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Publications1 - 10 of 14

Rock slope temperature evolution and micrometer-scale deformation at a retreating glacier margin
Hugentobler, Marc; Aaron, Jordan; Loew, Simon (2021)
ESS Open Archive
In deglaciating environments, rock mass weakening and potential formation of rock slope instabilities is driven by long-term and seasonal changes in thermal- and hydraulic boundary conditions, combined with unloading due to ice melting. However, in-situ observations are rare. In this study, we present new monitoring data from three highly instrumented boreholes, and numerical simulations to investigate rock slope temperature evolution and micrometer-scale deformation during deglaciation. Our results show that the subsurface temperatures are adjusting to a new, warmer surface temperature following ice retreat. Heat conduction is identified as the dominant heat transfer process at sites with intact rock. Observed nonconductive processes are related to groundwater exchange with cold subglacial water, snowmelt infiltration, or creek water infiltration. Our strain data shows that annual surface temperature cycles cause thermoelastic deformation that dominate the strain signals in the shallow thermally active layer at our stable rock slope locations. At deeper sensors, reversible strain signals correlating with pore pressure fluctuations dominate. Irreversible deformation, which we relate with progressive rock mass damage, occurs as short-term (hours to weeks) strain events and as slower, continuous strain trends. The majority of the short-term irreversible strain events coincides with precipitation events or pore pressure changes. Longer-term trends in the strain time series and a minority of short-term strain events cannot directly be related to any of the investigated drivers, but changes of glacial loading and fatigue processes are considered as potential causes.
Late Oligocene midlatitude warming and temperate Early Miocene from alkenone-derived Sea Surface Temperature estimates
Guitián, José; Stoll, Heather (2021)
ESS Open Archive
Large Antarctic ice volume changes characterized the middle to Late Oligocene and the first million years of climate evolution during the Miocene. However, the sea surface temperature (SST) evolution over this period remains poorly constrained, as only a few records from contrasting proxies are available. In this study, we present a long-term alkenone-derived SST record from sediments drilled by the Ocean Drilling Program (ODP) at Site 1168 in the west Tasmanian Sea spanning 29.8 Ma to 16.7 Ma. The SST record reaffirms that the long term warming in the Late Oligocene linked to the end of the Middle Oligocene Glacial Interval can be recognized also at mid-to-high latitudes of the Southern Hemisphere. Stable average temperatures are present from 24.5 to 22 Ma, and then decrease 2°C into the Miocene until they stabilize by 20.1 Ma. The reconstructed temperatures are highly variable in the warm Late Oligocene waters, and more stable and slightly colder in the Early to Middle Miocene. We confirm that this temperature trend is not an artefact of the latitudinal drift of the site, as the temperature anomaly relative to the modern water temperature at the paleolocation confirms the SST trends of the Oligocene. This is the first alkenone-derived record to show the cold conditions related with the Middle Oligocene Glacial Interval in the Southern Ocean and gradual warming in the latest Oligocene.
Global Frictional Equilibrium via Stochastic, Local Coulomb Frictional Slips
Zhang, Shihuai; Ma, Xiaodong (2020)
ESS Open Archive
Natural variability of fault friction and slip uncertainty exist in the Earth’s crust. To what extent it influences crustal stress and its evolution is intriguing. We established a quasi-static, 2D model to simulate the stress evolution due to Coulomb frictional slips in the brittle crust. The model simply features randomly-oriented fractures with heterogeneous frictional coefficients. We emphasized the global stress response by summing the contribution of cascades of local frictional slip under specific boundary conditions. We illustrated that the decrease in stress difference manifests as a self-organized process that ultimately leads to frictional equilibrium. The model informs that the frictional equilibrium of a stochastic system can depart substantially from a deterministic estimation. Although the model quantitatively corroborates the notion of frictional equilibrium in places where fracture slip is the dominant mechanism for stress release, it reveals far more profound influence of system heterogeneity on the local and global stress evolution.
Scale-aware evaluation of complex mountain boundary layer flow from observations and simulations
Goger, Brigitta; Lapo, Karl (2025)
ESS Open Archive
Boundary layers over complex, mountainous terrain are characterized by multi-scale, complex flow structures, where scale separation poses a fundamental challenge. In this study, we apply the novel multiresolution coherent spatio-temporal scale separation (mrCOSTS) method to LIDAR observations and numerical data of the velocity components of complex mountain boundary-layer flow. We are able to identify three distinct time scales (i.e., turbulent scales, mountain boundary layer, and diurnal scales) and explore the underlying physical processes. Furthermore, we identified the dominant flow patterns for each time scale, e.g., down- and up-valley flows, cross-valley vortices, small-scale turbulence, and large evening transition eddies . Applying mrCOSTS to simulated velocity components enables us to identify how coherent structures and the flow patterns are represented at various mesh sizes in the model. Using mrCOSTS we trivially retrieved complex dynamics that were previously difficult to resolve, enabling a direct, scale-aware evaluation between the LIDAR observations and model results.
