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The mass budget of southern Patagonian glaciers is characterized by an extreme amount of surface ablation. To understand the processes controlling surface mass balance, we analyzed in situ data including meteorological variables and ablation stakes for the 25 years between 1996 and 2020 near the terminus of Glaciar Perito Moreno in southern Patagonia in South America. The mean annual temperature has increased over the study period at a rate of 0.2°C decade−1. An energy-balance model was applied to calculate a point surface mass balance, based on meteorological records. The average point surface mass balance is estimated to be -16.3 m water equivalent (w.e.) yr-1 between 1996 and 2020, decreasing at a rate in the range from-0.4 to-0.9 m w.e. yr-1 decade-1. The greatest contribution to the surface en-ergy balance was due to the sensible heat flux, and its variation drove the surface mass balance variation. The meteo-rological and surface mass balance records were compared with the Southern Annular Mode and El Niño–Southern Oscillation, which change the atmospheric circulation over southern Patagonia and influence surface mass balance near the terminus of the glacier. Our long-term dataset investigates the detailed meteorological conditions and surface mass balance and their connection with the large-scale climate variability over the last 25 years, reported for the first time in Patagonia.

In order to construct reliable deposited-aerosol database on the Anthropocene (from 1850 to 2020), we obtained a 250-meter-long ice core from the Southeastern Greenland Dome on May and June 2021, where is one of the highest accumulation domes in Greenland. The age of the ice core at a depth of 250 m was roughly estimated to be AD 1827 based on the timescale from a previously analyzed shallower ice core. The age of the sampled ice core satisfied the prerequisite conditions for constructing aerosol deposition database for Anthropocene. In addition, surface elevation, borehole temperatures, and internal stratigraphy of the ice sheet were performed, and meteorological and snow-pit observations were also conducted. Furthermore, we sampled aerosol and snow from the ice sheet for chemical and physical analyses.

The complex dynamics of calving glaciers is a major uncertainty in projecting global glacial mass loss. We present frontal ablation and ice mass change for the 38 major calving glaciers in the Patagonian icefields based on remote-sensing observations of ice-front positions, surface speeds and elevation changes. The frontal ablation from 2000 to 2019 was −24.1 ± 1.7 Gt a−1, which represents 34 ± 6% of the total ablation of the icefields. The fraction of frontal ablation was close to half in the southern icefield and about one fifth in the northern icefield. The rate of the mass loss from the icefields during the period of study was 15.2 ± 3.5 Gt a−1, which is generally explained by surface mass balance but was accelerated as a result of increasing frontal ablation. The frontal ablation and mass change values suggest surface mass balance to be −1.5 ± 0.9 Gt a−1 for the northern icefield and +11.5 ± 2.7 Gt a−1 for the southern icefield during this period. Our study demonstrates that a strong increase in frontal ablation at several glaciers drives the mass loss in the southern icefield, whereas increasingly negative surface mass balance drives the mass loss in the northern icefield.

The complex dynamics of calving glaciers is a major uncertainty in projecting global glacial mass loss. We present frontal ablation and ice mass change for the 38 major calving glaciers in the Patagonian icefields based on remote-sensing observations of ice-front positions, surface speeds and elevation changes. The frontal ablation from 2000 to 2019 was −24.1 ± 1.7 Gt a−1, which represents 34 ± 6% of the total ablation of the icefields. The fraction of frontal ablation was close to half in the southern icefield and about one fifth in the northern icefield. The rate of the mass loss from the icefields during the period of study was 15.2 ± 3.5 Gt a−1, which is generally explained by surface mass balance but was accelerated as a result of increasing frontal ablation. The frontal ablation and mass change values suggest surface mass balance to be −1.5 ± 0.9 Gt a−1 for the northern icefield and +11.5 ± 2.7 Gt a−1 for the southern icefield during this period. Our study demonstrates that a strong increase in frontal ablation at several glaciers drives the mass loss in the southern icefield, whereas increasingly negative surface mass balance drives the mass loss in the northern icefield.

Water temperature in glacial lakes affects underwater melting and calving of glaciers terminating in lakes. Despite its importance, seasonal lake temperature variations are poorly understood because taking long-term measurements near the front of calving glaciers is challenging. To investigate the thermal structure and its seasonal variations, we performed year-around temperature and current measurement at depths of 58-392 m in Lago Grey, a 410-m-deep glacial lake in Patagonia. The measurement revealed critical impacts of subglacial discharge on the lake thermal condition. Water below a depth of -100 m showed the coldest temperature in mid-summer, under the influence of glacial discharge, whereas temperature in the upper layer followed a seasonal variation of air temperature. The boundary of the lower and upper layers was controlled by the depth of a sill which blocks outflow of dense and cold glacial meltwater. Our data implies that subglacial discharge and bathymetry dictate mass loss and the retreat of lake-terminating glaciers. The cold lakewater hinders underwater melting and facilitates formation of a floating terminus.

