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Underwater ice geometry at the front of calving glaciers provides crucial information for calving and underwater melting. In this study, we present ice geometry captured by operating a side‐scanning sonar near the front of Glaciar Grey, a freshwater calving glacier in Patagonia. The observations revealed ice projecting into the lake with a substantially different structure from that of known tidewater glaciers. Terrace‐like ice structures were found at several tens of meters below the water surface and extended up to 100 m from the aerial ice front. The structure depicted by the sonar was confirmed when the ice front was exposed by flotation during a major calving event. We infer that buoyant force acting on the submerged ice terrace acted as a driver of the calving event. Our study demonstrates the importance of the underwater ice geometry, which affects sizable calving at the front of freshwater calving glaciers. Glaciers terminating in lakes and the ocean are in general retreating more rapidly than glaciers on land. This is because such glaciers lose ice by discharging icebergs and melting in water. The shape of the submerged part of the ice front provides important information for understanding iceberg production and melting, but measurements near the glacier front are difficult to obtain. In this study, we used a side‐scanning sonar to visualize underwater ice of a lake terminating glacier in Patagonia. The observations revealed ice jutting into the lake, forming terrace‐like structures several tens of meters below the water surface. The structure was significantly different from that of ocean terminating glaciers. The observation was confirmed when the ice front was detached from the glacier and exposed by flotation. Our study demonstrates that buoyant force acting on the ice terrace plays a key role in the production of large icebergs at the front of freshwater calving glaciers. Subaqueous calving front of a Patagonian glacier was captured by a side‐scanning sonarGlacier front forms a terrace‐like structure in the lakeBuoyant force acting on the underwater ice promotes large‐scale calving

Arctic warming has accelerated surface melting even in the highland areas of the Greenland ice sheet (GrIS). Understanding the relationship between climate and surface melting is essential for improving the estimates of ice‐sheet mass loss due to warming. Here we analyze a 250 m‐long ice core from the southeastern dome of GrIS (SE‐Dome site; 67°19′17″ N, 36°47′03″ W, 3,161 m a.s.l.), where the annual mean temperature is −20.9°C and the accumulation rate is high and there is a large discrepancy among climate models regarding snow accumulation estimates. A time scale was established for 1799–2020 with a half‐year uncertainty using annual counting of H2O2concentration and five time horizons determined by electrical conductivity, melt events, and tritium concentration. The annual accumulation rate from the ice core shows no significant trend over 221 years and has an average of 1.04 ± 0.20 m w.e. year−1. In contrast, the frequency and thickness of refrozen melt layer (ML) have increased over 221 years, and are synchronized with temperature changes in the Arctic. The thickness of MLs correlates positively with the time‐integrated summer temperature anomaly using a reanalysis of air temperature. The in‐situ accumulation records in the southeastern GrIS provide an important basis for correcting reanalysis data such as ERA5, which in turn are valuable for improving regional climate models. In recent years, Arctic temperatures have been increasing faster than global temperatures. In the inland Greenland ice sheet (GrIS), the surface snow melts on warm days, then the meltwater percolates in the snowpack and refreezes into melt layers (MLs). Here we describe an ice core, collected from the southeastern GrIS, which contains records of precipitation and MLs from 1799 to 2020. We then compare these results with the climatic data. The annual precipitation rate obtained from the ice core shows neither a decrease nor an increase over 221 years, suggesting no significant trend in the southeastern region. On the other hand, with Arctic warming, the ML thickness per year has increased through the 19th–21st centuries. In addition, there is a positive correlation between ML thickness and summer temperature. We conclude that the annual precipitation rate in southeastern GrIS is constant regardless of Arctic warming and the ice core is favorable for reconstructing environmental records from the pre‐industrial era to the present. From an ice core in the southeastern Greenland ice sheet, we establish a time scale spanning 1799–2020 with a half‐year uncertaintyOver 221 years, the annual accumulation rate shows no significant trend, while the melt layer thickness has increased with Arctic warmingThe in‐situ accumulation records provide an important basis for correcting reanalysis data, which in turn are valuable for improving models From an ice core in the southeastern Greenland ice sheet, we establish a time scale spanning 1799–2020 with a half‐year uncertainty Over 221 years, the annual accumulation rate shows no significant trend, while the melt layer thickness has increased with Arctic warming The in‐situ accumulation records provide an important basis for correcting reanalysis data, which in turn are valuable for improving models

Calving glaciers are rapidly retreating in many regions under the influence of ice‐water interactions at the glacier front. In contrast to the numerous researches conducted on fjords in front of tidewater glaciers, very few studies have been reported on lakes in which freshwater calving glaciers terminate. To better understand ice‐water interactions at the front of freshwater calving glaciers, we measured lakewater temperature, turbidity, and bathymetry near Glaciar Perito Moreno, Upsala, and Viedma, large calving glaciers of the Southern Patagonia Icefield. The thermal structures of these lakes were significantly different from those reported in glacial fjords. There was no indication of upwelling subglacial meltwater; instead, turbid and cold glacial water discharge filled the region near the lake bottom. This was because water density was controlled by suspended sediment concentrations rather than by water temperature. Near‐surface wind‐driven circulation reaches a depth of ~180 m, forming a relatively warm isothermal layer (mean temperature of ~5–6°C at Perito Moreno, ~3–4°C at Upsala, and ~6–7°C at Viedma), which should convey heat energy to the ice‐water interface. However, the deeper part of the glacier front is in contact with stratified cold water, implying a limited amount of melting there. In the lake in front of Glaciar Viedma, the region deeper than 120 m was filled entirely with turbid and very cold water at pressure melting temperature. Our results revealed a previously unexplored thermal structure of proglacial lakes in Patagonia, suggesting its importance in the subaqueous melting of freshwater calving glaciers. Lakewater temperature, turbidity, and bathymetry measured near large calving glaciers of the Southern Patagonia IcefieldThermal structure of the lakes characterized by wind‐mixed warm water near the surface and cold/turbid glacial discharge near the bottomCold water at pressure melting point fills lower half of the lake of Glaciar Viedma, affecting subaqueous melting of the ice front

Glacier microseismicity is a promising tool to study glacier dynamics. However, physical processes connecting seismic signals and ice dynamics are not clearly understood at present. Particularly, the relationship between tide‐modulated seismicity and dynamics of calving glaciers remains elusive. Here we analyze records from an on‐ice seismometer placed 250 m from the calving front of Bowdoin Glacier, Greenland. Using high‐frequency glacier flow speed measurements, we show that the microseismic activity is related to strain rate variations. The seismic activity correlates with longitudinal stretching measured at the glacier surface. Both higher melt rates and falling tides accelerate glacier motion and increase longitudinal stretching. Long‐term microseismic monitoring could therefore provide insights on how a calving glacier's force balance and flow regime react to changes at the ice‐ocean interface. Near‐source records of seismicity at a calving frontFirst evidence of clear tidal modulation of cryoseismic activity in GreenlandVariation in longitudinal extensional strain rates drives microseismicity