Floating Glacier Tongue Research Articles

An Improved and Observationally‐Constrained Melt Rate Parameterization for Vertical Ice Fronts of Marine Terminating Glaciers

AbstractSubmarine melting at Greenland's marine terminating glaciers is a crucial, yet poorly constrained process in the coupled ice‐ocean system. Application of Antarctic melt rate representations, derived for floating glacier tongues, to non‐floating marine terminating glaciers commonly found in Greenland, results in a dramatic underestimation of submarine melting. Here, we revisit the physical theory underlying melt rate parameterizations and leverage recently published observational data to derive a novel melt rate parameterization. This is the first parameterization that (a) consistently comprises both convective‐ and shear‐dominated melt regimes, (b) includes coefficients quantitatively constrained using observational data, and (c) is applicable to any vertical glacier front. We show that, compared to the current state‐of‐the‐art approach, the scheme provides an improved fit to observed melt rates on the scale of the terminating front, offering an opportunity to incorporate this critical missing forcing into ocean circulation models.

Bathymetry constrains ocean heat supply to Greenland’s largest glacier tongue

Mass loss from the Greenland ice sheet has increased over the past two decades, currently accounting for 25% of global sea-level rise. This is due to increased surface melt driven by atmospheric warming and the retreat and acceleration of marine-terminating glaciers forced by oceanic heat transport. We use ship-based profiles, bathymetric data and moored time series from 2016 to 2017 of temperature, salinity and water velocity collected in front of the floating tongue of the 79 North Glacier in Northeast Greenland. These observations indicate that a year-round bottom-intensified inflow of warm Atlantic Water through a narrow channel is constrained by a sill. The associated heat transport leads to a mean melt rate of 10.4 ± 3.1 m yr–1 on the bottom of the floating glacier tongue. The interface height between warm Atlantic Water and colder overlying water above the sill controls the ocean heat transport’s temporal variability. Historical hydrographic data show that the interface height has risen over the past two decades, implying an increase in the basal melt rate. Additional temperature profiles at the neighbouring Zachariae Isstrom suggest that ocean heat transport here is similarly controlled by a near-glacier sill. We conclude that near-glacier, sill-controlled ocean heat transport plays a crucial role for glacier stability. Ocean heat transport underneath the floating tongue of 79 North Glacier, Greenland, is controlled by a sill in the inflow channel, according to ship-based and mooring data as well as bathymetric data.

Tide-modulated ice motion and seismicity of a floating glacier tongue in East Antarctica

ABSTRACTWe 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 ~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.

Loss of floating glacier tongues from the Yelverton Bay region, Ellesmere Island, Canada

ABSTRACTA total of eight floating glacier tongues have shrunk in area by >85% from the Yelverton Bay region of Northern Ellesmere Island since 1959, with unusually large losses since 2005. To better understand the causes of these losses, this study undertakes the first examination of ice tongue changes in this region, including an assessment of changes in surrounding marine ice (i.e. sea ice, sikussak and mélange), and atmospheric and oceanographic forcings. From 1959 to 2017, the total ice tongue area decreased by 49.07 km2, with the majority of this loss occurring from 2005 to 2009 (34.68 km2). The loss of ice tongues since 2005 occurred when open water replaced multi-year landfast sea ice (MLSI) and first-year sea ice in the regions adjacent to the ice tongues. These changes were accompanied by an increase in mean annual mid-depth (i.e. 100 and 200 m) ocean temperatures from −0.29°C from 1999 to 2005 to 0.67°C from 2006 to 2012. Despite the recent return of ocean temperatures to below pre-2006 levels, atmospheric summer temperatures have continued to rise (+0.15°C decade−1 between 1948 and 2016), with open water continuing to occur. Without the sustained presence of MLSI in this region the ice tongues are unable to stabilize, making it unlikely that they will re-form in the current climate.

