We collected ~1300 km of ground-penetrating radar profiles over McMurdo Ice Shelf, Antarctica, using frequencies between 40 and 400 MHz to determine extent, continuity and depth to the brine. We also used profiles to determine meteoric ice thickness and locate englacial features, which may suggest ice shelf instability. The brine extends 9–13 km inland from the ice shelf terminus and covers the entire region between Ross, White and Black Islands. Jump unconformities and basal fractures exist in the brine and ice shelf, respectively, suggesting prior fracturing and re-suturing. One 100 MHz profile, the most distal from the ice shelf edge while still being situated over the brine, simultaneously imaged the brine and bottom of meteoric ice. This suggests a negative brine salinity gradient moving away from the terminus. The meteoric ice bottom was also imaged in a few select locations through blue ice in the ablation zone near Black Island. We suggest that brine, sediment-rich ice and poor antenna coupling on rough ice attenuates the signal in this area. When combined with other recent mass-balance and structural glaciology studies of MIS, our results could contribute to one of the most high-resolution physical models of an ice shelf in Antarctica.

Ocean tides influence the flow of marine-terminating glaciers. Observations indicate that the large fortnightly variations in ice flow at Rutford Ice Stream in West Antarctica originate in the floating ice shelf. We show that nonlinear variations in ice shelf buttressing driven by tides can produce such fortnightly variations in ice flow. These nonlinearities in the tidal modulation of buttressing stresses can be caused by asymmetries in the contact stress from migration of the grounding line and bathymetric pinning points beneath the ice shelf. Using a simple viscoelastic model, we demonstrate that a combination of buttressing and hydrostatic stress variations can explain a diverse range of tidal variations in ice shelf flow, including the period, phase and amplitude of flow variations observed at Rutford and Bindschadler Ice Streams.

Ross Ice Shelf (RIS) is known to experience transient thickness change due to changes in the flow of its tributary ice streams and glaciers and this may complicate identification of external, climate-forced signals in contemporary observations of ice shelf thinning and thickening. Flux changes at the lateral boundaries produce both instantaneous and longer timescale adjustments in the coupled velocity and thickness fields. Here, we adapt a statistical approach to output from a numerical model of ice shelf flow to identify characteristic patterns (spatial response surfaces) associated with stepped and cyclic perturbations to boundary fluxes. Once known, characteristic patterns identified in observational data may be attributed to specific sources. An example involving discharge of Byrd Glacier into RIS is described. We find that spatial response surfaces for thickness and velocity generated in individual flow model experiments appear to be independent of flux perturbation shape and magnitude. Additionally, recent acceleration of Byrd Glacier is apparent in ICESat-detected change in RIS thickness.

Information on the occurrence, spatial distribution and morphometric characteristics of Antarctic icebergs is needed in a large number of applications including navigation, heat and freshwater balance calculations, biochemistry of the ocean and climatology. Using over 60 000 ship observations of icebergs in the Southern Ocean collected since the end of the 1940s we have produced a detailed map of the distribution of Antarctic icebergs as well as maps of related statistics including the standard deviation, minimum and maximum values of the iceberg concentration and the probability of iceberg-free observations. The study incorporated small and medium-sized icebergs with a length of <10 nautical miles. Most observations were taken during the warm period of the year, from December to April. It is shown that the iceberg distribution across the Southern Ocean is determined by the location of calving regions and peculiarities of the atmospheric circulation and ocean currents. Iceberg concentration data combined with information on the iceberg size and shape distribution have been used to evaluate the area-integrated characteristics of Antarctic icebergs. The instantaneous number of icebergs in the Southern Ocean was estimated as 132 269 with an uncertainty of 7%. The area and volume of icebergs were equal correspondingly to 55 805 km2 and 16 893 km3 with uncertainties of 32–33%.

Measurements made by an underwater glider deployed near the Ross Ice Shelf were used to identify the presence of Ice Shelf Water (ISW), which is defined as seawater with its potential temperature lower than its surface freezing point temperature. Properties logged by the glider included in situ temperature, electrical conductivity, pressure, GPS location at surfacings and time. For most of the first 30 recorded dives of its deployment, evidence suggests the glider was prevented from surfacing due to being under the ice shelf. For dives under the ice shelf, farthest from the ice shelf front, ISW layers of varying thicknesses and depth locations were observed; between 2 m thick (centred at 231 m depth) to >93 m thick (centred at >360 m). For dives under the ice shelf, close to the ice shelf front, either no ISW was observed or ISW layers were centred at shallower depths (116–127 m). Thicker ISW layers (e.g. up to 250 m thickness centred at 421 m) were observed for some glider dives in open water in front of the Ross Ice Shelf. No in situ supercooling (water colder than the pressure-dependent freezing point temperature) was observed.

