Marcus Christl

Cosmogenic ¹⁰Be-based denudation rates have been widely used to explore potential controls on erosion such as tectonic uplift, periglacial conditions, precipitation gradients, bedrock erodibility, landslides, and hillslope morphology. However, there is a strong scale-dependency of the rates and the rate variability, particularly at the margin of mountain belts. Here, we explore such a scale dependency along a NW-SE section from the northern margin to the core of the Central European Alps. We present ¹⁰Be-derived denudation rates from 16 nested sub-catchments (2–340 km²) that we complement with 45 published ¹⁰Be concentrations, thereby covering the full range in scale and landscape properites that can be found at the margin of a mountain belt. We find that on a regional scale, the denudation rates strongly correlate with surface uplift, mean elevation and hillslope relief, but not with precipitation. Yet for basins that are smaller than 50 km ² , the denudation rates start to show a large variability deviating from the spatial trend, reflecting various controls. The variability in denudation rates becomes larger towards the core of the Alps where the uplift rates are high. Accordingly, uplift rates – and thus geodynamic processes – appear to exert the first-order controls on the denudation rate pattern and the landscape properties at the scale of the northern margin of the Central European Alps. Yet superimposed on this trend, we find that the variability in the landscape properties and the variability in the denudation rates become larger as the uplift rates increase and the studied basins becomes smaller.

The mechanisms controlling the long‐term preservation of widespread high‐elevation, low‐relief surfaces in active orogens remain poorly constrained. This is epitomized in the southeastern Tibetan Plateau, where extensive high‐elevation, low‐relief surfaces persist adjacent to deeply incised gorges despite intense fluvial incision. To decode their preservation and dissection, we quantify drainage‐divide migration along the margins of a representative high‐elevation low‐relief surface located near Yajiang by combining geomorphic analysis with newly acquired cosmogenic ¹⁰ Be‐derived erosion rates. Our results demonstrate that while drainage divides are actively migrating and dissecting the landscape, migration proceeds at slow rates (∼30–60 m/Myr) that effectively limit overall degradation and enable the long‐term persistence of low‐relief topography. In contrast, river capture can trigger rapid dissection through erosional wave propagation at rates exceeding those of divide migration, producing diachronous and piecemeal dissection across high‐elevation, low‐relief surfaces due to the stochastic occurrence of capture events. Numerical simulations further confirm that gradual divide migration remains slow over geologic timescales, whereas spontaneous river capture can rapidly accelerate high‐elevation, low‐relief surface degradation. Together, we propose that heterogeneous divide migration rates and divide jumps caused by river capture contribute to the irregular geometry of surviving high‐elevation, low‐relief surface remnants in the southeastern Tibetan Plateau.

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.

The oxygen isotope (δ ¹⁸ O _ice ) record from a ∼310-meter core drilled on the Guliya ice cap (GIC) in 2015 (GP2015) demonstrates reproducibility with a ∼309-meter core drilled nearby in 1992. Construction of the timescale for a composite of the GIC cores used ¹⁰ Be and ³⁶ Cl to locate the 41–thousand year Laschamp geomagnetic excursion and a match to a δ ¹⁸ O _atm -dated core from the Guliya Summit. Comparison of the δ ¹⁸ O record from an Asian Monsoon speleothem with the GIC δ ¹⁸ O _ice supports a timescale back to 128 thousand years, the oldest known so far from Tibet. The δ ¹⁸ O _ice record shows orbital variations in phase with June insolation and polar ice core stable isotope records through the last glacial cycle, although the relationship is reversed since the deglaciation. Future investigation is required to resolve this observation. Radiocarbon-dated ice from the glacier margin supports the presence of glacial-stage ice in the GIC. The ³⁶ Cl/ ¹⁰ Be ratios in GP2015 confirm that GIC ice is older than 100 thousand years.

The Carrington event of 1859 CE is considered one of the largest geomagnetic storms of the observational era and often used as a benchmark for a worst-case scenario. Yet, there exists no robust evidence of an associated solar energetic particle (SEP) event of a significant magnitude, based on measurements of cosmogenic radionuclides 10Be and 14C from ice cores and tree rings, respectively. In this study, we present two 36Cl records from Greenland with 2- and 4-year resolution from the EGRIP and NGRIP ice core sites, together with semi-annual 10Be data from EGRIP, as well as annual 10Be and 36Cl concentrations from the Dome Summit Site, Law Dome, East Antarctica. We observe no significant 36Cl concentration increase around 1859 CE in the three records. This allows us to rule out an extreme SEP event hitting Earth associated with the Carrington event in terms of fluence above 30 MeV. Based on these ice core 36Cl measurements, we can suggest two scenarios: (i) a soft SEP event with a maximum fluence above 30 MeV up to three times larger than any Space Age event or (ii) the possibility that there was no Earth-bound SEP event. This article is part of the Theo Murphy meeting issue ‘Radiocarbon and cosmic radiation events’.

A prominent rapid increase in radiocarbon from tree rings has been detected in 5259 BCE (7208 years BP). In this study, we present 10Be and 36Cl data from the NGRIP and the GRIP ice cores from Greenland, and the EDML ice core from Antarctica around the 14C excursion. The ice-core radionuclide data show an increase consistent with the occurrence of an extreme solar energetic particle (SEP) event. The 10Be data show the event was of a similar magnitude as the extreme SEP event of 7176 BCE (9125 years BP), in agreement with previously published 14C data. Using all ice-core radionuclide data, we show that the event was characterized by a fluence above 200 MeV comparable with that of other extreme SEP events detected in radionuclide records. In addition, the detection of the SEP event in both tree-ring and ice-core records provides an important time-marker to synchronize the ice-core and tree-ring chronologies. This article is part of the Theo Murphy meeting issue ‘Radiocarbon and cosmic radiation events’.

