Maud Henrion

Upland peatlands are a major terrestrial carbon reservoir that may play an important role in the global carbon cycle. However, knowledge of upland peatlands before the Holocene remains speculative because of the poor long-term preservation potential of peat in upland environments. Here, we explore the use of paired ²⁶ Al and ¹⁰ Be to simultaneously determine denudation rates and peat thicknesses averaged over multiple glacial-interglacial cycles. We report cosmogenic ²⁶ Al and ¹⁰ Be concentrations in quartz from saprolite underlying the modern peat cover along a hillslope transect and from stream sediment in the Hautes Fagnes, an upland peatland in the Belgian Ardennes. The measured ²⁶ Al / ¹⁰ Be ratios are lower than expected for steady-state denudation under the modern peat cover, which we interpret as evidence of thicker peat in the past. To quantify long-term average peat thicknesses and denudation rates and identify secular changes in overburden, we inverse-model the measured ²⁶ Al and ¹⁰ Be concentrations. Modelled denudation rates of the saprolite, reflecting landscape lowering rates, are exceptionally low (0.3–4.9 tons km ⁻² yr ⁻¹ , equivalent to approximately 0.1–1.9 m Myr ⁻¹ ). The median probability long-term overburden thicknesses exceed modern overburden thicknesses by 190–350 g cm ⁻² along the hillslope transect, approximately equivalent to 1.8–3.4 m of saturated peat. Peat degradation from historical land use, including peat extraction, drainage, and afforestation, may explain much of the discrepancy. Inverse modeling of the sample with the slowest denudation rate, and thus the longest near-surface residence time of quartz and signal integration timescale, suggests that a secular increase in overburden thickness, potentially reflecting the onset of peat cover, coincided with mid-Pleistocene uplift of the Ardennes. These results demonstrate the utility of cosmogenic nuclides in inferring the long-term history of peat cover where geomorphic process rates are slow and differential radioactive decay is non-negligible.

Upland peatlands are a major terrestrial carbon reservoir that may play an important role in the global carbon cycle. However, knowledge of upland peatlands before the Holocene remains speculative because of the poor long-term preservation potential of peat in upland environments. Here, we explore using paired ²⁶Al and ¹⁰Be to simultaneously determine denudation rates and peat thicknesses averaged over multiple glacial-interglacial cycles. We report cosmogenic ²⁶Al and ¹⁰Be concentrations in quartz from saprolite underlying the modern peat cover along a hillslope transect and from stream sediment in the Hautes Fagnes, an upland peatland in the Belgian Ardennes. The measured ²⁶Al/¹⁰Be ratios are lower than expected for steady-state denudation under the modern peat cover, which we interpret as evidence of thicker peat in the past. To quantify long-term average peat thicknesses and denudation rates and identify secular changes in overburden, we inverse-model the measured ²⁶Al and ¹⁰Be concentrations. Modeled denudation rates of the saprolite, reflecting landscape lowering rates, are exceptionally low (0.3–4.9 tons km^-2 yr^-1, equivalent to approximately 0.1–1.9 m Myr^-1). The median probability long-term overburden thicknesses exceed modern overburden thicknesses by 190–350 g cm^-2 along the hillslope transect, approximately equivalent to 1.8–3.4 m of saturated peat. Peat degradation from historical land use, including peat extraction, drainage, and afforestation, may explain much of the discrepancy. Inverse-modeling of the sample with the slowest denudation rate, and thus the longest near-surface residence time of quartz and signal integration timescale, suggests that a secular increase in overburden thickness, potentially reflecting the onset of peat cover, coincided with mid-Pleistocene uplift of the Ardennes. These results demonstrate the utility of cosmogenic nuclides in inferring the long-term history of peat cover where geomorphic process rates are slow and differential radioactive decay is non-negligible.

