Global ice volume peaked between ~26,500 and 19,000 years ago and resulted in the Laurentide, Innuitian and Greenland ice sheets coalescing in Baffin Bay, a semi-enclosed basin between Greenland and Canada. However, the configuration of their marine terminating margins, which help establish the boundary conditions and sensitivity to processes that govern ice-sheet retreat, remains unclear. Here we compile bathymetric data and report a geomorphic study of the Baffin Bay continental slope. We provide evidence for slope-grounded ice during the last glacial interval and trace its maximum depth imprint around most of Baffin Bay. We interpret ice-contact features to have resulted from a basin-spanning ice shelf that was ~1,400–2,100 m thick, once corrected for relative sea level. The extensive ice shelf (150,000 km2), supported by the basin geometry, buttressed, mechanically coupled, and promoted thickening of the adjacent ice sheets. Informed by sediment cores, we infer that ice-shelf collapse triggered rapid ice-sheet retreat, linking abrupt Northern Hemisphere ice-sheet instability to embayment-scale ice-shelf dynamics. The Baffin Bay Ice Shelf shows that ice-shelf loss can rapidly reorganize marine ice sheets, an analogue for how weakening buttresses may accelerate future Antarctica ice-stream retreat. An enormous ice shelf spanned Baffin Bay during the last glacial period, and its rapid retreat during the last deglaciation probably destabilized the surrounding ice sheets, according to an analysis of bathymetric data
The Antarctic Ice Sheet is expected to be the largest contributor to sea-level rise over the coming centuries. Previous equilibrium ice-sheet simulations have suggested that this is due to crossing a bifurcation point associated with marine ice-sheet instability. Here we investigate whether sectors vulnerable to this instability can undergo rate-induced tipping, whereby rapid forcing and slow bedrock uplift trigger self-sustained retreat before the bifurcation point is reached. We test this with an ice-sheet model coupled to a glacial isostatic adjustment model, sampling the uncertainty in mantle viscosity. We find that slow bedrock adjustment weakens the stabilizing effect of glacial isostatic adjustment, allowing grounding lines to reach retrograde bed slopes more readily and triggering self-sustained retreat below the bifurcation threshold. Although the West Antarctic Ice Sheet is subject to a bifurcation, it is unlikely to experience rate-induced tipping because of the low mantle viscosity beneath the region. In contrast, the Recovery and Aurora subglacial basins are likely to undergo such a transition even under warming rates lower than those observed today. Depending on mantle viscosity, this mechanism can reduce the critical global mean temperature anomaly by up to 0.5 K, with important implications for the long-term evolution of the Earth system. Delayed bedrock uplift can allow rapid warming to trigger Antarctic Ice Sheet retreat before classical instability thresholds are reached, lowering critical warming thresholds by up to 0.5 K in East Antarctica, according to coupled model simulations.
Uncritical extrapolation of soil erosion models developed in the Global North to Global South settings for which they were not designed reflects and perpetuates neocolonial biases in geoscience. To build a more accurate and equitable understanding of land degradation, we must rethink erosion research.
Dryland ecosystems store large amounts of both soil organic and inorganic carbon, yet the responses of soil inorganic carbon to global environmental change remain largely overlooked despite the potential vulnerability of this carbon pool. Here we aim to determine how soil inorganic and organic carbon respond to multiple global change drivers (warming, reactive nitrogen input and altered precipitation) using an 8-year field manipulation experiment in a semi-arid grassland and a meta-analysis based on 44 observations. We found that altered precipitation has no effect on soil inorganic carbon, but warming and nitrogen input interactively affect it. Specifically, nitrogen input alone does not affect soil inorganic carbon, but it increases soil inorganic carbon loss (~9.1%) when combined with climate warming. This inorganic carbon loss co-occurs with enhanced microbial nitrogen mineralization and nitrification, suggesting that enhancement of proton production due to nitrification controls soil inorganic carbon dissolution and persistence. Furthermore, both the field study and meta-analysis show that nitrogen input and/or warming induce contrasting changes in soil inorganic and organic carbon, suggesting a trade-off between soil inorganic and organic carbon under these two major global change drivers. These results highlight the need to account for the vulnerability of soil inorganic carbon when predicting dryland carbon dynamics under future climate change scenarios. Global environmental changes can induce contrasting responses of soil organic and inorganic carbon, according to an 8-year field experiment in a semi-arid grassland and a meta-analysis.
Arctic sea ice decline has been observed across all seasons and is projected to continue in the future. Relative to historical observations, climate models show their largest biases and uncertainties during winter, when ice cover strongly regulates air–sea heat exchange, ocean mixing and atmospheric circulation. Palaeoclimate records offer opportunities to evaluate model performance beyond the historical period, but applications have remained largely qualitative. Here we compile an Arctic-wide database of mid-Holocene (5–7 thousand years ago) biomarkers to assess sea ice simulations of this past warm period. Using a recently developed proxy system model, we present a Bayesian palaeoclimate model weighting scheme that refines the multi-model mean winter sea ice extent through fully quantitative proxy-model comparisons, accounting for model interdependence and non-stationary proxy seasonality. We demonstrate that, by adjusting the contribution of each model to the ensemble mean based on proxy evidence, model weights can eliminate biases and reduce uncertainties by 85%, to the level of interannual variability. Weighted projections using the same climate models indicate that future winter sea ice extent may be nearly 1 million km2 lower than prior estimates across forthcoming decades and possible emissions scenarios, with broad implications for Arctic ecosystems, mid-latitude weather, and cryosphere stability. Forecasts of future Arctic Ocean sea ice loss can be substantially improved using Holocene proxy records by applying a model weighting approach.
