Termination (T) 5, ∼424 ka, involved the biggest deglaciation of land-ice mass during the Quaternary. Warming and ice-sheet retreat during T5 led to an exceptionally long period of interglacial ...warmth known as Marine Isotope Stage (MIS) 11, ∼424–395 ka. A detailed understanding of the history of continental ice-sheet decay during T5 is required to disentangle regional contributions of ice-sheet retreat to sea-level rise (that range between ∼1 and 13 m above present day) and to correct it for glacio-isostatic adjustments (GIA). Yet little is known about the timing and magnitude of retreat during this time of the volumetrically most important continental ice sheet in the Northern Hemisphere, the Laurentide Ice Sheet (LIS). Here we present new authigenic Fe-Mn oxyhydroxide-derived high-resolution records of Pb isotope data and associated rare earth element profiles for samples spanning T5 from Labrador Sea IODP Site U1302/3. These records feature astronomically-paced radiogenic Pb isotope excursions that track increases in chemical weathering of North American bedrock and freshwater routing to the Labrador Sea via Hudson Straits associated with LIS retreat. Our records show that LIS retreat during T5 began 429. 2 ± 7.9 ka (2σ) and likely occurred over a longer timescale (by ∼10 to 5 kyr) than that observed for T2 and T1. They also show that Hudson Bay Ice Saddle collapse (and therefore LIS break-up) occurred ∼419 ± 4.7 ka (2σ), around the same time as best estimates of southern Greenland deglaciation, but ∼12 kyr before LIS deglaciation and the sea-level high-stand associated with the latter half of MIS 11 likely occurred. Our findings therefore highlight that ice-mass loss on North America likely played an important role in the seemingly protracted nature of T5 sea-level rise. A comparison of the deglaciation histories of the LIS and the southern Greenland Ice Sheet during T5, T2 and T1 also demonstrates that the well-constrained history of regional ice-sheet retreat during T1 is not always applicable as a template for older late Pleistocene terminations in GIA modelling.
•We present a T5 record of the Pb isotope composition Labrador Sea seawater.•These data can be used to track Laurentide Ice Sheet (LIS) extent over Hudson Bay.•LIS retreat during T5 occurred over longer timescales than that for T2 and T1.•LIS deglaciation played important role in protracted nature of T5 sea-level rise.•Ice retreat during T1 may not be applicable template for older terminations in GIA modelling.
The Io plasma torus is thought to lie in Jupiter's centrifugal equator, a location that depends on Jupiter's rotation and magnetic field. Yet previous observations and predictions of the location of ...the Io plasma torus are inconsistent. Here we test the hypothesis that the Io plasma torus lies in the centrifugal equator by comparison of observations by Juno radio occultations to predictions derived from Juno‐era magnetic field models. These observations determine the locations of two torus components: The cold torus is centered near 5.3 Jovian radii (RJ), and the “torus beyond 5.5 RJ,” dominated by the warm torus, is centered near 5.9 RJ. The observations deviate by 1–2° from the planar centrifugal equator expected for a Voyager epoch dipolar magnetic field. In each observation, the locations of distinct torus regions differ by as much as 1° indicating significant radial structure. The root‐mean‐square error between observation and prediction is smaller for predictions from the JRM09 magnetic field model than for predictions from the VIP4 magnetic field model, confirming the JRM09 model is an improvement over the VIP4 model. Agreement between observations and predictions improves for the warm torus if the magnetic field contributions of a nominal magnetospheric current sheet model are included but worsens for the cold torus. Magnetic field conditions around 5.3 RJ are adequately represented by an internal field model without the current sheet. Conditions around 5.9 RJ require internal and external contributions. These results place constraints on properties of the magnetospheric current sheet during the Juno epoch.
Key Points
The JRM09 magnetic field model performs better at matching the radio occultation data than the VIP4 magnetic field model
The magnetic field induced by magnetospheric currents affects the Io plasma torus location
The Io plasma torus location may constrain properties of the magnetospheric current sheet
Chronic ulcers are wounds that are difficult to heal. We often encounter chronic ulcer cases that existing treatments do not cure. In this study, we found that allogeneic and autologous fibroblast ...sheets exhibited strong wound-healing effects in a mouse model.
Although cell sheets have therapeutic effects, they are difficult to handle, and tools are required for their transplantation. Therefore, we developed CY-1, a new substrate film, which we incubated and transplanted. Fibroblasts were incubated on CY-1 and then frozen in a 3D freezer. Fibroblast sheets were transplanted onto cutaneous defects on mice. New substrate films were collected from the transplanted sites after transplantation with the fibroblast sheets. The purpose of this study was to investigate the therapeutic efficacy of frozen–thawed allogeneic/xenogeneic fibroblast sheet transplantation cultured and frozen on CY-1 in mouse model of ulcers (Fig. 1).