Upland peatlands are a major terrestrial carbon reservoir that may play an important role in the global carbon cycle. However, knowledge of upland peatlands before the Holocene remains speculative because of the poor long-term preservation potential of peat in upland environments. Here, we explore using paired ²⁶Al and ¹⁰Be to simultaneously determine denudation rates and peat thicknesses averaged over multiple glacial-interglacial cycles. We report cosmogenic ²⁶Al and ¹⁰Be concentrations in quartz from saprolite underlying the modern peat cover along a hillslope transect and from stream sediment in the Hautes Fagnes, an upland peatland in the Belgian Ardennes. The measured ²⁶Al/¹⁰Be ratios are lower than expected for steady-state denudation under the modern peat cover, which we interpret as evidence of thicker peat in the past. To quantify long-term average peat thicknesses and denudation rates and identify secular changes in overburden, we inverse-model the measured ²⁶Al and ¹⁰Be concentrations. Modeled denudation rates of the saprolite, reflecting landscape lowering rates, are exceptionally low (0.3–4.9 tons km^-2 yr^-1, equivalent to approximately 0.1–1.9 m Myr^-1). The median probability long-term overburden thicknesses exceed modern overburden thicknesses by 190–350 g cm^-2 along the hillslope transect, approximately equivalent to 1.8–3.4 m of saturated peat. Peat degradation from historical land use, including peat extraction, drainage, and afforestation, may explain much of the discrepancy. Inverse-modeling of the sample with the slowest denudation rate, and thus the longest near-surface residence time of quartz and signal integration timescale, suggests that a secular increase in overburden thickness, potentially reflecting the onset of peat cover, coincided with mid-Pleistocene uplift of the Ardennes. These results demonstrate the utility of cosmogenic nuclides in inferring the long-term history of peat cover where geomorphic process rates are slow and differential radioactive decay is non-negligible.

Upland peatlands are a major terrestrial carbon reservoir that may play an important role in the global carbon cycle. However, knowledge of upland peatlands before the Holocene remains speculative because of the poor long-term preservation potential of peat in upland environments. Here, we explore using paired ²⁶Al and ¹⁰Be to simultaneously determine denudation rates and peat thicknesses averaged over multiple glacial-interglacial cycles. We report cosmogenic ²⁶Al and ¹⁰Be concentrations in quartz from saprolite underlying the modern peat cover along a hillslope transect and from stream sediment in the Hautes Fagnes, an upland peatland in the Belgian Ardennes. The measured ²⁶Al/¹⁰Be ratios are lower than expected for steady-state denudation under the modern peat cover, which we interpret as evidence of thicker peat in the past. To quantify long-term average peat thicknesses and denudation rates and identify secular changes in overburden, we inverse-model the measured ²⁶Al and ¹⁰Be concentrations. Modeled denudation rates of the saprolite, reflecting landscape lowering rates, are exceptionally low (0.3–4.9 tons km^-2 yr^-1, equivalent to approximately 0.1–1.9 m Myr^-1). The median probability long-term overburden thicknesses exceed modern overburden thicknesses by 190–350 g cm^-2 along the hillslope transect, approximately equivalent to 1.8–3.4 m of saturated peat. Peat degradation from historical land use, including peat extraction, drainage, and afforestation, may explain much of the discrepancy. Inverse-modeling of the sample with the slowest denudation rate, and thus the longest near-surface residence time of quartz and signal integration timescale, suggests that a secular increase in overburden thickness, potentially reflecting the onset of peat cover, coincided with mid-Pleistocene uplift of the Ardennes. These results demonstrate the utility of cosmogenic nuclides in inferring the long-term history of peat cover where geomorphic process rates are slow and differential radioactive decay is non-negligible.

Permafrost is degrading, raising concerns about its impact on global climate. Taliks, year-round unfrozen layers of ground in permafrost environments, affect Arctic hydrological and carbon dynamics and contribute to permafrost degradation. Despite their importance, they are seldom studied because of the difficulty in identifying them. Water tracks (zones overlying permafrost concentrating water flow) have an important role in controlling catchment hydrology, yet their contribution to talik formation remains poorly understood. The objective of this study is to detect and characterize suprapermafrost taliks in three-dimensions at high spatial resolution (dm-scale), with a specific focus on those located beneath water tracks. Fieldwork was conducted in a discontinuous permafrost area near Eight Mile Lake, Alaska (USA), during winter using a Ground-penetrating radar with a 600 MHz antenna. Ground-penetrating radar proved to be a reliable tool for imaging talik depth and extent. While talik tops were clearly detected with a root mean square error of 17 cm, their bottoms were less identifiable due to limited signal penetration. Both isolated and lateral suprapermafrost taliks were observed at the site. Importantly, taliks were more present, shallower and thicker in water tracks than in their adjacent areas. Additionally, thicker snow cover and topographic depressions were significantly associated with shallower taliks (respective significant correlations of -0.65 and 0.53). Water tracks thus appear to be hotspots for talik formation and expansion, with important implications for winter subsurface hydrological connectivity. These findings highlight the need for increased attention to the processes occurring during the winter in the water tracks environments.