The Drygalski Ice Tongue presents an ~80 km long floating obstacle to alongshore flows in the Victoria Land coastal ocean region of the Western Ross Sea. Here we use oceanographic data from near to the tongue to explore the interplay between the floating glacier and the local currents and stratification. A vessel-based circuit of the glacier, recording ocean temperature and salinity profiles, reveals the southwest corner to be the coldest and most complex in terms of vertical structure. The southwest corner structure beneath the surface warm, salty layer sustains a block of very cold water extending to 200 m depth. In this same location there was a distinct layer at 370 m not seen anywhere else of water at ~−1.93°C. The new observations broadly, but not directly, support the presence of a coherent Victoria Land Coastal Current. The data suggest the northward moving coastal current turns against the Coriolis force and works its way anticlockwise around the glacier, but with leakage beneath the glacier through the highly ‘rippled’ underside, resulting in a spatially heterogeneous supply to the Terra Nova Bay Polynya region – an important location for the formation of high-salinity shelf water.

Calving is a complex process subject to several cooperating atmospheric, oceanographic and glaciological forcings that vary in space and time, and whose relative effects are challenging to separate. Statistical ‘Systems Analysis’ is commonly used in engineering and economics to extricate complex ‘force–response’ relationships. Here we apply Systems Analysis to the Amery rift system, East Antarctica. We develop a scalable ‘System Model’ driven by a coarsely-sampled dataset characteristic of glaciological observations in remote locations, and validate it using rift lengths observed in 2000–06 and 2012. In this initial demonstration, we forecast a detachment date of ~2019 ± 5 years for the large tabular iceberg colloquially known as the ‘Loose Tooth’, for which relative humidity surprisingly emerges as the best statistical predictor. RACMO2 climate modelling reveals that relative humidity correlates best with surface albedo and snowmelt, both of which are intimately linked to firn compaction and ice shelf temperature and flow. We postulate that relative humidity can therefore serve as a proxy for internal stress, a known key control of ‘Loose Tooth’ calving. Although no physical causality is implied in Systems Analysis, postulates such as this can aid in setting priorities in studies of complex glaciological processes.

Accelerated discharge through marine-terminating outlet glaciers has been a key component of the rapid mass loss from Arctic glaciers since the 1990s. However, glacier retreat and its climatic controls have not been assessed at the pan-Arctic scale. Consequently, the spatial and temporal variability in the magnitude of retreat, and the possible drivers are uncertain. Here we use remotely sensed data acquired over 273 outlet glaciers, located across the entire Atlantic Arctic (i.e. areas potentially influenced by North Atlantic climate and/or ocean conditions, specifically: Greenland, Novaya Zemlya, Franz Josef Land and Svalbard), to demonstrate high-magnitude, accelerating and near-ubiquitous retreat between 1992 and 2010. Overall, mean retreat rates increased by a factor of 3.5 between 1992 and 2000 (−30.5 m a−1) and 2000–10 (−105.8 m a−1), with 97% of the study glaciers retreating during the latter period. The Retreat was greatest in northern, western and south-eastern Greenland and also increased substantially on the Barents Sea coast of Novaya Zemlya. Glacier retreat showed no significant or consistent relationship with summer air temperatures at decadal timescales. The rate of frontal position change showed a significant, but weak, correlation with changes in sea-ice concentrations. We highlight large variations in retreat rates within regions and suggest that fjord topography plays an important role. We conclude that marine-terminating Arctic outlet glaciers show a common response of rapid and accelerating retreat at decadal timescales.

