scholarly journals GRACE constraints on Earth rheology of the Barents Sea and Fennoscandia

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 379-395
Author(s):  
Marc Rovira-Navarro ◽  
Wouter van der Wal ◽  
Valentina R. Barletta ◽  
Bart C. Root ◽  
Louise Sandberg Sørensen
Keyword(s):  
Solid Earth ◽  
Upper Mantle ◽  
Barents Sea ◽  
Ice Sheet ◽  
Last Glacial ◽  
Lithospheric Thickness ◽  
Mantle Viscosity ◽  
The Barents Sea ◽  
Grace Data ◽  
The Last Glacial

Abstract. The Barents Sea is situated on a continental margin and was home to a large ice sheet at the Last Glacial Maximum. Studying the solid Earth response to the removal of this ice sheet (glacial isostatic adjustment; GIA) can give insight into the subsurface rheology of this region. However, because the region is currently covered by ocean, uplift measurements from the center of the former ice sheet are not available. The Gravity Recovery and Climate Experiment (GRACE) gravity data have been shown to be able to constrain GIA. Here we analyze GRACE data for the period 2003–2015 in the Barents Sea and use the data to constrain GIA models for the region. We study the effect of uncertainty in non-tidal ocean mass models that are used to correct GRACE data and find that it should be taken into account when studying solid Earth signals in oceanic areas from GRACE. We compare GRACE-derived gravity disturbance rates with GIA model predictions for different ice deglaciation chronologies of the last glacial cycle and find that best-fitting models have an upper mantle viscosity equal or higher than 3×1020 Pa s. Following a similar procedure for Fennoscandia we find that the preferred upper mantle viscosity there is a factor 2 larger than in the Barents Sea for a range of lithospheric thickness values. This factor is shown to be consistent with the ratio of viscosities derived for both regions from global seismic models. The viscosity difference can serve as constraint for geodynamic models of the area.

scholarly journals GRACE constraints on Earth rheology of the Barents Sea and Fennoscandia

2019 ◽  
Author(s):  
Marc Rovira-Navarro ◽  
Wouter van der Wal ◽  
Valentina R. Barletta ◽  
Bart C. Root ◽  
Louise Sandberg Sørensen
Keyword(s):  
Solid Earth ◽  
Upper Mantle ◽  
Barents Sea ◽  
Ice Sheet ◽  
Lithospheric Thickness ◽  
Isostatic Adjustment ◽  
Mantle Viscosity ◽  
The Barents Sea ◽  
Grace Data ◽  
Geodynamic Models

Abstract. The Barents Sea is situated on a continental margin and was home to a large ice sheet at the Last Glacial Maximum. Studying the solid Earth response to the removal of this ice sheet (Glacial Isostatic Adjustment, GIA) can give insight in the sub-surface structure in this region. However, because the region is currently covered by ocean, uplift measurements from the center of the former ice sheet are not available, but GRACE data has been shown to be able to constrain GIA. Here we analyze GRACE data for the period 2003–2015 in the Barents Sea and use it to constrain a GIA models for the region. We study the effect of uncertainty in non-tidal ocean mass models that are used to correct GRACE data and find that it is not negligible and should be taken into account when studying solid Earth signals in oceanic areas from GRACE. We compare the obtained gravity rates with GIA model predictions for different ice deglaciation chronologies and infer a lower bound for the Earth's upper mantle viscosity of 2·1020 Pa·s. Following a similar procedure for Fennoscandia we find that the preferred upper mantle viscosity there is a factor 2 larger than in the Barents Sea for a range of lithospheric thickness values. This factor is shown to be consistent with the ratio of viscosities derived for both regions from global seismic models. The viscosity difference can serve as constraint for geodynamic models of the area.

Methane hydrate mobilization by ice stream erosion during the last glacial

2020 ◽  
Author(s):  
Pavel Serov ◽  
Henry Patton ◽  
Malin Waage ◽  
Calvin Shackleton ◽  
Jurgen Mienert ◽  
...  
Keyword(s):  
Gas Hydrate ◽  
Methane Hydrate ◽  
Barents Sea ◽  
Ice Sheet ◽  
Permafrost Degradation ◽  
Last Glacial ◽  
The Barents Sea ◽  
Ice Stream ◽  
Geophysical Imaging ◽  
The Last Glacial

