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

Abstract

The Anthropocene is often linked to the Industrial Revolution due to the rapid increase in fossil fuel consumption and societal shifts. However, emerging discussions around the 'Palaeoanthropocene' suggest that significant human impacts on Earth’s systems may have started much earlier. This PhD thesis investigates nitrogen cycle changes during the Irish Bronze Age, a period marked by substantial human activity and climate change. By analysing herbivore bone collagen and the geochemistry (δ15N, δ13C, C:N) of lake sediments and peat cores, the research explores the extent and origins of nitrogen isotopic shifts . Pollen and testate amoebae analyses were used to reconstruct land-use and palaeohydrological conditions, enabling a multi-proxy approach to assess both climate- and human-driven changes. The study reveals asynchronous nitrogen cycle shifts between herbivore remains and lake systems, reflecting local land-use variations. Around 3000 cal BP, a permanent shift in herbivore δ15N values was identified, persisting through the Iron Age, but this shift is not immediately reflected in sediment sequences. Two lake sites show permanent nitrogen enrichment beginning around 2600 cal BP, peaking around 1500 cal BP, associated with renewed anthropogenic activity. The research also examines the role of climate, suggesting that droughts may have sustained elevated δ15N values during periods of reduced human impact. This highlights a complex interaction between climate and human land-use. The findings challenge traditional assumptions about the timing of human impacts on the nitrogen cycle, suggesting earlier and more gradual changes. The thesis advocates for re-evaluating the onset of the Anthropocene, proposing that significant anthropogenic environmental changes may date back to prehistory.

Thesis embargoed until 31 December 2029.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	NERC QUADRAT
Supervisor	Gill Plunkett (Supervisor), Neil Ogle (Supervisor) & Kate Britton (Supervisor)