carbon double bonds in the structure.
Since this molecule was only found in the lower parts of the lake, we think it could be directly linked to euxinic environments. In future work, I will look for this molecule in other euxinic and oxic lake samples to test whether it is a reliable biomarker for euxnia. If it is, BHP 710 can be used to identify euxinia in ancient lakes throughout the geological record.
To find out which bacteria might be making these molecules, Trinity Hamilton from the University of Minnesota sequenced the bacterial genomes present in the lake filters. Genes that produce BHPs were found in samples from the lower parts of the lake, and the BHP producing bacteria are probably Deltaproteobacteria, Chloroflexi, Planctomycetia, and Verrucomicrobia.
At the bottom of the lake, the BHPs present change again. Bacteriohopanetetrol (BHT) is the most common, and methylated BHTs are only found in the lake sediments. This makes us think that bacteria living in the oxygen-free sediments at the bottom of the lake are the source of the methylated BHTs, rather than bacteria living in the oxygenated upper layer of the lake.
Overall, this has been a really fun and interesting study to be part of, and provides loads of new research questions as well as answers. Other researchers looking to analyse BHPs in their samples are welcome to get in touch to discuss collaborations.
Typical results when measuring PVC using Raman spectroscopy
A slight detour from my usual environmental chemistry work, this paper was led by PhD student Kate Irvin and looks at characterising PVC samples in an industrial setting, finding ways to optimise the product development process.
When developing a new polymer product, it is important to regularly test its properties and confirm its ingredients. Typical tests take hundreds of hours and can delay the development cycle, adding costs to the process. In this paper we demonstrate some rapid, non-destructive techniques for quantifying the amount of plasticiser (dioctyl terephthalate) and filler (calcium carbonate) within a PVC sample.
Fourier transform-infrared spectroscopy and Raman spectroscopy were used, since they are quick, easy-to-use and non-destructive methods of identifying samples. The time savings alone of using these methods compared to using traditional hardness, softness and tensile tests could reduce product development costs by 50%.
When I joined Manchester Metropolitan University in 2016, I was awarded a small grant to set up an analysis facility measuring a group of molecular biomarkers, bacteriohopanepolyols (BHPs), that are found in environments throughout the world. This paper is the first to be published on BHPs measured at Manchester Met.
Cores of polish lignite used in this study
In this paper, led by Anna Pytlak, samples from two Polish lignite deposits were analysed via LC-MS to see which BHPs were present in the samples, and whether these could be linked to methane-generating bacterial living in the rocks now, or millions of years ago.
My role, along with PhD student Saule Akhmetkaliyeva, was to extract the BHP biomarkers from the sediment samples and analyse them on the time-of-flight mass spectrometer at Manchester Met. The molecules found in the mass spectrometer were compared against known BHP results, and identified as being from various types of bacteria. This included both Type I and Type II methanotrophs (bacteria that consume methane), including some living methanotrophs.
BHP concentrations were higher in the lignite than the surrounding mineral soil, suggesting some form of active bacterial commuity supported by the lignite deposits that cannot be sustained in regular soil. Living methanotrophs means that there’s a chance some of the methane released over time by the lignite is eaten by the bacteria and not released to the atmosphere.
If you would like to measure BHPs in your own samples, please get in touch to discuss collaborations!
A common topic of student research projects is monitoring and assessing the health of rivers around Greater Manchester. This paper represents a particularly good project by Haseeb Mahmood, who was motivated enough to carry his project through to publication.
In this work, Haseeb collected water samples along the length of the River Irwell, which flows from the Pennine Moors to the Manchester Ship Canal. Along its length it passes through industrial, rural, suburban, parkland and urban environments. These all affect the river water quality. For example, there are measurable changes in biological oxygen demand and phosphate concentration as the river passes by sewage treatment works.
Reassuringly, Haseeb measured lower heavy metal concentrations in the river during summer and winter 2019-20 compared to historical measurements on the same river, indicating that clean-up activities in the last 30 years have been worthwhile.
Backscatter electron microscope images of a meteorite
This paper is available as an Open Access article via the journal.
