Wednesday, 10 June 2015

Meet the TW:eed Team: Emma Reeves, palynologist

This time we have a guest blog by Emma Reeves, palynology Research Assistant at the University of Southampton, who will take us through what she does on a day-to-day basis to discover more about the tetrapod world.
Working for the University of Southampton, I’m responsible for studying spores- microscopic plant fossils of the West Mains Farm Borehole, Norham. These date from the Early Carboniferous geological Period and are over 350 million years old. They’re a lot like pollen but from a time before seeds had become common.

In the autumn of 2013, I spent 4 weeks sampling the borehole core sediments for likely spore-producing layers. The spores were then extracted using various techniques, before being mounted onto slides for study using a microscope.

Measuring core sample depths at the National Geological Repository at BGS, Nottinghamshire
I took 15 g samples from the dark grey, fine grained layers, avoiding the red or bright green sediments as they would have been too oxidised for the spores to have been preserved. I processed 361 samples, which represents approximate intervals of 1 m from the base of the core to the top. This took me over 7 months to complete in the Palynology Laboratory at the University of Southampton.

A sample bag containing sediment to be processed for spores
The first stage of the processing is to crush the rock samples into small pea-sized chunks to increase the surface area for the acids to work on. I also weighed the samples ensuring that I have 5 g each time. The crushed rock is put into a plastic container in a fume cupboard. Wearing special acid-resistant protective clothing, I add 1 cm of hydrochloric acid to each sample and leave them over night. This acid removes any carbonates in the rock.

Palynology samples in containers in a fume cupboard with hydrochloric acid
The next day I pour off the reacted acid, which goes from clear to bright yellow, and fill up the containers with water to dilute any remaining acid. This acidified water is poured off and replaced with fresh until acid test strips tell me that the water is pH neutral. Then I pour off the water and add 1 cm of hydrofluoric acid. This is potentially very hazardous so I wear lots of protective clothing to protect me from any splashes! Again the samples are left over night and the following day I have to shake the containers to make sure that the acid reaches far into the rock. The hydrofluoric acid is used to break down the silicates in the rock. This is why we have to use plastic containers because the acid would quickly dissolve glass beakers as they are also made from silicates.

Carefully pouring off hydrofluoric acidified water during the neutralisation process wearing lots of protective clothing!
The following day I have to pour off the hydrofluoric acid and repeatedly wash the sample in the same way as I did for the hydrochloric until the water becomes pH neutral. Then I use a jet of water to push the residue through a 15 µm (0.015 mm) meshed sieve to catch all of the plant spores; anything smaller goes down the sink! After sieving, each sample is washed into a glass beaker in 25 ml of water. Another 25 ml of hydrochloric acid is added and this is heated to boiling point for 60 seconds before being diluted and sieved again. This removes any insoluble fluorides which result from the hydrofluoric acid reacting with the sediment.

Boiling a sample in hydrochloric acid to remove fluorides
The next stage is to put the sieve residue into vials, but, because I’m also studying megaspores, which tell us about the larger plants e.g. the lycopod trees, I have to wash them though a 150 µm (0.15 mm) mesh first, which separates them from the smaller spores. I then hand pick the megaspores using a fine glass pipette attached to a tube that you hold in your mouth provide suction. I then put the megaspores onto coverslips before making them into microscope slides. The smaller spores are diluted and squirted onto the coverslip, along with anything else that’s mixed in e.g. tiny pieces of charcoal.

Sieved plants spores (and other things) at the bottom of the vials

This is what a finished microscope slide looks like (the black dots are fossils)
The final stage is for me to study the slides and complete a palynology logging sheet for each one. Here I note down the positions of the spores so that I can photograph and identify them. 

A photograph of a spore from the Norham West Mains Farm borehole (50 µm = 0.05 mm)
Once I’ve identified the spores, I’ll produce range charts which show which species are found at which depth in the core. This is the next stage of the process for me and will allow us to build up a picture of the plant life in the area and see how the environment changed through time.

Thank you Emma for explaining your research with us - fascinating!

Until next time