Поверхностные скорости и айсберговый сток ледникового купола Академии Наук на Северной Земле

We have determined the ice-surface velocities of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, during the period November 2016 – November 2017, using intensity offset-tracking of Sentinel-1 synthetic-aperture radar images. We used the average of 54 pairs of weekly velocities (with both images in each pair separated by a12-day period) to estimate the mean annual ice discharge from the ice cap. We got an average ice discharge for 2016–2017 of 1,93±0,12 Gt a−1, which is equivalent to −0,35±0,02 m w.e. a−1 over the whole area of the ice cap. The difference from an estimate of ~1,4 Gt a−1 for 2003–2009 can be attributed to the initiation of ice-stream flow in Basin BC sometime between 2002 and 2016. Since the front position changes between both periods have been negligible, ice discharge is equivalent to calving flux. We compare our results for calving flux with those of previous studies and analyse the possible drivers of the changes observed along the last three decades. Since these changes do not appear to have responded to environmental changes, we conclude that the observed changes are likely driven by the intrinsic characteristics of the ice cap governing tidewater glacier dynamics.По 54 парам космических снимков Sentinel‐1, сделанных с ноября 2016 г. по ноябрь 2017 г., определены скорости движения ледникового купола Академии Наук на Северной Земле. На этой основе оценён среднегодовой расход льда в море этого купола (1,93±0,12 Гт/год), установлены основные пути стока льда, проведено сравнение с прежними оценками

Processes and patterns of glacier-influenced sedimentation and recent tidewater glacier dynamics in Darbel Bay, western Antarctic Peninsula

AbstractBathymetric data of unprecedented resolution are used to provide insights into former ice dynamics and glacial processes in a western Antarctic Peninsula embayment. An assemblage of submarine glacial landforms, which includes subglacially produced streamlined features and ice-marginal ridges, reveals the former pattern of ice flow and retreat. A group of more than 250 small (< 1–3 m high, 10–20 m wide) and relatively evenly spaced recessional moraines was identified beyond the margin of Philippa Glacier. The small recessional moraines are interpreted to have been produced during short-lived, possibly annual re-advances of a grounded ice margin during overall retreat. This is the first time that these features have been shown to be part of the assemblage of landforms produced by tidewater glaciers on the Antarctic Peninsula. Glacier-terminus changes during the last four decades, mapped from LANDSAT satellite images, were analysed to determine whether the moraines were produced during recent still-stands or re-advances of Philippa Glacier and to further investigate the short-term (annual to decadal) variability in ice-marginal position in tidewater glacier systems. The asynchronous response of individual tidewater glaciers in Darbel Bay is interpreted to be controlled mainly by local topography rather than by glacier catchment-area size.C.L. Batchelor was in receipt of a Junior Research Fellowship from Newnham College, Cambridge during this work. K.A Hogan and R.D Larter are supported by the Polar Science for Planet Earth programme funded by the Natural Environment Research Council, U.K

Submarine Moraines in Southeast Greenland Fjords Reveal Contrasting Outlet-Glacier Behavior since the Last Glacial Maximum

Knowledge of the past behavior of the outlet glaciers of Southeast (SE) Greenland is necessary to understand and model spatial differences in the response of the Greenland Ice Sheet (GIS) to climatic changes. Here we use bathymetric data to map the distribution of more than 50 major moraines in SE Greenland fjords. Inner-fjord moraines are widespread along the SE Greenland margin, occurring in 65% of the surveyed fjords. We identify, for the first time, nine midfjord moraines that span the approximately 150-km-long eastern margin of the Julianehåb Ice Cap. In contrast, midfjord moraines are generally absent from the deeper and wider fjords of the SE GIS. The variable distribution of midfjord moraines along the SE Greenland margin reveals contrasting behavior of the SE GIS and the eastern Julianehåb Ice Cap during the last deglaciation, which probably reflects differences in fjord geometry and exposure to ocean heat

A tidewater glacier landform assemblage in Belcher Inlet, Canadian Arctic

Belcher Glacier, a 35 km-long tidewater outlet glacier of the 12,000 km² ice cap on Devon Island (Dowdeswell et al. 2004), is one of the fastest-flowing glaciers in the Canadian Arctic (Van Wychen et al. 2014) (Fig. 1). Belcher Glacier and neighbouring Fitzroy Glacier to the southeast account for about 55% of the iceberg calving loss from the Devon Ice Cap (Van Wychen et al. 2014). The terminus of Belcher Glacier remained relatively stable between the 1960s (light blue dashed line in Fig. 1a) and 2000 (Landsat 7 satellite image in Fig. 1a). In contrast, the unnamed glacier immediately to the north retreated 2 km during this period (Fig. 1a). Belcher Glacier and the unnamed glacier retreated around 500 m and 250 m, respectively, between 2000 and 2014 (dark blue dashed line in Fig. 1a). The bed topography of Belcher Glacier, which is around 250 m below sea level at the present-day glacier margin (Fig. 1c) and remains below sea level in the lower 11 km of the glacier, suggests that its terminus region may become unstable in the event of future retreat. Seafloor mapping of Belcher Inlet beyond the termini of Belcher Glacier and the unnamed glacier (Fig. 1a), together with sub-bottom profiling, provide information about the dynamic behaviour of tidewater glaciers.This is the author accepted manuscript. The final version is available from Geological Society of London via https://doi.org/10.1144/M46.14

