Pigment Potential: How Mud Unlocks the Past
by Jodie Brown
Pigments of the past
Plants and algae get their colour from pigment molecules (i.e., what makes leaves green). Pigments are used to absorb light from the sun and convert this to useful energy for growth. The presence of a variety of pigments in each organism increases the amount of light it can absorb - so it can grow more.
My work involves identifying pigments from dead algae and plants, found in lakebed sediment around the deltas. This information is important as it can tell us about the ecosystem and environment at the time the sediment was deposited.
To look back into the past, we need to look below the Earth’s surface. To do this, we take cores of sediment from the lakebed. As sediment accumulates over time it forms layers, so the sediment at greatest depth is the oldest. Looking at the vertical profile allows us to see changes in the ecosystem over time, and from this (in conjunction with lots of other techniques) we can infer environmental conditions.
Day to day technician life
A typical day in the lab involves preparing and analysing samples from various Asian deltas. I’m working on samples from Vietnam, India and Bangladesh.
I measure the mass of each sediment sample, then add chemicals to extract the pigments and leave overnight in the freezer. When I come back in the morning, I’ve got vials of green (sometimes very bright) solutions, containing pigments recovered from the sediment. This works because the pigment molecules interact with the added chemicals, so they are drawn out of the sediment and into solution.
Visual respresentation of the different stages of sample preparation. (Jodie Brown)
Jodie working in the lab, pouring green liquid (Teresa Needham)
Jodie in the lab topping up HPLC solvents (Jodie Brown)
Next, I filter the pigment solution using little syringes and detachable filters. This removes any bits of sediment, giving a ‘clear’ liquid. I then dry each sample using a flow of nitrogen gas- this helps the chemicals evaporate, leaving a dry residue. The next step is to add a smaller amount of solvent, to transfer the sample to a smaller vial, and then put it in a machine . This separates each sample into individually detectable components, so you can see each pigment present in the sample.
Once the samples have all been analysed, I identify pigments present in each, and calculate their concentrations. To identify the pigments, we use information about how they interact with light because they all have slightly different colours. This is the most time-consuming step, as there are lots of components in each sample, a lot of which aren’t particularly clear to identify!
The pigments break down in the presence of light, so I do all my lab work in relative darkness, with just a lamp in the corner! This makes some of the work more difficult, but it’s crucial for getting the best data. And you get used to it!
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