Investigating the timing and causes of nitrogen cycle changes in Bronze Age Ireland

"A fundamental alteration in the nitrogen cycle during the Bronze Age in Ireland has been identified through isotope analysis of wild and domesticated faunal remains and attributed to intensified land management during this time (Guiry et al. 2018). The timing of the shift broadly coincides with palynological evidence for widespread land clearance in the Middle Bronze Age (~1600 BCE) and Late Bronze Age (~1000 BCE) that supports an anthropogenic explanation for the environmental shift (Plunkett 2009) but a climate driver cannot be ruled out. This project will investigate the timing, extent and potential causes of the nitrogen fractionation shift through a palaeoenvironmental analysis of sedimentary sequences and an examination of dietary evidence spanning the Bronze Age.

Specific research questions include:
1) Is a nitrogen shift detectable in sedimentary sequences, including peatlands which were unlikely to have been directly impacted by intensified farming?
2) Does the archaeological record accurately reflect the extent of Bronze Age land-use, and can intensification be detected during the period of interest?
3) How do changes in land-use manifest in the subsistence record, determined from multi-proxy palaeodietary information from the archaeological record?
4) What was the relationship of land-use and/or nitrogen shifts, if any, to climate change during this period?

Methods
1) Palaeoenvironmental sequences will be collected from suitable lake and peatland sites in areas demonstrating contrasting densities of Bronze Age activity in Ireland (determined from Sites and Monuments Records in the two jurisdictions of the island). Tephrochronology and 14C dating will be used to isolate the Bronze Age levels of the sequences, which will then be investigated at centennial-scale resolution for land-use history (pollen analysis), palaeoclimate (pollen influx; testate amoebae - peatlands only) and delta-N-15 analysis. Higher resolution analysis will be conducted across periods of major transitions to enable the timing of those events to be refined.
2) The relationship between land-use changes, subsistence and diet will be investigated using stable isotope analysis of archaeobotanical, archaeofaunal and human remains from a selection of Bronze Age archaeological sites in Ireland. Previously published data will be integrated into the study alongside newly generated data.

This multi-proxy approach will comprise the first integrated investigation of land-use changes, diet and environmental impacts in Irish prehistory and will enable a deeper understanding of the role of humans in driving systemic ecosystem change."