Derivation of Del180 from sediment core log data\u27 Implications for millennial-scale climate change in the Labrador Sea

Sediment core logs from six sediment cores in the Labrador Sea show millennial-scale climate variability during the last glacial by recording all Heinrich events and several major Dansgaard-Oeschger cycles. The same millennial-scale climate change is documented for surface water δ18O records of Neogloboquadrina pachyderma (left coiled); hence the surface water δ18O record can be derived from sediment core logging by means of multiple linear regression, providing a paleoclimate proxy record at very high temporal resolution (70 years). For the Labrador Sea, sediment core logs contain important information about deepwater current velocities and also reflect the variable input of ice-rafted debris from different sources as inferred from grain-size analysis, the relation of density and P wave velocity, and magnetic susceptibility. For the last glacial, faster deepwater currents, which correspond to highs in sediment physical properties, occurred during iceberg discharge and lasted from several centuries to a few millennia. Those enhanced currents might have contributed to increased production of intermediate waters during times of reduced production of North Atlantic Deep Water. Hudson Strait might have acted as a major supplier of detrital carbonate only during lowered sea level (greater ice extent). During coldest atmospheric temperatures over Greenland, deepwater currents increased during iceberg discharge in the Labrador Sea, then surface water freshened shortly thereafter, while the abrupt atmospheric temperature rise happened after a larger time lag of ≥ 1 kyr. The correlation implies a strong link and common forcing for atmosphere, sea surface, and deep water during the last glacial at millennial timescales but decoupling at orbital timescales

A persistent Norwegian Atlantic Current through the Pleistocene glacials

Changes in ocean‐circulation regimes in the northern North Atlantic and the Nordic Seas may affect not only the Arctic but potentially hemispheric or even global climate. Therefore, unraveling the long‐term evolution of the North Atlantic Current‐Norwegian Atlantic Current system through the Pleistocene glaciations could yield useful information and climatological context for understanding contemporary changes. In this work, ~50,000 km2 of 3‐D seismic reflection data are used to investigate the Pleistocene stratigraphy for evidence of paleo‐oceanographic regimes on the mid‐Norwegian margin since 2.58 Ma. Across 33 semicontinuous regional paleo‐seafloor surfaces ~17,500 iceberg scours have been mapped. This mapping greatly expands our spatiotemporal understanding of currents and iceberg presence in the eastern Nordic Seas. The scours display a dominant southwest‐northeast trend that complements previous sedimentological and numerical modeling studies that suggest northward‐flowing currents in the Norwegian Sea during the Pleistocene. This paleo‐oceanographic study suggests that through many of the Pleistocene glaciations, the location of surface ocean currents in the Norwegian Sea and, by extension, the eastern North Atlantic, were broadly similar to the present

Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks.

Marine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat becomes unstable (marine ice-sheet instability) and thus accelerates. It is thought that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth and drift direction. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today, which would produce wide, flat-based plough marks or toothcomb-like multi-keeled plough marks. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers of icebergs smaller than the typical tabular icebergs produced today. Our findings demonstrate the effective operation of MICI in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet

Ice-stream stability on a reverse bed slope

Marine-based ice streams whose beds deepen inland are thought to be inherently unstable. This instability is of particular concern because significant portions of the marine-based West Antarctic and Greenland ice sheets are losing mass and their retreat could contribute significantly to future sea-level rise. However, the present understanding of ice-stream stability is limited by observational records that are too short to resolve multi-decadal to millennial-scale behaviour or to validate numerical models8. Here we present a dynamic numerical simulation of Antarctic ice-stream retreat since the Last Glacial Maximum (LGM), constrained by geophysical data, whose behaviour is consistent with the geomorphological record. We find that retreat of Marguerite Bay Ice Stream following the LGM was highly nonlinear and was interrupted by stabilizations on a reverse-sloping bed, where theory predicts rapid unstable retreat. We demonstrate that these transient stabilizations were caused by enhanced lateral drag as the ice stream narrowed. We conclude that, as well as bed topography, ice-stream width and long-term retreat history are crucial for understanding decadal- to centennial-scale ice-stream behaviour and marine ice-sheet vulnerability