Global environmental change alters the production, terrestrial export, and photodegradation of organic carbon in northern lakes. Sedimentary biogeochemical records can provide a unique means to understand the nature of these changes over long time scales, where observational data fall short. We deployed in situ experiments on two shallow subarctic lakes with contrasting light regimes; a clear tundra lake and a dark woodland lake, to first investigate the photochemical transformation of carbon and nitrogen elemental (C/N ratio) and isotope (δ¹³C, δ¹⁵N) composition in lake water particulate organic matter (POM) for downcore inferences. We then explored elemental, isotopic, and spectral (inferred lake water total organic carbon [TOC] and sediment chlorophyll a [CHLa]) fingerprints in the lake sediments to trace changes in aquatic production, terrestrial inputs and photodegradation before and after profound human impacts on the global carbon cycle prompted by industrialization. POM pool in both lakes displayed tentative evidence of UV photoreactivity, reflected as increasing δ¹³C and decreasing C/N values. Through time, the tundra lake sediments traced subtle shifts in primary production, while the woodland lake carried signals of changing terrestrial contributions, indicating shifts in terrestrial carbon export but possibly also photodegradation rates. Under global human impact, both lakes irrespective of their distinct carbon regimes displayed evidence of increased productivity but no conspicuous signs of increased terrestrial influence. Overall, sediment biogeochemistry can integrate a wealth of information on carbon regulation in northern lakes, while our results also point to the importance of considering the entire spectrum of photobiogeochemical fingerprints in sedimentary studies.

全球环境变化改变了北部湖泊有机碳的生产、陆地输出和光降解。沉积生物地球化学记录可以提供一种独特的方法来了解这些变化在很长一段时间内的性质，而观测数据不足。我们在两个浅色亚北极湖泊上进行了原位实验，光照条件对比鲜明；一个清澈的苔原湖和一个黑暗的林地湖，首先研究碳和氮元素（C/N 比）和同位素（δ ¹³ C、δ ¹⁵ N）组成的光化学转化，用于下核的湖水颗粒有机物 (POM)推论。然后，我们探索了元素、同位素和光谱（推断的湖水总有机碳 [TOC] 和沉积物叶绿素a[CHLa]) 湖泊沉积物中的指纹，以追踪人类对工业化引发的全球碳循环产生深远影响之前和之后水生生产、陆地输入和光降解的变化。两个湖泊中的 POM 池都显示出紫外线光反应性的初步证据，反映为 δ ^{13 的}增加C 和递减的 C/N 值。随着时间的推移，苔原湖沉积物追踪初级生产的微妙变化，而林地湖携带着陆地贡献变化的信号，表明陆地碳输出的变化，但也可能是光降解率的变化。在全球人类影响下，无论其独特的碳状况如何，这两个湖泊都显示出生产力提高的证据，但没有明显迹象表明陆地影响增加。总体而言，沉积物生物地球化学可以整合关于北部湖泊碳调控的丰富信息，而我们的结果也表明在沉积研究中考虑整个光生物地球化学指纹谱的重要性。