Micro-Meteorological Impact of Glacier Retreat and Proglacial Lake Temperature in Western Norway
Flacké Haualand, Kristine; Sauter, Tobias; Abermann, Jakob; et al. (2024)
ESS Open Archive
Glaciers are retreating worldwide, yet, little is known about the influence of these changes on local weather and climate in glacial landscapes. Changes in glacier extent and proglacial lakes alter the thermodynamic forcing in glacier-lake-valley systems that may be of similar or greater importance for future microclimate than direct effects of global warming. To study the impact of these changes, we combine the first set of high-density spatiotemporal observations of a glacier-lake-valley system at Nigardsbreen in western Norway with high-resolution numerical simulations from the Weather Research and Forecasting (WRF) model. The sensitivity of the thermodynamic circulation to glacier extent and proglacial lakes is tested using glacier outlines from 2006 and 2019 as well as varying lake surface temperature. The model represents the evolution of glacier flow and cold air pools well when thermal forcing dominates over large-scale forcing. During a persistent down-glacier flow regime, the glacier-valley circulation is sensitive to lake temperature and glacier extent, with strong impacts on wind speed, convection in the valley, and interaction with mountain waves. However, when the large-scale forcing dominates and the down-glacier flow is weak and shallower, impacts on atmospheric circulation are smaller, especially those related to lake temperature. This high sensitivity to meteorological conditions is related to whether the flow regime promotes thermal coupling between the glacier and the lake. The findings of this study highlight the need for accurate representation of glacier extent and proglacial lakes when evaluating local effects of past and future climate change in glacierized regions.
CO 2 uptake in the Pacific from 1985 to 2018: a comparative assessment of observation-and model-based estimates
Ishii, Masao; Carter, Brendan R.; Toyama, Katsuya; et al. (2024)
ESS Open Archive
As a contribution to the second REgional Carbon Cycle Assessment and Processes effort, we compare net and anthropogenic sea-to-air CO2 fluxes, CO2 accumulation rates in the ocean interior and their trends in the Pacific Ocean by analyzing results from state-of-the-art observation-based estimates and global ocean biogeochemistry models (GOBMs) over the period 1985 – 2018. The ensemble-mean net CO2 fluxes integrated over the Pacific (44ºS – 62ºN) are -0.41 ±0.12 PgC yr-1 from pCO2 products and -0.51 ±0.16 PgC yr-1 from GOBMs. The anthropogenic CO2 flux from GOBMs (-0.71 ±0.10 PgC yr-1) is 1.4 times as large as the net CO2 flux, with particularly large uptake in the equatorial region (-0.34 ±0.03 PgC yr-1) largely offsetting the large natural CO2 outgassing there (+0.72 ±0.06 PgC yr-1). The basin-wide net CO2 uptake has increased at similar mean rates of -0.088 ±0.062 and -0.079 ±0.016 PgC yr-1 decade-1 in pCO2 products and GOBMs, respectively, comparable with the rate of increase in anthropogenic CO2 uptake at -0.102 ±0.013 PgC yr-1 decade-1 in GOBMs. However, a notable mismatch in the trend of the net CO2 flux change that exists between pCO2 products (+0.001 ±0.020 PgC yr-1 decade-1) and GOBMs (-0.040 ±0.013 PgC yr-1 decade-1) in the equatorial region is yet to be resolved. The rate of anthropogenic CO2 accumulation from GOBMs is +0.76 ±0.17 PgC yr-1. This is nearly balanced with the anthropogenic CO2 flux and is also encompassed by the previous observation-based estimates. But a better consistency is still required in the South Pacific
Clumped isotope temperatures of coccolithophores from global sediment traps
Clark, Alexander Johannes; Jaggi, Madalina; Bernasconi, Stefano M.; et al. (2024)
ESS Open Archive
Temperature proxies such as clumped isotope (Δ47) thermometry on biogenic carbonates are applied to the past with greatest confidence when the proxy-temperature relationship is shown to be robust within natural temperature conditions of the ocean. Especially well-suited for this purpose are biogenic carbonates sampled from well-constrained production period and oceanographic conditions of sediment traps. Since coccolithophorids have a cosmopolitan distribution and are major biogenic carbonate producers in the surface ocean, their coccoliths usually dominate the inorganic carbon flux in sediment traps and are sufficiently abundant in most traps for clumped isotope analysis. Here, we measured Δ47 in the coccolith size fraction of 18 sediment trap samples across a 75° latitudinal gradient and three ocean basins. To identify the upper ocean provenance region of the coccoliths in each trap, a simple model of coccolith transport by ocean currents was constructed. The coccolith Δ47 strongly follows the upper ocean temperatures, in particular the average temperatures from the maximum production depths of living coccolithophores from their provenance areas. There is no evidence for a coccolithophore species-specific effect on the Δ47-temperature relationship. Applying the recent coccolith-specific Δ47-temperature calibration (Clark et al., 2024a) to estimate calcification temperatures shows that inferred calcification depths match the depth of maximum coccolithophore production in the provenance area. Compared to other calibrations for biogenic carbonates, the coccolith-specific Δ47-temperature calibration yields the best agreement with the depth of maximum coccolithophore abundance and the expected depth of coccolith production.