Rapid increases in cosmogenic isotopes in tree-ring and ice core records point to rare, extreme perturbations in the Heliosphere over the past millennia. Identifying additional radiocarbon spikes—so-called Miyake events—and replicating or refuting published candidate events have since become an international priority. Yet, at present there are large gaps, both in magnitude and understanding, between more frequent and lower-energy events identified in space-age measurements and larger rare events identified over the past 15 ka from palaeo archives. Here, we generate additional annually-resolved radiocarbon data for a few short intervals between 3–4 ka before present (BP, i.e. 1950 CE), where initial radiocarbon data suggest either an increase in radiocarbon production or alternatively significant noise arising from the scale of error on the radiocarbon measurement continuum. By performing multiple high-precision radiocarbon measurements per analysed tree-ring year on the same cellulose samples, we reduce uncertainties and thus increase the sensitivity for detecting potential events. In addition to refining the structure of radiocarbon time-series during the Holocene, our findings contribute to the identification and characterization of a likely Miyake-type event in approximately 3481 BP/1532 BCE, and suggest further work is needed to either confirm or refute possible events at approximately 3763 BP/1814 BCE (moderate confidence) and approximately 3060 BP/1111 BCE (low confidence). Initial carbon cycle modelling of these event candidates suggests that they are two times smaller than any other of the Miyake events identified and confirmed in paleoenvironmental data. We also discuss sources of variability and uncertainty in the tree-ring radiocarbon measurement continuum. Using conventional dendrochronological statistics on radiocarbon time-series, we show that dramatic increases in replication (50–100x) would allow datasets to capture 95% of the theoretical variance in the inter-annual to medium frequency domains and, thereby, advance quantification of solar, geomagnetic and carbon cycle variation in Holocene tree-ring records, such as potentially distinguishing high versus low amplitude Schwabe solar cycles over the past millennia. This calls for a big-science approach—more typical for the space sciences—to produce and analyse such high-precision paleoenvironmental records. This article is part of the Theo Murphy meeting issue ‘Radiocarbon and cosmic radiation events’.

Oxidative weathering of pyrite consumes O ₂ , generates dissolved sulfate (SO ₄ ²⁻ ) and acidifies carbonates to release CO ₂ to the ocean-atmosphere system. Mountain belts are hotspots of chemical weathering and geological carbon cycling, but understanding the net role of orogenesis in modulating the evolution of atmospheric CO ₂ and O ₂ levels requires robust constraints on weathering pathways such as pyrite oxidation. Sulfur and water-normalized oxygen isotopic compositions of riverine SO ₄ ²⁻ (δ ³⁴ S _{SO4 ²⁻} and Δ ¹⁸ O) are potentially powerful tracers to quantify pyrite oxidation, but they may be overprinted by microbial sulfate reduction (MSR)—a process often overlooked in terrestrial environments. To address this, we generated paired geomorphological, geochemical, and microbiological data from the headwaters of the Ganga River in the Himalayas. Our results indicate that MSR overprinting is maximized when low erosion rates are coupled to relatively low precipitation rates, revealing a landscape-mediated hydrological control on microbial terrestrial sulfur cycling. By applying this insight to global compilations of riverine δ ³⁴ S _{SO4 ²⁻} , Δ ¹⁸ O and major ion chemistry, we show that MSR overprinting leads to systematic shift in riverine sulfate isotopic signals, implying that global CO ₂ emissions and O ₂ consumption fluxes from pyrite weathering may be up to double previous isotope-based estimates.

Surface uplift is caused by a wide variety of mechanisms. Isolating the primary driver of regional uplift across continental margins can be difficult due to overlapping temporal and spatial signals and a lack of chronological constraints. In eastern Patagonia, hundreds of meters of late Cenozoic uplift have been inferred across the Golfo San Jorge, where the elevated glaciofluvial terraces of the Rodados Patagónicos record a history of uplift, incision and landscape degradation. Previous interpretations suggested Miocene/Pliocene terrace formation followed by a surface uplift attributed to long-wavelength dynamic topography associated with the subduction of the Chile Triple Junction. However, a lack of direct dating of the Rodados Patagónicos limits our ability to define an uplift history region primary mechanism. In this study, we apply cosmogenic 10Be dating of amalgamated cobble samples and depth profiles. Cobble dates samples are heavily dispersed and do not fit with the stratigraphy of the terraces, implying inheritance and limiting their reliability. However, depth profiles modeling provides robust ages of terrace abandonment, indicating formation between ca. 270 ka and ca. 80 ka. These results demonstrate that the Rodados Patagónicos are much younger than previously thought, consistent with the chronology of the Patagonian Ice Sheet. Combining terraces ages and elevations reveals rapid incision rates of 2.5 mm/yr, implying rapid uplift of the landscape. These rates are inconsistent with dynamic topography alone and instead support a model of thermal erosion of the lithospheric mantle below Patagonia, enhanced glacial exhumation of the surface. Our findings highlight the dominance of isostatic processes in driving rapid margin uplift and underscore the importance of well-constrained chronologies when distinguishing competing uplift mechanisms.