<p>During the past ~2.6 Ma, some 30 glaciations have caused episodic high pressure and low temperature conditions and forced growth and decay of extensive subglacial methane hydrate accumulations globally. Research on Arctic methane release has primarily focused on warm, interglacial episodes when hydrates became unstable across territories either abandoned by former ice sheets or affected by permafrost degradation. Here we present a new mechanism – the subglacial erosion of gas hydrate-bearing sediments – that actively mobilizes methane in hydrate and dissolved form and delivers it to the ice sheet margin. We investigate this mechanism using geophysical imaging and ice sheet/gas hydrate modeling focused on a study site in Storfjordrenna, that hosted large ice stream draining the Barents Sea ice sheet. During the last glacial, we find that this ice stream overrode an extensive cluster of conduits that supplied a continuous methane flux from a deep, thermogenic source and delivered it to the subglacial environment. Our analysis reveals that 15,000 to 44,000 m<sup>3</sup> of gas hydrates were subglacially eroded from the 17 km<sup>2</sup> study site and transported to the shelf-edge. Given the abundance of natural gas reservoirs across the Barents Sea and marine-based glaciated petroleum provinces elsewhere, we propose that this mechanism had the potential to mobilize a substantial flux of subglacial methane throughout multiple Quaternary glacial episodes.</p>

THE LAST GLACIAL MAXIMUM OF SVALBARD AND THE BARENTS SEA AREA: ICE SHEET EXTENT AND CONFIGURATION

1998 ◽  
Vol 17 (1-3) ◽  
pp. 43-75 ◽  
Author(s):  
JON Y. LANDVIK ◽  
STEIN BONDEVIK ◽  
ANDERS ELVERHØI ◽  
WILLY FJELDSKAAR ◽  
JAN MANGERUD ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Barents Sea ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The Barents Sea ◽  
Sea Area ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Upper mantle viscosity structure and lithospheric thickness of Antarctica inferred from recent seismic models

2020 ◽  
Author(s):  
Douglas Wiens ◽  
Andrew Lloyd ◽  
Weisen Shen ◽  
Andrew Nyblade ◽  
Richard Aster ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Upper Mantle ◽  
Ice Sheet ◽  
West Antarctica ◽  
Lithospheric Thickness ◽  
Isostatic Adjustment ◽  
Low Viscosity ◽  
Mantle Viscosity ◽  
Seismic Models ◽  
The Antarctic

<p>Upper mantle viscosity structure and lithospheric thickness control the solid Earth response to variations in ice sheet loading. These parameters vary significantly across Antarctica, leading to strong regional differences in the timescale of glacial isostatic adjustment (GIA), with important implications for ice sheet models.  We estimate upper mantle viscosity structure and lithospheric thickness using two new seismic models for Antarctica, which take advantage of temporary broadband seismic stations deployed across Antarctica over the past 18 years. Shen et al. [2018] use receiver functions and Rayleigh wave velocities from earthquakes and ambient noise to develop a higher resolution model for the upper 200 km beneath Central and West Antarctica, where most of the seismic stations have been deployed. Lloyd et al [2019] use full waveform adjoint tomography to invert three-component earthquake seismograms for a radially anisotropic model covering Antarctica and adjacent oceanic regions to 800 km depth. We estimate the mantle viscosity structure from seismic structure using laboratory-derived relationships between seismic velocity, temperature, and rheology. Choice of parameters for this mapping is guided in part by recent regional estimates of mantle viscosity from geodetic measurements. We also describe and compare several different methods of estimating lithospheric thickness from seismic constraints.</p><p>The mantle viscosity estimates indicate regional variations of several orders of magnitude, with extremely low viscosity (< 10<sup>19</sup> Pa s) beneath the Amundsen Sea Embayment (ASE) and the Antarctic Peninsula, consistent with estimates from GIA models constrained by GPS data.  Lithospheric thickness is also highly variable, ranging from around 60 km in parts of West Antarctica to greater than 200 km beneath central East Antarctica. In East Antarctica, several prominent regions such as Dronning Maude Land and the Lambert Graben show much thinner lithosphere, consistent with Phanerozoic tectonic activity and lithospheric disruption. Thin lithosphere and low viscosity between the ASE and the Antarctic Peninsula likely result from the thermal effects of the slab window as the Phoenix-Antarctic plate boundary migrated northward during the Cenozoic. Low viscosity regions beneath the ASE and Marie Byrd Land coast connect to an offshore anomaly at depths of ~ 250 km, suggesting larger-scale thermal and geodynamic processes that may be linked to the initial Cretaceous rifting of New Zealand and Antarctica. Low mantle viscosity results in a characteristic GIA time scale on the order of several hundred years, such that isostatic adjustment occurs on the same time scale as grounding line retreat.  Thus the associated rebound may lessen the effect of the marine ice sheet instability proposed for the ASE region. </p>

Depositional environments in the northern Barents Sea, from the last glacial to the present — preliminary results

