Journal of Geophysical Research: Earth Surface最新文献

Recent studies have revealed the presence of a complex freshwater system underlying the Aurora Subglacial Basin (ASB), a region of East Antarctica that contains ∼7 m of global sea level potential in ice mainly grounded below sea level. However, the impact that subglacial freshwater has on driving the evolution of the dynamic outlet glaciers that drain this basin has yet to be tested in a coupled ice sheet-subglacial hydrology numerical modeling framework. Here, we project the evolution of the primary outlet glaciers draining the ASB (Moscow University Ice Shelf, Totten, Vanderford, and Adams Glaciers) in response to an evolving subglacial hydrology system and to ocean forcing through 2100, following low and high CMIP6 emission scenarios. By 2100, ice-hydrology feedbacks enhance the ASB's 2100 sea level contribution by ∼30% (7.50–9.80 mm) in high emission scenarios and accelerate the retreat of Totten Glacier's main ice stream by 25 years. Ice-hydrology feedbacks are particularly influential in the retreat of the Vanderford and Adams Glaciers, driving an additional 10 km of retreat in fully coupled simulations relative to uncoupled simulations. Hydrology-driven ice shelf melt enhancements are the primary cause of domain-wide mass loss in low emission scenarios, but are secondary to ice sheet frictional feedbacks under high emission scenarios. The results presented here demonstrate that ice-subglacial hydrology interactions can significantly accelerate retreat of dynamic Antarctic glaciers and that future Antarctic sea level assessments that do not take these interactions into account might be severely underestimating Antarctic Ice Sheet mass loss.

Bedrock river incision drives the evolution of the Earth's landscape and is influenced by river hydraulic power. However, the relationship between plunging flows and the curvature of bedrock canyons is poorly understood, which encouraged us to explore how the bend's curvature and undulating beds affect plunging flows. A generalized physical model was built to investigate the hydrodynamic characteristics of plunging flows in a constant curvature flume with plain and undulating beds. Our experimental findings demonstrated that plunging flows were related to secondary circulation, topography, and width-to-depth ratios. Plunging flows occurred when secondary circulation reached its peak, and as secondary circulation vanished, the intensity of plunging flows decreased. The undulating bed topography in the bedrock bends suppressed secondary circulation and the development of plunging flows. Bed topography may be a dominant factor in plunging flows in bedrock bends. The potential erosion area in bedrock bends was related to the intensity of plunging flows, which caused velocity inversion to increase the shear stress near the bed. With higher discharges and undulating beds, the intensity of the transverse shear stress of the riverbed near the center was greater. The potential erosion area in bedrock bends was concentrated at the center of the cross-section around the bend apex upstream. Our experimental results can improve incision models in terms of the distribution of shear stress and flow structure in bedrock bends.

Forests overlap with large parts of the northern hemisphere permafrost area, and representing canopy processes is therefore crucial for simulating thermal and hydrological conditions in these regions. Forests impact permafrost through the modulation of radiative fluxes and exchange of turbulent fluxes, precipitation interception and regulation of transpiration. Forests also feature distinct soil layers of litter and organic matter, which play central roles for the infiltration and evaporation of water, while also providing thermal insulation for deeper ground layers. In this study, we present a new module within the CryoGrid community model to simulate forest ecosystems and their impact on the surface water and energy balance. The module includes a big-leaf vegetation scheme with adaptations for canopy heat storage and transpiration. Furthermore, we account for the effect of surface litter layers on water and energy transfer. We show that the model is capable of simulating radiation, snow cover and ground temperatures below a deciduous needleleaf forest on a north-facing slope in the Khentii Mountains in Central Mongolia. A sensitivity analysis of topographic aspect and ecosystem configuration confirms the important role of the litter layers for the energy and water balance of the ground. Furthermore, it suggests that the presence of permafrost is primarily linked to topographic aspect rather than the presence of forest at this site. The presented model scheme can be used to study the development of the ground thermal regime in forests, including the state of permafrost, under different climate, ecosystem, and land use scenarios.