In order to construct reliable deposited-aerosol database on the Anthropocene (from 1850 to 2020), we obtained a 250-meter-long ice core from the Southeastern Greenland Dome on May and June 2021, where is one of the highest accumulation domes in Greenland. The age of the ice core at a depth of 250 m was roughly estimated to be AD 1827 based on the timescale from a previously analyzed shallower ice core. The age of the sampled ice core satisfied the prerequisite conditions for constructing aerosol deposition database for Anthropocene. In addition, surface elevation, borehole temperatures, and internal stratigraphy of the ice sheet were performed, and meteorological and snow-pit observations were also conducted. Furthermore, we sampled aerosol and snow from the ice sheet for chemical and physical analyses.

We recorded the ice motion and icequakes on the floating part of Langhovde Glacier in East Antarctica to better understand the dynamic behavior of ice shelves and floating tongues. Diurnal and semi-diurnal variations in ice motion and seismicity were simultaneously observed at all four global navigation satellite system and three seismic stations over 2 weeks. The short-term along-flow ice motion is explained by the elastic response of the glacier to ocean tide-induced hydrostatic stress variations, which decayed at a rate of 0.8 km(-1) toward the grounding line. We observed a large number of icequakes during mid-rising and high tides that covered a broad frequency range and formed two major groups of events centered at 10 and 120 Hz, respectively. The hourly occurrence rates were similar to 500 events h(-1), with the observed seismicity consistent with fracture due to floating tongue bending. We also observed minor secondary peaks at high ice speeds, which could reflect surface cracking due to stretching or basal friction. Our observation demonstrates that tidal-modulation was the main factor to fracture the floating tongue of Langhovde Glacier.

We use the full-Stokes model Elmer/Ice to investigate the present dynamics of Bowdoin Glacier, a marine-terminating outlet glacier in northwestern Greenland. Short-term speed variations of the glacier were observed, correlating with air temperature and precipitation, and with the semi-diurnal ocean tides. We use a control inverse method to determine the distribution of basal friction. This reveals that most of the glacier area is characterized by near-plug-flow conditions, while some sticky spots are also identified. We then conduct experiments to test the sensitivity of the glacier flow to basal lubrication and tidal forcing at the calving front. Reduction of the basal drag by 10–40% produces speed-ups that agree approximately with the observed range of speed-ups that result from warm weather and precipitation events. In agreement with the observations, tidal forcing and surface speed near the calving front are found to be in anti-phase (high tide corresponds to low speed, and vice versa). However, the amplitude of the semi-diurnal variability is underpredicted by a factor ~ 3, which is likely related to either inaccuracies in the surface and bedrock topographies or mechanical weakening due to crevassing.

To study subglacial hydrological condition and its influence on the glacier dynamics, we drilled Johnsons Glacier on Livingston Island in the Antarctic Peninsula region. Subglacial water pressure was recorded in boreholes at two locations over 2 years, accompanied by high-frequency ice-speed measurements during two summer melt seasons. Water pressure showed two different regimes, namely high frequency and large amplitude variations during the melt season (January-April) and small fluctuations near the overburden pressure the rest of the year. Speed-up events were observed several times in each summer measurement period. Ice motion during these events substantially contributed to total glacier motion, for example, fast ice flow over 1 week accounted for similar to 70% of the total displacement over a 25-day long measurement period. We did not find a clear relationship between subglacial water pressure and ice speed. This was probably because subglacial hydraulic conditions were spatially inhomogeneous and thus our borehole data did not always represent a large-scale subglacial condition. Ice temperature measurements in the boreholes confirmed the existence of a cold ice layer near the glacier surface. Our data provide a basis to better understand the dynamic and hydrological conditions of relatively unstudied glaciers in the Antarctic Peninsula region.

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 100m 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. Plain Language Summary 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.

Measuring glacier calving magnitude, frequency and location in high temporal resolution is necessary to understand mass loss mechanisms of ocean-terminating glaciers. We utilized calving-generated tsunami signals recorded with a pressure sensor for estimating the calving flux of Bowdoin Glacier in northwestern Greenland. We find a relationship between calving ice volume and wave amplitude. This relationship was used to compute calving flux variation. The calving flux showed large spatial and temporal fluctuations in July 2015 and in July 2016, with a mean flux of 2.3 ± 0.15 × 105 m3 d−1. Calving flux was greater during periods of fast ice flow, high air temperature, and at low/falling tide, indicating the importance of increased longitudinal strain due to glacier acceleration and/or submarine melting at the calving front. Long-term measurements with the method introduced here are promising for understanding the complex interplay of ice dynamics, melting and calving at glacier fronts.