Constraining greenhouse gas cycling and emissions in Africa's largest humic lake
Barthel, Matti; de Clippele, Antoine; de Groot, Lissie W.; et al. (2025)
ESS Open Archive
Humic tropical lakes and wetlands are globally important sources of atmospheric greenhouse gases (GHGs). However, mechanistic insight into GHG cycling in such systems remains limited—especially in understudied central Africa. To address this, here we measured wet- and dry-season concentrations and isotopic compositions of the major dissolved GHGs CO2, CH4, and N2O in Africa’s largest humic lake: Mai Ndombe, Democratic Republic of Congo. We find that the water column is highly supersaturated with respect to atmospheric equilibrium for all GHGs across all seasons, sampling stations, and water depths. Additionally, all GHG concentrations increase with increasing water depth, reflecting atmospheric gas exchange due to physical mixing in the upper water column as well as biological processes. Extrapolating these results—combined with field measurements such as temperature and wind speed—we estimate that Lake Mai Ndombe emits 408±27 Gg C yr-1 as CO2, 695±146 Mg C yr-1 as CH4, and 213±13 Mg N yr-1 as N2O (μ±1σ propagated Monte Carlo uncertainty). Furthermore, carbon-isotope signals indicate that CO2 is sourced from rapid respiration of bioavailable organic carbon, whereas CH4 reflects sedimentary methanogenesis followed by aerobic methanotrophy in the water column. Finally, N2O bulk and position-specific isotopic compositions reveal a nitrogen cycle dominated by sedimentary denitrification, with near-quantitative reduction to N2 prior to upward diffusion into the water column and eventual outgassing. Combined, these observations imply that small perturbations to carbon inputs, water-column thickness, and/or dissolved oxygen saturation would likely have profound impacts on the flux and composition of GHGs emitted from tropical humic lakes.
Controls on spatial and temporal patterns of slope deformation in a paraglacial environment
Oestreicher, Nicolas; Loew, Simon; Roques, Clément; et al. (2021)
ESS Open Archive
A comprehensive surface displacement monitoring system installed in the recently deglaciated bedrock slopes of the Aletsch Valley shows systematic reversible motions at the annual scale. We explore potential drivers for this deformation signal and demonstrate that the main driver is pore pressure changes of phreatic groundwater in fractured granitic mountain slopes. The spatial pattern of these reversible annual deformations shows similar magnitudes and orientations for adjacent monitoring points, leading to the hypothesis that the annually reversible deformation is caused by slope-scale groundwater elevation changes and rock mass properties. Conversely, we show that the ground reaction to infiltration from snowmelt and summer rainstorms can be highly heterogeneous at local scale, and that brittle-ductile fault zones are key features for the groundwater pressure-related rock mass deformations. We also observe irreversible long-term trends (over the 6.5 yr dataset) of deformation in the Aletsch valley composed of a larger uplift than observed at our reference GNSS station in the Rhone valley, and horizontal displacements of the slopes towards the valley. These observations can be attributed respectively to the elastic bedrock rebound in response to current glacier mass downwasting of the Great Aletsch Glacier and gravitational slope deformations enabled by cyclic groundwater pressure-related rock mass fatigue in the fractured rock slopes.
Precise kinetic parameters for thermal resetting of clumped-isotope signatures in biogenic and abiogenic calcites
Kueter, Nico; Looser, Nathan; Hemingway, Jordon; et al. (2025)
ESS Open Archive
Carbonate clumped-isotope (∆47) thermometry is a powerful tool to reconstruct paleotemperatures. However, episodes of heating or cooling can alter original ∆47 values through diffusive C-O bond reordering by isotopic exchange between neighboring carbonate groups within the mineral lattice and/or oxygen isotope exchange between carbonate groups and water (collectively termed “thermal resetting”). Nevertheless, if precise kinetic constraints are available, altered ∆47 values can be utilized to reconstruct thermal burial histories of sedimentary basins or to restore primary ∆47 values from carbonates which experienced thermal resetting in their geological history. Here we present new high-resolution heating experiments on optical (abiogenic) and belemnite (biogenic) calcite. By capturing early signals, we derive new precise disordered kinetic parameters for both materials [optical calcite: µE = 216.47 ± 6.95 kJ mol-1, sE = 14.51 ± 1.22 kJ mol-1, and v0 = 28.61 ± 1.12 ln(min)-1; belemnite calcite: µE = 180.15 ± 7.94 kJ mol-1, sE = 22.24 ± 2.62 kJ mol-1, and v0 = 27.76 ± 1.43 ln(min)-1]. We present new FTIR data confirming the importance of intracrystalline water and organic matter on the faster thermal resetting observed for belemnite calcite. Complementary “snapshot” experiments on a diverse suite of materials reveal a systematic difference in reordering behavior between biogenic and abiogenic calcites, highlighting the importance of structural and compositional characteristics in controlling reordering kinetics. These snapshot experiments can complement petrographic and geochemical methods in assessing the pristine nature of calcite samples and provide guidance for selecting the appropriate kinetic parameters for thermal modeling of different calcites.

Publications1 - 10 of 14

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