Upland peatlands are a major terrestrial carbon reservoir that may play an important role in the global carbon cycle. However, knowledge of upland peatlands before the Holocene remains speculative because of the poor long-term preservation potential of peat in upland environments. Here, we explore using paired 26Al and 10Be to simultaneously determine denudation rates and peat thicknesses averaged over multiple glacial-interglacial cycles. We report cosmogenic 26Al and 10Be concentrations in quartz from saprolite underlying the modern peat cover along a hillslope transect and from stream sediment in the Hautes Fagnes, an upland peatland in the Belgian Ardennes. The measured 26Al/10Be ratios are lower than expected for steady-state denudation under the modern peat cover, which we interpret as evidence of thicker peat in the past. To quantify long-term average peat thicknesses and denudation rates and identify secular changes in overburden, we inverse-model the measured 26Al and 10Be concentrations. Modeled denudation rates of the saprolite, reflecting landscape lowering rates, are exceptionally low (0.3–4.9 tons km-2 yr-1, equivalent to approximately 0.1–1.9 m Myr-1). The median probability long-term overburden thicknesses exceed modern overburden thicknesses by 190–350 g cm-2 along the hillslope transect, approximately equivalent to 1.8–3.4 m of saturated peat. Peat degradation from historical land use, including peat extraction, drainage, and afforestation, may explain much of the discrepancy. Inverse-modeling of the sample with the slowest denudation rate, and thus the longest near-surface residence time of quartz and signal integration timescale, suggests that a secular increase in overburden thickness, potentially reflecting the onset of peat cover, coincided with mid-Pleistocene uplift of the Ardennes. These results demonstrate the utility of cosmogenic nuclides in inferring the long-term history of peat cover where geomorphic process rates are slow and differential radioactive decay is non-negligible.

Permafrost is degrading, raising concerns about its impact on global climate. Taliks, year-round unfrozen layers of ground in permafrost environments, affect Arctic hydrological and carbon dynamics and contribute to permafrost degradation. Despite their importance, they are seldom studied because of the difficulty in identifying them. Water tracks (zones overlying permafrost concentrating water flow) have an important role in controlling catchment hydrology, yet their contribution to talik formation remains poorly understood. The objective of this study is to detect and characterize suprapermafrost taliks in three-dimensions at high spatial resolution (dm-scale), with a specific focus on those located beneath water tracks. Fieldwork was conducted in a discontinuous permafrost area near Eight Mile Lake, Alaska (USA), during winter using a Ground-penetrating radar with a 600 MHz antenna. Ground-penetrating radar proved to be a reliable tool for imaging talik depth and extent. While talik tops were clearly detected with a root mean square error of 17 cm, their bottoms were less identifiable due to limited signal penetration. Both isolated and lateral suprapermafrost taliks were observed at the site. Importantly, taliks were more present, shallower and thicker in water tracks than in their adjacent areas. Additionally, thicker snow cover and topographic depressions were significantly associated with shallower taliks (respective significant correlations of -0.65 and 0.53). Water tracks thus appear to be hotspots for talik formation and expansion, with important implications for winter subsurface hydrological connectivity. These findings highlight the need for increased attention to the processes occurring during the winter in the water tracks environments.

Permafrost is degrading, raising concerns about its impact on global climate. Taliks, year-round unfrozen layers of ground in permafrost environments, affect Arctic hydrological and carbon dynamics and contribute to permafrost degradation. Despite their importance, they are seldom studied because of the difficulty in identifying them. Water tracks (zones overlying permafrost concentrating water flow) have an important role in controlling catchment hydrology, yet their contribution to talik formation remains poorly understood. The objective of this study is to detect and characterize suprapermafrost taliks in three-dimensions at high spatial resolution (dm-scale), with a specific focus on those located beneath water tracks. Fieldwork was conducted in a discontinuous permafrost area near Eight Mile Lake, Alaska (USA), during winter using a Ground-penetrating radar with a 600 MHz antenna. Ground-penetrating radar proved to be a reliable tool for imaging talik depth and extent. While talik tops were clearly detected with a root mean square error of 17 cm, their bottoms were less identifiable due to limited signal penetration. Both isolated and lateral suprapermafrost taliks were observed at the site. Importantly, taliks were more present, shallower and thicker in water tracks than in their adjacent areas. Additionally, thicker snow cover and topographic depressions were significantly associated with shallower taliks (respective significant correlations of -0.65 and 0.53). Water tracks thus appear to be hotspots for talik formation and expansion, with important implications for winter subsurface hydrological connectivity. These findings highlight the need for increased attention to the processes occurring during the winter in the water tracks environments.