Measuring glacier calving magnitude, frequency and location in high temporal resolution is necessary to understand mass loss mechanisms of ocean-terminating glaciers. We utilized calving-generated tsunami signals recorded with a pressure sensor for estimating the calving flux of Bowdoin Glacier in northwestern Greenland. We find a relationship between calving ice volume and wave amplitude. This relationship was used to compute calving flux variation. The calving flux showed large spatial and temporal fluctuations in July 2015 and in July 2016, with a mean flux of 2.3 ± 0.15 × 105 m3 d−1. Calving flux was greater during periods of fast ice flow, high air temperature, and at low/falling tide, indicating the importance of increased longitudinal strain due to glacier acceleration and/or submarine melting at the calving front. Long-term measurements with the method introduced here are promising for understanding the complex interplay of ice dynamics, melting and calving at glacier fronts.

Calving plays a key role in the recent rapid retreat of glaciers around the world. However, many processes related to calving are poorly understood since direct observations are scarce and challenging to obtain. When calving occurs at a glacier front, surface-water waves arise over the ocean or a lake in front of glaciers. To study calving processes from these surface waves, we performed field observations at Glaciar Perito Moreno, Patagonia. We synchronized time-lapse photography and surface waves record to confirm that glacier calving produces distinct waves compared with local noise. A total of 1074 calving events were observed over the course of 39 d. During austral summer, calving occurred twice more frequently than in spring. The cumulative distribution of calving-interevent time interval followed exponential model, implying random occurrence of events in time. We further investigated wave properties and found that source-to-sensor distance can be estimated from wave dispersion within ∼20% error. We also found that waves produced by different calving types showed similar spectra in the same frequency range between 0.05–0.2 Hz, and that the amplitude of surface waves increased with the size of calving. This study demonstrates the potential of surface-wave monitoring for understanding calving processes.

Calving plays a key role in the recent rapid retreat of glaciers around the world. However, many processes related to calving are poorly understood since direct observations are scarce and challenging to obtain. When calving occurs at a glacier front, surface-water waves arise over the ocean or a lake in front of glaciers. To study calving processes from these surface waves, we performed field observations at Glaciar Perito Moreno, Patagonia. We synchronized time-lapse photography and surface waves record to confirm that glacier calving produces distinct waves compared with local noise. A total of 1074 calving events were observed over the course of 39 d. During austral summer, calving occurred twice more frequently than in spring. The cumulative distribution of calving-interevent time interval followed exponential model, implying random occurrence of events in time. We further investigated wave properties and found that source-to-sensor distance can be estimated from wave dispersion within ∼20% error. We also found that waves produced by different calving types showed similar spectra in the same frequency range between 0.05–0.2 Hz, and that the amplitude of surface waves increased with the size of calving. This study demonstrates the potential of surface-wave monitoring for understanding calving processes.

The front position of calving glaciers is controlled by ice speed and frontal ablation which consists of the two processes of calving and subaqueous melting. However, the relative importance of these processes in frontal variation is difficult to assess and poorly understood, particularly for freshwater calving glaciers. To better understand the mechanism of seasonal variations involved in the ice front variations of freshwater calving glaciers, we measured front position, ice surface speed, air temperature, and proglacial lakewater temperature of Glaciar Perito Moreno in Patagonia. No substantial fluctuations in front position and ice speed occurred during the 15-year period studied (1999-2013), despite a warming trend in air temperature (0.059 degrees C a(-1)). Seasonal variations were observed both in the ice-front position (+/- 50 m) and ice speed (+/- 15%). The frontal ablation rate, computed from the frontal displacement rate and the ice speed, varied in a seasonal manner with an amplitude approximately five times greater than that in the ice speed. The frontal ablation correlated well with seasonal lakewater temperature variations (r = 0.96) rather than with air temperature (r = 0.86). Our findings indicate that the seasonal ice front variations of Glaciar Perito Moreno are primarily due to frontal ablation, which is controlled through subaqueous melting by the thermal conditions of the lake.

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 similar to 180 m, forming a relatively warm isothermal layer (mean temperature of similar to 5-6 degrees C at Perito Moreno, similar to 3-4 degrees C at Upsala, and similar to 6-7 degrees 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.

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 250m 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.

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 similar to 180 m, forming a relatively warm isothermal layer (mean temperature of similar to 5-6 degrees C at Perito Moreno, similar to 3-4 degrees C at Upsala, and similar to 6-7 degrees 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.