Abstract
Widespread ecological reorganizations and increases in organic carbon (OC) in lakes across the Northern Hemisphere have raised concerns about the impact of the ongoing climate warming on aquatic ecosystems and carbon cycling. We employed diverse biogeochemical techniques on a high-resolution sediment record from a subarctic lake in northern Finland (70°N) to examine the direction, magnitude and mechanism of change in aquatic carbon pools prior to and under the anthropogenic warming. Coupled variation in the elemental and isotopic composition of the sediment and a proxy-based summer air temperature reconstruction tracked changes in aquatic production, depicting a decline during a cool climate interval between ~1700–1900 C.E. and a subsequent increase over the 20th century. OC accumulation rates displayed similar coeval variation with temperature, mirroring both changes in aquatic production and terrestrial carbon export. Increase in sediment organic content over the 20th century together with high inferred aquatic UV exposure imply that the 20th century increase in OC accumulation is primarily connected to elevated lake production rather than terrestrial inputs. The changes in the supply of autochthonous energy sources were further reflected higher up the benthic food web, as evidenced by biotic stable isotopic fingerprints.
Highlights
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Previous studies have discerned warm temperature anomalies during the Middle Ages followed by a cool climate interval referred to as the ‘Little Ice Age’ (LIA) that marked the culmination of the Neoglacial cooling[1,18,19]
We propose that the synchronous variation of temperature with the stable isotopic composition and C/N ratio of the sediment elucidates primarily changes in the relative contribution of autochthonous and allochthonous organic matter
Summary
All material supplied via JYX is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. Recent research has demonstrated widespread increases in the concentrations of dissolved organic carbon (DOC) in lake waters across the Northern Hemisphere[6,7], as well as increases in sediment organic content over the 20th century[8,9,10]. These changes in aquatic carbon dynamics have profound effects on lake ecosystem functioning and metabolism[11,7], yet no scientific consensus exists on the mediating role of the anthropogenic warming. The results build towards an improved understanding of the influence of global change on aquatic carbon dynamics in northern lakes that constitute an integral element in the global carbon cycle
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