The stable isotopes of nitrogen in nitrate archived in polar ice have been interpreted as reflecting a shift in reactive nitrogen sources or changes in atmospheric chemical reactivity. Here, we present a novel concentration and isotopic record of nitrate (δ¹⁵N-NO₃⁻) from a central Tibetan Plateau ice core over the last ~200 years. We find that nitrate concentration increased from 6.0 ± 2.3 μeq/L (mean ± 1σ) in the preindustrial period (prior to 1900s) to 7.3 ± 2.7 μeq/L in post-1950. Over the same time period, the δ¹⁵N-NO₃⁻ decreased from 8.7 ± 3.7‰ to 4.2 ± 3.1‰, with much larger interannual variation in δ¹⁵N-NO₃⁻ during the preindustrial period. We present a useful framework for quantifying the sensitivity of the isotopic composition of atmospheric nitrate to changes in both sources and chemistry (gas and aerosol phase). After 1950, nitrogen deposition is primarily driven by fertilizer use, leading to significant increases in concentration and decreases in δ¹⁵N-NO₃⁻. The large interannual variability of ice core δ¹⁵N-NO₃⁻ in the preindustrial reflects natural processes, namely the El Niño Southern Oscillation (ENSO) and dust events. Our results highlight a new connection between the nitrogen cycle and ENSO, and the overprinting of natural climate signals by recent anthropogenic increases in reactive nitrogen release.

极地冰中储存的硝酸盐中氮的稳定同位素已被解释为反映了反应性氮源的变化或大气化学反应性的变化。在这里，我们提出了一个新颖的浓度和硝酸的同位素记录（δ ¹⁵ N-NO ₃ ^- ）从中央高原冰芯过去〜200年。我们发现硝酸盐浓度从工业化前时期（1900年前）的6.0±2.3μeq/ L（平均±1σ）增加到1950年后的7.3±2.7μeq/ L。在相同的时间期间内，δ ¹⁵ N-NO ₃ ^-从8.7±3.7‰，δ下降到4.2±3.1‰，大得多际变化¹⁵ N-NO ₃ ^-在工业化之前。我们提出了一个有用的框架，用于量化大气中硝酸盐的同位素组成对来源和化学变化（气相和气溶胶相）的敏感性。1950年后，氮沉积主要由肥料利用驱动，从而导致浓度显著增加和减小δ ¹⁵ N-NO ₃ ^- 。冰核的大际变化δ ¹⁵ N-NO ₃ ^-工业化之前的现象反映了自然过程，即厄尔尼诺南方涛动（ENSO）和尘埃事件。我们的结果强调了氮循环与ENSO之间的新联系，以及最近人为增加的活性氮释放量对自然气候信号的叠印。