To evaluate the therapeutic efficacy of the fibroblasts isolated from C3H mice incubated on CY-1, diabetic C57BL/6 mice were treated in one the following four groups: frozen–thawed allogenic fibroblast sheets cultured on CY-1, frozen–thawed allogenic fibroblast sheets cultured without CY-1, nonfrozen allogenic fibroblast sheets cultured on CY-1, and control. The wound-healing rate in the three fibroblast sheet transplantation groups was high compared with that of the control group from day 1 to 5, and no difference was found in the treatment outcome among the three fibroblast sheet transplantation groups (Fig. 2).
To evaluate the therapeutic efficacy of human fibroblasts incubated on CY-1, NOD/Scid mice were treated in one of the following two groups: frozen–thawed human fibroblast sheets cultured on CY-1 and control. Frozen–thawed human fibroblast sheets showed high therapeutic efficacy in terms of wound healing rate compared with the control group from day 1 to 11 (Fig. 3)
After transplanting human fibroblast cell sheets onto immunodeficient mice, the effects of cryopreservation were analyzed for human fibroblast cells with CY-1. Comparing the numbers against the 100% cell viability of human fibroblasts when seeded and incubated with CY-1 for 24 h, cell viability was approximately 30% just after thawing; cell viability was the same for human fibroblasts when incubated for 24 h after thawing as when not frozen.
Human allogenic fibroblast sheets incubated with CY-1 may have clinical application as a treatment for intractable ulcers.
Recent geologic and modeled evidence suggests that the grounding line of the Siple Coast of the West Antarctic Ice Sheet (WAIS) retreated hundreds of kilometers beyond its present position in the ...middle to late Holocene and readvanced within the past 1.7 ka. This grounding line reversal has been attributed to both changing rates of isostatic rebound and regional climate change. Here, we test these two hypotheses using a proxy-informed ensemble of ice sheet model simulations with varying ocean thermal forcing, global glacioisostatic adjustment (GIA) model simulations, and coupled ice sheet-GIA simulations that consider the interactions between these processes. Our results indicate that a warm to cold ocean cavity regime shift is the most likely cause of this grounding line reversal, but that GIA influences the rate of ice sheet response to oceanic changes. This implies that the grounding line here is sensitive to future changes in sub-ice shelf ocean circulation.
Subglacial drainage networks regulate the response of ice sheet flow to surface meltwater input to the subglacial environment. Simulating subglacial hydrology evolution is critical to projecting ice ...sheet sensitivity to climate, and contribution to sea‐level change. However, current numerical subglacial hydrology models are computationally expensive, and, consequently, evolving subglacial hydrology is neglected in large‐scale ice sheet simulations. We present a deep learning emulator of a state‐of‐the‐art subglacial hydrology model, trained at multiple Greenland glaciers. Our emulator performs strongly in both temporal (R2 > 0.99) and spatial (R2 > 0.95) generalization, offers high computational savings, and can be used to force numerical ice sheet models. This will enable century‐ and large‐scale ice sheet model simulations, including interactions between ice flow and increased meltwater input to the subglacial environment. Generally, our work demonstrates that machine learning can further improve ice sheet models, reduce computational bottlenecks, and exploit information from high‐fidelity models and novel observational platforms.
Plain Language Summary
Meltwater at the surface of ice sheets can drain to the subglacial environment, lubricate the bed, and influence ice sheet flow. Complex numerical subglacial hydrology models represent the subglacial drainage system, but are too computationally expensive to be included in large‐scale and long‐term ice sheet simulations. Consequently, model predictions of future ice sheet contribution to sea‐level rise ignore ice flow modulation by evolving subglacial hydrology. Here, we use deep learning to emulate a state‐of‐the‐art subglacial hydrology model. The emulator can directly force large‐scale ice sheet models to capture ice flow sensitivity to subglacial hydrology. The computational speed and accuracy of our emulator show the potential to use machine learning to efficiently incorporate previously neglected processes into ice sheet models.