The thermal field within the firn layer on the Greenland Ice Sheet (GrIS) governs meltwater retention processes, firn densification with surface elevation change, and heat transfer from the surface boundary to deep ice. However, there are few observational data to constrain these processes with only sparse in situ temperature time series that does not extend through the full firn depth. Here, we quantify the thermal structure of Western Greenland’s firn column using instrumentation installed in an elevation transect of boreholes extending to 30 and 96 m depth. During the high-melt summer of 2019, heat gain in the firn layer showed strong elevation dependency, with greater uptake and deeper penetration of heat at lower elevations. The bulk thermal conductivity increased by 15% per 100 m elevation loss due to higher density related to ice layers. Nevertheless, the conductive heat gain remained relatively constant along the transect due to stronger temperature gradients in the near surface firn at higher elevations. The primary driver of heat gain during this high melt summer was latent heat transfer, which increased up to ten-fold over the transect, growing by 34 MJ m⁻² per 100 m elevation loss. The deep-firn temperature gradient beneath the seasonally active layer doubled over a 270-m elevation drop across the study transect, increasing heat flux from the firn layer into deep ice at lower elevations. Our in situ firn temperature time series offers observational constraints for modeling studies and insights into the future evolution of the percolation zone in a warmer climate.

Land-ice flow in Antarctica has experienced multi-annual acceleration in response to increased rates of ice thinning, ice-shelf collapse and grounding-line retreat. Superimposed upon this trend, recent observations have revealed that land-ice flow in the Antarctic Peninsula exhibits seasonal velocity variability with distinct summertime speed-ups. The mechanism, or mechanisms, responsible for driving this seasonality are unconstrained at present, yet detailed, process-based understanding of such forcing will be important for accurately estimating Antarctica's future contributions to sea level. Here, we perform time-series analysis on an array of remotely sensed, modeled and reanalysis data sets to examine the influence of potential drivers of ice-flow seasonality in the Antarctic Peninsula. We show that both meltwater presence and ocean temperature act as statistically significant precursors to summertime ice-flow acceleration, although each elicits an ice-velocity response after a distinct lag, with the former prompting a more immediate response. Furthermore, we find that the timing and magnitude of these local drivers are influenced by large-scale climate phenomena, namely the Amundsen Sea Low and the El Niño Southern Oscillation, with the latter initiating an anomalous wintertime ice-flow acceleration event in 2016. This hitherto unidentified link between seasonal ice flow and large-scale climatic forcing may have important implications for ice discharge at and beyond the Antarctic Peninsula in the future, depending upon how the magnitude, frequency and duration of such climate phenomena evolve in a warming world.

Sources and fluxes of methane to the atmosphere from permafrost are significant but poorly constrained in global climate models. We present data collected from the variable permafrost setting of the outer Mackenzie River Delta, including observations of aquatic methane seepage, core determinations of in situ methane occurrence and seep gas isotope geochemistry. The sources and locations of in situ geologic methane occurrence and aquatic and atmospheric gas release appear to be controlled by the regional geology and permafrost conditions. Where permafrost is >250 m thick, thermogenic gas deposits at depth are isolated by laterally continuous, low permeability ice-bearing sediments with few through-going thawed taliks. Thus, the observed in situ methane and aquatic gas seepage appears to be dominated by microbial methane. In contrast, where permafrost is <80 m thick, taliks are more likely to be through-going, providing permeable conduits from depth and migration pathways for both thermogenic and biogenic gas. Continuous annual fluid sampling of two lakes and a river channel documents aquatic methane flux from microbial sources, more deeply buried thermogenic sources, and mixtures of both. Using estimates of in situ methane concentration from deep core samples and observations of in situ free gas occurrences, we conclude that the reservoir of in situ geologic methane within ice bonded permafrost is substantial and that this methane is presently migrating with ongoing atmospheric release. It is our assessment that the permafrost setting, and processes described are sensitive to future climate change as the permafrost warms.

Meandering rivers experience fluctuations in width whenever riverbanks migrate in different directions or at different rates, which can be observed after individual floods. However, meandering rivers maintain approximately constant widths over decadal timescales. This implies some timescale below which width fluctuates as banks migrate independently, and above which width is maintained by a bank-coupling process. This coupling is thought to occur either as point bar deposition events induce cutbank erosion (bar-push), or as cutbank erosion events induce point bar deposition (bank-pull). This coupling, however, has been challenging to observe in natural rivers due to limited event-scale field data. We present results from a 4.5-year campaign with 22 drone-based lidar surveys of a single point bar and cutbank (∼0.35 km² in area) on the White River near Worthington, Indiana, USA. The middle point bar experienced net erosion (5,400 m³), but net aggradation (17,100 m³) between 2019 and 2022 when including perennially submerged regions. This aggradation was less than the 35,700 m³ of cutbank erosion over the same period. Combined, we have observed widening (1.58 m/yr bend-averaged; 3.08 m/yr near apex) over the study period as point bar deposition has not kept up with cutbank erosion. Finally, we suggest that the difference between bar-push and bank-pull as width-maintenance mechanisms may not be resolvable by observing bend widening or narrowing alone without an advancement of current theory, such as determining a long-term equilibrium width and measuring deviations relative thereto.

