Meltwater Pulse 1A sea-level-rise patterns explained by global cascade of ice loss
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Winter subglacial meltwater detected in a Greenland fjord
The interaction between glacier fronts and ocean waters is one of the key uncertainties for projecting future ice mass loss. Direct observations at glacier fronts are sparse, but studies indicate that the magnitude and timing of freshwater fluxes are crucial in determining fjord circulation, ice frontal melt and ecosystem habitability. In particular, wintertime dynamics are severely understudied due to inaccessible conditions, leading to a bias towards summer observations. Here we present in situ observations of temperature and salinity acquired in late winter in Greenland at the front of a marine-terminating glacier and in surrounding fjords. Our observations indicate the existence of an anomalously fresh pool of water by the glacier front, suggesting that meltwater generated at the bed of the glacier discharges during winter. The results suggest that warm Atlantic water and nutrients are entrained at the glacier front, leading to enhanced frontal melt and increased nutrient levels. Our findings have implications for understanding the heat exchange between glacier fronts and ocean waters, glacier frontal melt rates, ocean mixing and currents, and biological productivity.
Methane emissions from thermokarst lakes must emphasize the ice-melting impact on the Tibetan Plateau
Thermokarst lakes, serving as significant sources of methane (CH4), play a crucial role in affecting the feedback of permafrost carbon cycle to global warming. However, accurately assessing CH4 emissions from these lakes remains challenging due to limited observations during lake ice melting periods. In this study, by integrating field surveys with machine learning modeling, we offer a comprehensive assessment of present and future CH4 emissions from thermokarst lakes on the Tibetan Plateau. Our results reveal that the previously underestimated CH4 release from lake ice bubble and water storage during ice melting periods is 11.2 ± 1.6 Gg C of CH4, accounting for 17 ± 4% of the annual total release from lakes. Despite thermokarst lakes cover only 0.2% of the permafrost area, they annually emit 65.5 ± 10.0 Gg C of CH4, which offsets 6.4% of the net carbon sink in alpine grasslands on the plateau. Considering the loss of lake ice, the expansion of thermokarst lakes is projected to lead to 1.1–1.2 folds increase in CH4 emissions by 2100. Our study allows foreseeing future CH4 emissions from the rapid expanding thermokarst lakes and sheds new lights on processes controlling the carbon-climate feedback in alpine permafrost ecosystems.
Advancements in ultrafast photonics: confluence of nonlinear optics and intelligent strategies
Automatic mode-locking techniques, the integration of intelligent technologies with nonlinear optics offers the promise of on-demand intelligent control, potentially overcoming the inherent limitations of traditional ultrafast pulse generation that have predominantly suffered from the instability and suboptimality of open-loop manual tuning. The advancements in intelligent algorithm-driven automatic mode-locking techniques primarily are explored in this review, which also revisits the fundamental principles of nonlinear optical absorption, and examines the evolution and categorization of conventional mode-locking techniques. The convergence of ultrafast pulse nonlinear interactions with intelligent technologies has intricately expanded the scope of ultrafast photonics, unveiling considerable potential for innovation and catalyzing new waves of research breakthroughs in ultrafast photonics and nonlinear optics characters.
Active ice sheet conservation cannot stop the retreat of Sermeq Kujalleq glacier, Greenland
Active conservation of an ice sheet seeks to reduce ice sheet mass loss and sea level rise. Here we explore the response of Sermeq Kujalleq in Greenland to limiting warm water inflow to the fjord it terminates by raising the sill by an artificial barrier at its mouth. We asynchronously couple an ice sheet model with a fjord model, and simulate glacier evolution with varying climate scenarios from the year 2020 to 2100. The tallest barrier cools the fjord water and reduces melt at the ice front. But this has minor impacts on glacier retreat under SSP5-8.5 and SSP2-4.5. Cooling the atmospheric forcing to 1990s levels reduces glacier retreat, but even reducing water temperatures with a barrier cannot stabilize the glacier. The glacier seems to be in an unstoppable phase of marine ice sheet instability on a rapidly deepening retrograde sloping bed and in water much deeper than in 2000s.
Rare ice-base temperature measurements in Antarctica reveal a cold base in contrast with predictions
The Antarctic bed demonstrates complex behaviour comprising alternating warm- and cold-based areas. However, the distribution of warm- and cold-based areas, basal melting rates, and the structure and age of the basal ice are not yet fully known. In the 2023–2024 season, we drilled an access borehole through 541 m thick ice at Princess Elizabeth Land, 28 km south of the coast. Temperature measurements at the bottom of the borehole revealed a cold underlying base despite a warm-based interface being predicted in advance as the most likely estimate. Our results imply that the Antarctic base can be locally colder than currently assumed, and that thermal models, especially basal boundary conditions, should be carefully specified and provided with the confirmed input data.
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