Area of the Ocean

The area of the ocean, as derived from a new analysis of two digital data sets, is near to 362.5 Mm2 (1Mm2 = 106 km2). The decimal digit is meaningful: uncertainty is about ±0.1 Mm2 or ±0.03%. Although it is impractical to quantify their dominant errors precisely, the ocean areas presented in both of the canonical sources are significantly more uncertain. The often-quoted figure of 361 Mm2 probably derives from the work of Kossinna in 1921 and represents the ocean without the ice shelves and floating glacier tongues, which have an area at present of 1.561 Mm2. The often-quoted figure of 362 Mm2 probably derives from the work of Menard and Smith in 1966 and includes the ice shelves, as it should for the purpose of converting masses of cryospheric or terrestrial water to sea-level equivalent units. However, when Kossinna's estimate is corrected by adding the ice shelves, the two canonical estimates are seen to be inconsistent. The discrepancy implies that measurement errors are much larger than estimated in one source or in both, but Kossinna's estimate, when corrected, agrees much more closely with the modern digital estimates than does the Menard-Smith estimate.

A three-dimensional calving model: numerical experiments on Johnsons Glacier, Livingston Island, Antarctica

AbstractCalving from tidewater glaciers and ice shelves accounts for around half the mass loss from both polar ice sheets, yet the process is not well represented in prognostic models of ice dynamics. Benn and others proposed a calving criterion appropriate for both grounded and floating glacier tongues or ice shelves, based on the penetration depth of transverse crevasses near the calving front, computed using Nye’s formula. The criterion is readily incorporated into glacier and ice-sheet models, but has not been fully validated with observations. We apply a three-dimensional extension of Benn and others’ criterion, incorporated into a full-Stokes model of glacier dynamics, to estimate the current position of the calving front of Johnsons Glacier, Antarctica. We find that two improvements to the original model are necessary to accurately reproduce the observed calving front: (1) computation of the tensile deviatoric stress opening the crevasse using the full-stress solution and (2) consideration of such a tensile stress as a function of depth. Our modelling results also suggest that Johnsons Glacier has a polythermal structure, rather than the temperate structure suggested by earlier studies.

Local response of a glacier to annual filling and drainage of an ice-marginal lake

AbstractIce-marginal Hidden Creek Lake, Alaska, USA, outbursts annually over the course of 2–3 days. As the lake fills, survey targets on the surface of the ‘ice dam’ (the glacier adjacent to the lake) move obliquely to the ice margin and rise substantially. As the lake drains, ice motion speeds up, becomes nearly perpendicular to the face of the ice dam, and the ice surface drops. Vertical movement of the ice dam probably reflects growth and decay of a wedge of water beneath the ice dam, in line with established ideas about jökulhlaup mechanics. However, the distribution of vertical ice movement, with a narrow (50–100 m wide) zone where the uplift rate decreases by 90%, cannot be explained by invoking flexure of the ice dam in a fashion analogous to tidal flexure of a floating glacier tongue or ice shelf. Rather, the zone of large uplift-rate gradient is a fault zone: ice-dam deformation is dominated by movement along high-angle faults that cut the ice dam through its entire thickness, with the sense of fault slip reversing as the lake drains. Survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. The horizontal strain rate also undergoes a reversal across this zone, being compressional as the lake fills, but extensional as the lake drains. Frictional resistance to fault-block motion probably accounts for the fact that lake level falls measurably before the onset of accelerated horizontal motion and vertical downdrop. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.

Precise measurement of changes in ice‐shelf thickness by phase‐sensitive radar to determine basal melt rates

We describe a novel technique for measuring the basal melt rate at a point on an ice shelf. The method uses a phase‐sensitive radar to observe the change in thickness of the ice column between an upper reference horizon and the ice shelf base. The observed thickness change is a combination of basal melting, horizontal ice divergence and firn compaction. The latter two components are determined independently by the repeat survey of surface markers and from estimates of surface accumulation rate and density at the depth of the reference horizon. The technique has been applied at a site on George VI Ice Shelf, Antarctica, where a melt rate of 2.78 ± 0.08 m yr−1 was observed over a twelve‐day period. Our technique is applicable to almost any ice shelf or floating glacier tongue, and its high precision over short time intervals will permit the measurement of seasonal variations in melt rate.

