Past research has uncovered a shift in herbivore collagen δ15N values during the Middle to Late Bronze Age (3700–2750 BP) in Ireland, attributed to intensified land-use - another example in a growing body of evidence that suggests that the Anthropocene concept (whereby humans have made significant impacts to the Earth's systems) began far earlier than previously thought (the ‘Palaeoanthropocene’). While human activity was clearly an important driver of this shift, it remains possible that climate may also have played a role. In Ireland, this shift in δ15N appeared to be sustained despite subsequent reforestation, suggesting that Bronze Age and later peoples left a profound biogeochemical mark on the environment. Here, we revisit this topic, presenting new stable isotope (δ15N and δ13C) measurements from directly radiocarbon-dated wild and domesticated adult herbivorous ungulate bones from the Bronze and Iron Ages, with the aim of constraining the timing of this shift and disentangling the role of human land use from climatic influences. A sustained nitrogen isotopic shift was constrained to ca. 3000 cal BP. Notably, during the Iron Age, a time of widespread reforestation, wild and domesticated herbivorous ungulates exhibited δ15N values that were not significantly different from one another. This suggests that, while the δ15N shift was initiated by land-use change, climate variability, particularly shifts towards warmer and drier conditions during the Late Bronze/Iron Age transition and later Iron Age, may have contributed to its persistence. This study refines the chronology of nitrogen cycle changes in Ireland, demonstrating that human activity initiated a long-term shift in δ15N values during the Late Bronze Age, but that climatic factors may have played a role in maintaining elevated δ15N values during periods of reduced land use. These findings underscore the complexities of understanding the nitrogen cycle in ancient environments and highlight the potential interplay between anthropogenic and environmental drivers of biogeochemical change.

中文翻译：

---

人类活动和气候在爱尔兰工业化前氮转移中的双重作用

过去的研究发现，在爱尔兰青铜时代中后期（3700-2750 BP）期间，食草动物胶原蛋白 δ15N 值发生了变化，这归因于土地利用的集约化——越来越多的证据表明，人类世的概念（人类对地球系统产生了重大影响）比以前认为的要早得多（“古人类世”）。虽然人类活动显然是这种转变的重要驱动力，但气候也可能起到了作用。在爱尔兰，尽管随后重新造林，但 δ15N 的这种变化似乎持续存在，这表明青铜时代和后来的人类在环境中留下了深刻的生物地球化学印记。在这里，我们重新审视了这个主题，提出了来自青铜和铁器时代直接放射性碳测年的野生和驯化成年食草有蹄类动物骨骼的新稳定同位素（δ15N 和 δ13C）测量值，目的是限制这种转变的时间，并摆脱人类土地利用与气候影响的作用。持续的氮同位素变化被限制在大约 3000 cal BP。值得注意的是，在铁器时代，一个广泛重新造林的时期，野生和驯化的食草性有蹄类动物表现出的 δ15N 值彼此之间没有显着差异。这表明，虽然 δ15N 变化是由土地利用变化引发的，但气候变率，特别是在青铜器时代晚期/铁器时代过渡期和铁器时代后期向更温暖和干燥条件的转变，可能是导致其持续存在的原因。 本研究完善了爱尔兰氮循环变化的时间顺序，表明人类活动在青铜时代晚期引发了 δ15N 值的长期变化，但气候因素可能在土地使用减少期间维持较高的 δ15N 值方面发挥了作用。这些发现强调了理解古代环境中氮循环的复杂性，并强调了生物地球化学变化的人为和环境驱动因素之间的潜在相互作用。