Icebergs calved from tidewater glaciers represent about one third to one half of the freshwater flux from the Greenland ice sheet to the surrounding ocean. Using multiple satellite datasets, we quantify the first fjord-wide distributions of iceberg sizes and characteristics for three fjords with distinct hydrography and geometry: Sermilik Fjord, Rink Isbræ Fjord and Kangerlussuup Sermia Fjord. We estimate average total iceberg volumes in summer in the three fjords to be 6.4 ± 1.5, 1.7 ± 0.40 and 0.16 ± 0.09 km3, respectively. Iceberg properties are influenced by glacier calving style and grounding line depth, with variations in size distribution represented by exponents of power law distributions that are −1.95 ± 0.06, −1.87 ± 0.05 and −1.62 ± 0.04, respectively. The underwater surface area of icebergs exceeds the subsurface area of glacial termini by at least one order of magnitude in all three fjords, underscoring the need to include iceberg melt in fjord freshwater budgets. Indeed, in Sermilik Fjord, we calculate summertime freshwater flux from iceberg melt of 620 m3 s−1 (±140 m3 s−1), similar in magnitude to subglacial discharge. The method developed here can be extended across Greenland to assess relationships between glacier calving, iceberg discharge and freshwater production.

Jakobshavn Isbræ, which terminates in Ilulissat Icefjord, has undergone rapid retreat and is currently the largest contributor to ice-sheet mass loss among Greenland's marine terminating glaciers. Accelerating mass loss is increasing fresh water discharge to the ocean, which can feed back on ice melt, impact marine ecosystems and potentially modify regional and larger scale ocean circulation. Here we present hydrographic observations, including inert geochemical tracers, that allow the first quantitative description of the glacially-modified waters exported from the Jakobshavn/Icefjord system. Observations within the fjord suggest a deep-reaching overturning cell driven by glacial buoyancy forcing. Modified waters containing submarine meltwater (up to 2.5 ± 0.12%), subglacial discharge (up to 6 ± 0.37%) and large portions of entrained ocean waters are seen to exit the fjord and flow north. The exported meltwaters form a buoyant coastal gravity current reaching to 100 m depth and extending 10 km offshore.

Significant intra-annual variability in flow rates of tidewater-terminating Arctic glaciers has been observed in recent years. These changes may result from oceanic and/or atmospheric forcing through (1) perturbations at the terminus, such as enhanced submarine melt and changes in sea-ice buttressing, or (2) increased surface melt, in response to atmospheric warming, reaching the bed and promoting glacier slip. We examine the influence of these processes on Belcher Glacier, a large fast-flowing tidewater outlet of the Devon Island ice cap in the Canadian Arctic. A hydrologically-coupled higher-order ice flow model is used to estimate changes in glacier flow speed as a result of changes in sea-ice buttressing and hydrologically-driven melt-season dynamics. Daily run-off from five sub-catchments over the 2008 and 2009 melt seasons provides meltwater forcing for the model simulations. Model results are compared with remotely-sensed and in situ ice-surface velocity measurements. Sea-ice effects are found to have a minor influence on glacier flow speed relative to that of meltwater drainage, which is clearly implicated in short-term velocity variations during the melt season. We find that threshold drainage is essential in determining the timing of these short-lived accelerations.

Breiðamerkurjökull flows from the Vatnajökull ice cap and calves into the Jökulsárlón proglacial lagoon. The lagoon is connected to the North Atlantic Ocean through a 6 m deep narrow channel. Four hydrographic surveys in spring 2012, and a 2011 4-month long temperature and salinity time series of lagoon inflow show that the lake has significantly changed since 1976. Warm saline ocean water enters each tidal cycle and descends below the maximum sampled depths. The lagoon has a surface layer of ice melt, freshwater and Atlantic derived water. Beneath 10 m depth an advective/diffusive balance is responsible for determining the temperature and salinity of the lagoon waters down to ~90 m. To maintain the observed hydrographic structure, we calculate an upwelling of deep water of ~0.2 m d−1. A survey within 30 m of Breiðamerkurjökull showed that the warmest and most saline waters sampled within the lagoon below 10 m depth were adjacent to the glacier face, along with multiple interleaved warm and cold layers. A heat and salt balance model shows that submarine melting along the ice face generates multiple meltwater plumes that are mixed and diluted within 200 m of the ice face.

This study reviews the effects of a force acting upon ice shelves and icebergs arising from the oblateness of the Earth's geoid and the displacement between the center of mass and the center of buoyancy for an object floating on water. The force has been introduced earlier as Polfluchtkraft or ‘pole-fleeing force’ by Alfred Wegener and others in the context of continental drift, but it is here applied to floating ice for the first time. It propels icebergs towards the equator, but also tugs on ice shelves making them more likely to break apart in a warming climate with possible consequences for the entire ice sheet.