Pollen analysis

Pollen analysis is underway on the sequence from Red Loch and further updates will follow on the pattern of vegetation change being seen in the levels being investigated. Those levels currently being analysed show good preservation of pollen and non-pollen palynomorphs (NPPs), such as fungal spores. Photographs taken from the pollen slides showing some of the types of fossil pollen and spores present are provided here.

Radiocarbon dating

The radiocarbon dates have been returned from the peat samples sent off for dating at the Scottish Universities Environmental Research Centre (SUERC) labs. Two dates, one from the base of the core taken at 7.48m and one taken at 2.48m have added important information to the chronology of the peat deposit sequence. These dates compliment the two previous dates we have from the site, which were taken during the assessment stage.

All four of the dates we currently have are shown in the table. The dates returned from the peat samples show that peat accumulation began at the site during the Early Holocene at approximately 8709-8488 cal BC (SUERC-37141) and continued to accumulate, through into the Post Medieval period at cal AD 1420-1620 (SUERC-32308) and given the depth this sample was taken from is probably still continuing to accumulate today. 

Radiocarbon dating results from Red Loch, Isle of Bute

The radiocarbon dates from Red Loch can be plotted against peat depth to make an age/depth graph for the sequence (see graph). This graph assumes the accumulation of peat at Red Loch has been uniform over time between the radiocarbon dated levels in order to allow for a rough calculation of which periods the non-dated areas of the core represent. There is clearly a margin of error made based on this assumption, which is illustrated by the two bottom dates as they lie some distance from the overall trend line (linear) for peat accumulation. Further radiocarbon dating of the core in the future would aid in refining this chronology even further and help to narrow the margin of error in locating archaeological periods within the core. For now though this is evidently a useful chronological guide in showing which periods are represented by the Red Loch sequence.

Sub-sampling

Once back in the lab the cores are recorded in order determine any changes in stratigraphy, such as changed from a wood peat, signalled by the presence of frequent wood fragments within the peat to a sedge peat, signalled by the presence of monocotyledon plant fragments (such as grasses and sedges) within the peat.

The cores are then sub-sampled for pollen analysis. Pollen samples are taken in small cube blocks (c.1cm3), cut into the peat and placed into small plastic bags (see photo). These will then be sent to The University of Aberdeen for preparation, once prepared the samples will be sent back to us ready for pollen counting. Any wood fragments that can be identified were also removed from the cores. Identification of the wood to taxa will provide further information on the local vegetation communities growing on the bog surface and help to indicate what tree pollen represents local woodland as opposed to more regional woodland.

Pollen samples

Lastly the cores have been sub-sampled for radiocarbon dating material. The peat itself has been used for dating from the Red Loch sequence and it is hoped these dates will ties in with the previous work done at the Loch and help to overlap the two sequences.

Laboratory work

The majority of the work carried out will be done in the lab with sub-sampling and pollen counting all taking place here. Regular updates to this work will be posted on this blog.