Key Points
We develop a deep learning emulator to simulate evolving subglacial hydrology in response to meltwater input for ice sheet simulations
The emulator shows generalization capabilities, large computational savings, and can be used to force numerical ice sheet models
We demonstrate that machine learning has substantial potential in improving ice sheet models, through using information‐rich data sets
Ice-sheet simulations of Antarctica extending to the year 3000 are analysed to investigate the long-term impacts of 21st-century warming. Climate projections are used as forcing until 2100 and ...afterwards no climate trend is applied. Fourteen experiments are for the ‘unabated warming’ pathway, and three are for the ‘reduced emissions’ pathway. For the unabated warming path simulations, West Antarctica suffers a much more severe ice loss than East Antarctica. In these cases, the mass loss amounts to an ensemble average of ~3.5 m sea-level equivalent (SLE) by the year 3000 and ~5.3 m for the most sensitive experiment. Four phases of mass loss occur during the collapse of the West Antarctic ice sheet. For the reduced emissions pathway, the mean mass loss is ~0.24 m SLE. By demonstrating that the consequences of the 21st century unabated warming path forcing are large and long term, the results present a different perspective to ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). Extended ABUMIP (Antarctic BUttressing Model Intercomparison Project) simulations, assuming sudden and sustained ice-shelf collapse, with and without bedrock rebound, corroborate a negative feedback for ice loss found in previous studies, where bedrock rebound acts to slow the rate of ice loss.
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER ...catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active edge1T‐MoS2/edgeNi(OH)2 heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich edge1T‐MoS2/edgeNi(OH)2 sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm−2, respectively, and has a low Tafel slope of 30 mV dec−1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm−2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions.
Edge1T‐MoS2/edgeNi(OH)2 heterostructures are highly active toward alkaline hydrogen evolution reaction (HER). The prepared 1T–MoS2 quantum sheet/Ni(OH)2 catalyst with rich edge1T‐MoS2/edgeNi(OH)2 sites efficiently dissociates H2O to produce H2 in alkaline media in a bi‐functional manner, delivering excellent alkaline HER activity and stability surpassing that of Pt/C at high HER current densities (up to 500 mA cm−2).
Generalizations of the class of quasi‐1‐D solutions of the 2‐D Grad‐Shafranov equation, first considered by Schindler in 1972, are investigated. It is shown that the effect of the dipole field, ...treated as a perturbation, can be included into the original 1972 class solution by modification of the boundary conditions. Some of the solutions imply the formation of singularly thin current sheets. Equilibrium solutions for such sheets resolving their singular current structure on the scales comparable to the thermal ion gyroradius can be obtained assuming anisotropic and nongyrotropic plasma distributions. It is shown that one class of such equilibria with the dipole‐like boundary perturbation describes bifurcation of the near‐Earth current sheet. Another class of weakly anisotropic equilibria with thin current sheets embedded into a thicker plasma sheet helps explain the formation of thin current sheets in a relatively distant tail, where such sheets can provide ion Landau dissipation for spontaneous magnetic reconnection. The free energy for spontaneous reconnection can be provided due to accumulation of the magnetic flux at the tailward end of the closed field line region. The corresponding hump in the normal magnetic field profile Bz(x,z = 0) creates a nonzero gradient along the tail. The resulting gradient of the equatorial magnetic field pressure is shown to be balanced by the pressure gradient and the magnetic tension force due to the higher‐order correction of the latter in the asymptotic expansion of the tail equilibrium in the ratio of the characteristic tail current sheet variations across and along the tail.
Key Points
Dipole field effects reduce to boundary perturbations and involve thin current sheets
Embedded sheets explain thin current sheet formation far from the dipole region
Force balance in equilibria with accumulated magnetic flux is explained
Sea-level rise may accelerate significantly if marine ice sheets become unstable. If such instability occurs, there would be considerable uncertainty in future sea-level rise projections due to ...imperfectly modeled ice sheet processes and unpredictable climate variability. In this study, we use mathematical and computational approaches to identify the ice sheet processes that drive uncertainty in sea-level projections. Using stochastic perturbation theory from statistical physics as a tool, we show mathematically that the marine ice sheet instability greatly amplifies and skews uncertainty in sea-level projections with worst-case scenarios of rapid sea-level rise being more likely than best-case scenarios of slower sea-level rise. We also perform large ensemble simulations with a state-of-the-art ice sheet model of Thwaites Glacier, a marine-terminating glacier in West Antarctica that is thought to be unstable. These ensemble simulations indicate that the uncertainty solely related to internal climate variability can be a large fraction of the total ice loss expected from Thwaites Glacier. We conclude that internal climate variability alone can be responsible for significant uncertainty in projections of sea-level rise and that large ensembles are a necessary tool for quantifying the upper bounds of this uncertainty.
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