This research paper continues the work of Paula Lindgren, who I worked with earlier when looking at a suite of meteorites. In this paper, a single carbonaceous chondrite meteorite was heated in the laboratory to simulate the heating that took place during the life of a meteorite. A sample was studied using a series of different techniques, including scanning electron microscopy, Raman spectroscopy, infra-red spectroscopy, oxygen isotopic analysis and X-ray diffraction. It was then heated to 400 °C and 800 °C and studied again. We found that the minerals, isotopes and organic matter all changed with heating. Sometimes 400 °C was enough to make a change, sometimes no change was observed until 800 °C.
Changing Raman spectropscopy measurements from unheated (blue), 400 °C (yellow) and 800 °C (red) samples of the same meteorite
These changes can be used to work out the thermal history of meteorites collected on Earth, and even for asteroids sampled in space!
In this paper, published in The Cryosphere, we used Raman spectroscopy to trace carbonaceous material from the shoreline to the furthest reaches of the East Siberian Arctic Shelf.
Raman spectroscopy uses laser light to determine the molecular structure of a wide range of materials. During my PhD, I showed that Raman could be used to probe individual particles of organic carbon to show whether they were disordered, like coal, or crystalline sheets of graphite. This collection of carbon particles, known as carbonaceous materials, are particularly hardwearing and resistant to breaking down during erosion and transport. During my post-doctoral research, I then used a range of organic geochemistry techniques to investigate the transition from terrestrial to marine carbon across the East Siberian Arctic Shelf, showing that coastal erosion and river erosion were both supplying organic matter to the ocean.
Map of the samples used in this study. Red lines are areas of intense coastal erosion
This study uses the Raman technique on those same Arctic Shelf sediments to look at the sources and distribution of carbonaceous material on the shelf. The samples used in our paper were collected from close to the mouths of some major rivers, from areas experiencing rapid coastal erosion, and from hundreds of kilometres offshore.
Groups of spectra found in the shelf samples
The hardest work, collecting over 1400 Raman spectra, was carried out by two undergraduate students, Melissa Maher and Jerome Blewett, who are co-authors on the paper. The collected spectra were then analysed using an automated peak fitting script, and grouped according to the shape of the fitted peaks. This provides an unbiased method for determining whether a carbon particle is highly graphitised, mildly graphitised, disordered, or somewhere in between. For each of the sites on the shelf we collected spectra from up to 30 particles, and looked at how many fitted into each group. Statistics were then used to spot patterns across the shelf.
Distribution of “Disordered” and “Intermediate” carbon
Our first finding is that the relative proportion of “disordered” and “intermediate” carbon particles varies, and that there are patches with more of one or the other group. At the coastline these patches align with two of the major rivers (Kolyma and Indigirka) and areas of rapid coastal erosion. Surprisingly, the patches can then be traced all the way across the shelf. We would have expected the currents in the ocean to have mixed the particles together further offshore, and in the biomarker studies we’ve done before we did not spot this kind of pattern. This means that Raman is a great way to trace the different sediment and carbon sources on the shelf.
“Highly Graphitised” carbon is found in high proportions far offshore
Our second finding is that the amount of “highly graphitised” carbon particles is highest in the furthest offshore samples. These very crystalline flakes of graphite are behaving differently to all the other carbon particle groups. It’s not clear exactly why this is, but one option is that everything else is breaking down and degrading before getting that far offshore. Or, the graphite particles could be so light that they sink very slowly, floating out to the shelf edge much easier than the other types.
This problem has implications for the global carbon cycle. These carbon particles have been released from permafrost on land and transported for hundreds of kilometres offshore, a trip that has taken thousands of years. If all of the carbonaceous material can survive the journey, it means that this fraction of the organic matter is not at risk of being degraded and released to the atmosphere as greenhouse gases. Burying it in the ocean provides protection from degradation for thousands or millions of years. Future studies should look at just how well the carbon particles can survive erosion and burial.
In summary, carbonaceous material is resilient to degradation and can be used to trace sediment sources across the Arctic shelf.