Contribution to the glaciology of northern Greenland from satellite radar interferometry

Interferometric synthetic aperture radar (InSAR) data from the ERS‐1 and ERS‐2 satellites are used to measure the surface velocity, topography, and grounding line position of the major outlet glaciers in the northern sector of the Greenland ice sheet. The mass output of the glaciers at and above the grounding line is determined and compared with the mass input. We find that the grounding line output is approximately in balance with the input, except for the three largest glaciers for which the mass loss is 4±3 km3 ice year−1 or 11±8% of the mass input. Along the coast we detect a systematic retreat of the grounding lines between 1992 and 1996 with InSAR, which implies that the outlet glaciers are thinning. The inferred coastal thinning is too large to be explained by a few warm summers. Glacier thinning must be of dynamic origin, that is, caused by spatial and temporal changes in ice velocity. Iceberg production from the glaciers is uncharacteristically low. It accounts for only 8% of the ice discharge to the ocean. About 55% of the ice is lost through basal melting (5–8 m ice year−1 on average) from the underside of the floating glacier tongues that are in contact with warm ocean waters. Mass losses are highest in the first 10 km of floating ice, where ice reaches the greatest depths and basal melting is 3 times larger than on average. Only a small increase in basal melting would suffice to disintegrate the floating glacier tongues.

Chemical and isotopic profiles from snow pits and shallow firn cores on Campbell Glacier, northern Victoria Land, Antarctica

The chemical (Na+, K+, Mg2+, Ca2+, CH3SO3 − (MSA), Cl− , NO3 − , SO4 2-) and isotopic (δl8O) composition of snow and firn samples from Campbell Glacier, northern Victoria Land, Antarctica, was studied to evaluate the accumulation rate of snow and to investigate the chemical contribution from some emission sources (marine biogenic activity, sea and crust). During the 1994-95 Italian Antarctic Expedition, snow and firn were collected from snow pits and from cores obtained from drilling at three sites (A: 74°41'S, 164°30' E; B: 74°15' S, 164° '04' E; C: 73°45' S, 163°20' E), located ai 50 m (on the floating glacier tongue), 800 m and 1580 m a.s.l., respectively. The mean concentration of sea salt decreased with increasing distance from the coast and with altitude. Generally, the Na+/K+ and Na+/Ca2+ ratios were much lower than the bulk sea-water ratios at sites B and C. The MSA showed mean concentrations (0.27 and 0.17 ¿teq 1 at sites B and C, respectively) consistent with data obtained from other Antarctic sites. The mean concentrations of NO3 ranged from 2.1 μeq 1−1 (site A) to 0.97 μeq1 1 (site C).The mean nss (non-sea-salt) SO4 2-/SO4 2- ratio was -0.055,0.54 and 0.42 at sites A, B and C, respectively. Moreover, the relationship between a2+, nssCa2+, SO4 2- and nssSO4 was quite different at sites B and C. in order to expla in the relationships between the elements and compounds studied at these sites, chemical fractionation and/or reactions inside air masses and différent origin of the air masses at the two sites should be considered. A comparison of the isotopic and chemical profiles was carried out in order to provide a more reliable chronological scale. The chemical and δ18O seasonal variations recorded along the firn cores from the upper site of Campbell Glacier seem to be fairly homogeneous. This made it possible to identify many annual cycles (14-18 years for the 7 m firn core). Using the measured density values, the accumulation rale was also calculated for lower and upper Campbell Glacier. It did not appear to differ between the two sites (150-170 kg m −2a−1 at site B and 140-180 kg m−2a−1at site C) and is in keeping with rates calculated previously for the same area.

Mass Balance of North Greenland

Mass Balance of North Greenland

The Nioghalvfjerdsfjorden glacier project, North-East Greenland: a study of ice sheet response to climatic change

Glaciological research was initiated in 1996 on the floating glacier tongue filling Nioghalvfjerdsfjorden in NorthEast Greenland (Fig. 1), with the aim of acquiring a better understanding of the response of the Greenland ice sheet (Inland Ice) to changing climate, and the implications for future sea level. The research is part of a three year project (1996–98) to advance research into the basic processes that contribute to changes in the ocean volume with a changing climate. Five nations are participants in the project, which is supported by the European Community (EC) Environment and Climate Programme. The Geological Survey of Denmark and Greenland (GEUS) and the Danish Polar Center are the Danish partners in the project, both with integrated research themes concentrated on and around Nioghalvfjerdsfjorden.