The Tibetan Plateau (TP) serves not only as the “water tower” of Asia but also as an important source in the global atmospheric dust cycle. While our knowledge of modern dust activity and its impacts and interactions with climate change in the TP has greatly advanced in the past decades, the emission, transport, and deposition of dust on the geological time scale remains unclear. This study analyzed a 7.6-m thick sedimentary sequence consisting of loess and sand from the Yarlung Tsangpo River (YTR) valley in the southern TP. The sequence chronology was established using nineteen K-feldspar post-infrared infrared stimulated luminescence (pIRIR) ages, which ranged from 47.11 ± 1.95 to 116.65 ± 5.55 ka in a general stratigraphical order. The dust sedimentation rate and sorting coefficient of grain size were used to reflect dust activity and near-surface wind, respectively. The results indicated that dust activity in the southern TP is mainly regulated by the near-surface wind intensity and follows the variation pattern of precession, although the waxing and waning of mountain glaciers also affect the amplitude of dust activity. This pattern is not consistent with the Greenland dust record, which follows the variation pattern of obliquity. Therefore, dust accumulation in the southern TP is concluded to be primarily controlled by the South Asian winter monsoon (SAWM) forced by precession, whereas dust accumulation in Greenland is closely related to the intensity of the high-level westerlies forced by obliquity.

The present study focuses on heat transfer in ventilated caves for which the airflow is driven by the temperature contrast between the cave and the external atmosphere. We use a numerical model that couples the convective heat transfer due to the airflow in a single karst conduit with the conductive heat transfer in the rock mass. Assuming dry air and a simplified geometry, we investigate the propagation of thermal perturbations inside the karst massif. We perform a parametric study to identify general trends regarding the effect of the air flowrate and conduit size on the amplitude and spatial extent of thermal perturbations. Numerical results support the partition of a cave into three regions: (a) a short (few meters) diffusive region, where heat mainly propagates from the external atmosphere by conduction in the rock mass; (b) a convective region where heat is mainly transported by the air flow; (c) a deep karst region characterized by quasi-constant temperatures throughout the year. Numerical simulations show that the length of the convective region is approximately proportional to the amplitude of the flowrate annual fluctuations divided by the square root of the cave radius. This result is tested against field data from a mine tunnel and two caves. Our study provides first estimates to identify climate sensitive regions for speleothem science and/or ecosystemic studies.

Major earthquakes can cause extensive landsliding that poses a major threat to both property and human lives. In addition to co-seismically triggered ground failure, the earthquake-affected region remains vulnerable to landslides due to loosened and unstable materials and structures. Many researchers have studied landslide distributions and their controlling factors after earthquakes, but the function of ground motion is unclear. To investigate the connection in a strike-slip earthquake, we analyzed the 5 September 2022 Luding earthquake (M_w 6.6) in Sichuan Province, China. We interpreted remote-sensing images to obtain the landslide distribution before and after the earthquake, calculated surface deformation from D-InSAR data (pre- and post-earthquake), utilized a point-source model for the focal mechanism inversion, and then constructed a finite fault model for the rupture slip. There are clear differences in the landslide distributions on the two sides of the fault before and after the earthquake. The density of co-seismic landslides on the west side of the fault exceeded that on the east side. The patterns of surface deformation and ground motion indicated that the areas with larger deformation and motion were associated with more landslides. Furthermore, the landslide size decreased with distance from the fault. A new finding is that co-seismic landslides induced by strike-slip earthquakes result in high landslide concentration on both sides of the fault, while previous studies find that co-seismic landslides triggered by thrust earthquakes present a hanging wall concentrated distribution pattern. These findings contribute to a more comprehensive understanding of the connection between ground movement patterns and landslide distributions.