Pollen Analysis

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The lower monolith from Trench 9.  The small polystyrene markers show the locations of pollen sub-samples
The lower monolith from Trench 9. The small polystyrene markers show the locations of pollen sub-samples

Thank you Emily for the update πŸ™‚

As part of the post-excavation analysis, we have processed sub-samples of sediment from the Trench 9 monoliths for pollen analysis. Pollen is very tough and can survive for thousands of years. Preservation is best where sediments are waterlogged and acidic – waterlogging creates anaerobic conditions and stops microbial activity that can break down the pollen grains. Highly organic sediments (usually dark in colour and containing plant macrofossils such as leaves and stems) are likely to be full of pollen, but it can sometimes be found in less organic soils and sediments if the conditions are right. So, are they right at Brockhampton? The sediment is red and does not look particularly organic, but it was wet, so it is worth checking whether pollen has survived.

Pollen samples being heated in a waterbath during hydrofluoric acid treatment. The heat helps the acid to break down silica (e.g. sand) in the samples. Our centrifuge can be seen to the left - this is used to spin the samples at 3000 revolutions per minute to force the pollen to the bottom of the test-tube, allowing the remaining acids/alkalis to be poured away without losing the pollen.
Pollen samples being heated in a waterbath during hydrofluoric acid treatment. The heat helps the acid to break down silica (e.g. sand) in the samples. Our centrifuge can be seen to the left – this is used to spin the samples at 3000 revolutions per minute to force the pollen to the bottom of the test-tube, allowing the remaining acids/alkalis to be poured away without losing the pollen.

First, 0.5cm3 samples were taken at regular intervals throughout the profile. We used an alkali to destroy organics (other than pollen!) and concentrated acids to remove silica and cellulose within the samples – the aim is to get rid of everything except for the pollen, as this makes it easier to see and identify. The extraction process has many stages and it takes a full day in the laboratory to process one set of pollen samples. The samples are usually left to dry overnight, before they can be mounted to microscope slides for analysis.

If pollen or other microfossils are present in the sediments, it may be possible to find out what the landscape was like at Brockhampton in the past, and how it changed over time. For example, was there woodland around the site, and if so, what kind of trees were growing? Did people plant crops or keep livestock in the area? Did the inhabitants have a kitchen garden? Before we can try to answer any of these questions, we need to know whether pollen is preserved in the sediments – the samples should be dry soon…

Dr Emily Forster
PDRA in Archaeobotany and Associate University Teacher in Archaeopalynology and Environmental Archaeology
University of Sheffield Department of Archaeology

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