Instruments and methods: Submersible remotely operated vehicles (ROVs) for investigations of the glacier-ocean-sediment interface

AbstractSubmersible remotely operated vehicles (ROVs) are valuable research tools for data collection in dangerous or inaccessible environments associated with glaciers terminating in the sea. At tide-water ice cliffs, iceberg calving makes close approaches for extended time periods In manned vessels dangerous. ROVs can be operated from relatively safe distances (hundreds of metres); they can also descend to considerably greater depths (hundreds rather than tens of metres) than scuba diving permits. They can provide data on glacier grounding-line and sea-floor morphology and water-column characteristics (e.g. salinity, turbidity, current velocity). They are also used for. diving under floating glacier tongues and ice shelves where no other access is possible. They can be fitted with a variety of oceanographic sensors, imaging sensors, tracking devices and water and sediment samplers, making them versatile research instruments that can supply qualitative and quantitative data for process studies in logistically difficult environments.

Instruments and methods: Submersible remotely operated vehicles (ROVs) for investigations of the glacier-ocean-sediment interface

AbstractSubmersible remotely operated vehicles (ROVs) are valuable research tools for data collection in dangerous or inaccessible environments associated with glaciers terminating in the sea. At tide-water ice cliffs, iceberg calving makes close approaches for extended time periods In manned vessels dangerous. ROVs can be operated from relatively safe distances (hundreds of metres); they can also descend to considerably greater depths (hundreds rather than tens of metres) than scuba diving permits. They can provide data on glacier grounding-line and sea-floor morphology and water-column characteristics (e.g. salinity, turbidity, current velocity). They are also used for. diving under floating glacier tongues and ice shelves where no other access is possible. They can be fitted with a variety of oceanographic sensors, imaging sensors, tracking devices and water and sediment samplers, making them versatile research instruments that can supply qualitative and quantitative data for process studies in logistically difficult environments.

Observations of the grounding-line area at a floating glacier terminus

A robotic submarine was used for the first observations of a grounding-line area of a floating glacier. The site was Mackay Glacier which terminates as a floating glacier tongue in the Ross Sea, at latitude 77°S. Half of the 20 m thick basal debris layers in Mackay Glacier are deposited as subglacial till in the last 1.8 km that the glacier remains grounded. Subglacial till observed at and beyond the grounding line varies rapidly in texture and rheology spatially, occurring as a flat sheet, as flow-parallel flutes, or as bank forms into which it has been pushed at the grounding line. Very little free- flowing subglacial water was present during the observations, and no major subglacial water discharges appear to have occurred in the past. The other half of the basal debris is melted out up to 1.5 km in front of the grounding line, producing a sheet of glacimarine sediment as shelfstone diamicton and mud draped on subglacial till. Both till and glacimarine sediment may be turbated by icebergs. This simple model of till overlain by shelfstone diamicton and mud is a direct contrast to sedimentary depositional systems at tide-water termini of temperate glaciers.

Observations of the grounding-line area at a floating glacier terminus

A robotic submarine was used for the first observations of a grounding-line area of a floating glacier. The site was Mackay Glacier which terminates as a floating glacier tongue in the Ross Sea, at latitude 77°S. Half of the 20 m thick basal debris layers in Mackay Glacier are deposited as subglacial till in the last 1.8 km that the glacier remains grounded. Subglacial till observed at and beyond the grounding line varies rapidly in texture and rheology spatially, occurring as a flat sheet, as flow-parallel flutes, or as bank forms into which it has been pushed at the grounding line. Very little free- flowing subglacial water was present during the observations, and no major subglacial water discharges appear to have occurred in the past. The other half of the basal debris is melted out up to 1.5 km in front of the grounding line, producing a sheet of glacimarine sediment as shelfstone diamicton and mud draped on subglacial till. Both till and glacimarine sediment may be turbated by icebergs. This simple model of till overlain by shelfstone diamicton and mud is a direct contrast to sedimentary depositional systems at tide-water termini of temperate glaciers.

Glaciomarine sedimentation in Disraeli Fiord, high arctic Canada

Disraeli Fiord represents a glaciomarine environment unique to the north coast of Ellesmere Island, featuring floating glacier tongues, multi-year landfast sea ice and a strongly stratified water body which results from enclosure of the fiord by Ward Hunt Ice Shelf. It is a very low energy depositional environment, even at sites proximal to glaciers. Sediment enters the fiord by interflow and is deposited through suspension settling. Ice rafting is precluded by the year-round sea ice cover. Sedimentation rates in the inner fiord since about 7000 yrs B.P. are estimated to be 5–10 cm/ka, a reflection of the limited sediment influx from the cold-based glaciers which contact the fiord. Changes in sediment structure through the Holocene reflect changes in the rate and process of sediment input as well as changes in fiord circulation, all of which relate to regional climate. During deglaciation (early Holocene) sedimentation rates were orders of magnitude greater than at present. Subglacial meltwater was the dominant source of inflow, with sediment transported in turbid plumes as over- or interflow and deposited through suspension settling. This is supportive of other studies indicating that a pronounced climatic amelioration led to warm-based glaciers at this time.

Gravity anomaly at a Pleistocene lake bed in NW Alaska interpreted by analogy with Greenland's Lake Taserssauq and its floating ice tongue

A possible example of a very deep glacial excavation is provided by a distinctive gravity low located at the front of a valley glacier that once flowed into glacial Lake Aniuk (formerly Lake Noatak) in the western Brooks Range. Geologic and geophysical data suggest that sediments or ice filling a glacially excavated valley are the most probable cause of the 30–50 mGal anomaly. Reasonable choices of geometric models and density contrasts indicate that the former excavation is now filled with a buried‐ice thickness of 700 m or sediment thicknesses greater than 1 km; comparable anomalies are not known for other glaciated lacustrine valleys. However, many fiords do exceed 1 km in depth, and Crary found one nearly 2 km deep in Antarctica. In studying this fiord, he suggested the probable increased efficiency of excavation directly behind the point where an outlet glacier becomes afloat to form the Ross Ice Shelf and where it thus has a vertical component of motion and a mechanism for debris removal. Floating glacier ice tongues are now rare in the Arctic, but they exist in maritime parts of northern Ellesmere Island and Greenland. Studies of ice movement, environment, and morphology of another large floating glacier tongue in a perennially frozen lake in the Angiussaq Mountains of northern Greenland suggest that Pleistocene Lake Aniuk could have had a similar environment, water temperature, and near‐stable water level and that it could have maintained both a floating polar glacier tongue and a perennial ice cover. No direct evidence of efficient excavation was observed in Greenland, but efficient glacial erosion behind a floating polar ice tongue could explain the excavation that caused the Alaskan gravity anomaly.

Portrait of an Antarctic outlet glacier

ABSTRACT The Hays Glacier of Enderby Land is a small Antarctic outlet glacier with a “sack-shape” source region of as yet not exactly known southward extent and area (approximately 104km2). It has a uniform or slightly wavy longitudinal profile, an approximately 7 km wide calving front between 46°15’ and 46°20′E, and a partly floating glacier tongue, extending to the seasonally changing front (classification 424 118 according to UNESCO-IAHS, 1970). The longitudinal mean surface slopes are 5–8 m km−1 on the tongue, 20–30 m km−1 in the step-shaped central section, and 8–12 m km−1 in the entrance region. The glacier is bordered to 15 km south of the front by about 500-m-wide serac belts, associated in some places with pressure ridges. It is distinctly separated from the continental ice sheet by three rock walls on the eastern edge. At the western edge the glacier has a secondary influx region of 40 km3 area which is crevassed and feeds a well-defined tributary into the left part of the glacier tongue. The av...

Floating Glacier Tongue from Mount Erebus

Floating Glacier Tongue from Mount Erebus