2021 ◽  
Author(s):  
Vårin Trælvik Eilertsen ◽  
Rydningen Tom Arne ◽  
Matthias Forwick ◽  
Monica Winsborrow ◽  
Jan Sverre Laberg
Keyword(s):  
Sea Ice ◽  
Environmental Changes ◽  
Barents Sea ◽  
Ice Sheet ◽  
Depositional Environments ◽  
Radiocarbon Dates ◽  
Future Evolution ◽  
Last Glacial ◽  
Minimum Age ◽  
The Last Glacial

<p>The Eurasian Ice Sheet Complex was the world’s third largest ice mass during the last glacial maximum (LGM), and included the British, Fennoscandian and Svalbard–Barents Sea ice sheets. Of these three, the mostly marine-based Svalbard-Barents Sea Ice Sheet (SBIS) is the least well constrained in terms of ice sheet dynamics and deglacial retreat patterns. Improving the understanding of the behavior and decay of this marine paleo-ice sheet can provide knowledge that is relevant to understanding the future evolution of the marine terminating ice margins in Greenland and Antarctica, which are today undergoing rapid retreat and thinning.</p><p>We present high-resolution TOPAS sub-bottom profiler data and multi-proxy analyses of four sediment gravity cores (1.15 to 5.05 m long) retrieved from water depths of c. 250-550 m in a trough south of Kvitøya, NW Barents Sea. The data were collected during the Nansen Legacy (https:/arvenetternansen.com/) Paleo-cruise in 2018, with the aim of reconstructing the patterns and timing of deglaciation of the SBIS and postglacial environmental changes in the northern Barents Sea. The data show a succession of up to 10 m high and 400 m wide ridges, interpreted to be recessional push-moraines, representing small still-stands or re-advances of the ice front during its retreat in southwesterly direction. An up to 40 m high and 20 km long sedimentary wedge in the central and western part of the study area buries some of these moraines. This wedge is interpreted to be a grounding zone wedge representing a major still-stand or re-advance during the deglaciation.</p><p>The gravity cores are located distal to, on the distal slope and on top of the grounding zone wedge. A muddy diamict defines the lowermost unit in each core. It is interpreted to be primarily subglacial till. This till is covered by laminated mud, interpreted to represent sedimentation from meltwater plumes that emanated from the nearby ice margin. Massive marine mud containing scattered clasts (the clasts are interpreted to be ice rafted debris) define the uppermost unit in all cores. This is suggested to represent deposition from suspension settling and ice rafting in a glacier-distal environment at the end of the last glacial, as well as during modern conditions.</p><p>Radiocarbon dates (submitted for dating) will provide a minimum age for the formation of the grounding zone wedge and the recessional moraines in front of it. This will improve the chronology on the deglacial events forming these deposits and landforms. Together with detailed multi-proxy analyses of the sedimentary units, this will also provide new knowledge about the development from glacial conditions to a glacier-proximal and –distal, and an open marine environment from the last glacial to the present.</p>

Fennoscandian Ice Sheet glaciation in northwest Arctic Russia during the Last Glacial-Interglacial Transition

2021 ◽  
Author(s):  
Benjamin Boyes ◽  
Danni Pearce ◽  
Lorna Linch
Keyword(s):  
High Resolution ◽  
Kola Peninsula ◽  
Marginal Zone ◽  
Barents Sea ◽  
Ice Sheet ◽  
Last Glacial ◽  
Geomorphological Mapping ◽  
Ice Sheet Dynamics ◽  
Arctic Russia ◽  
The Last Glacial

<p>Previous attempts to reconstruct the glacial history of the last Fennoscandian Ice sheet (FIS) in northwest Arctic Russia have resulted in various Last Glacial-Interglacial Transition (c. 20-10 ka) scenarios, suggesting that the Kola Peninsula was glaciated by the FIS, the Ponoy Ice Cap, or the Kara Sea Ice Sheet. The conflicting glacial interpretations have stemmed, in part, from the use of low-resolution geomorphological and geological maps. The advent of high-resolution remotely-sensed imagery warrants a new glacial reconstruction of ice sheet dynamics in northwest Arctic Russia: we therefore present initial glacial interpretations based on new high-resolution geomorphological mapping.</p><p>Geomorphological mapping using high-resolution ArcticDEM and PlanetScope imagery has identified >245,000 glacial landforms, significantly increasing the volume and detail of geomorphological data in the region. Over 66,000 subglacial bedforms (subglacial lineations and subglacial ribs) are used to construct flowsets, which demonstrate that ice flowed from the Scandinavian mountains in the west and across the shield terrain of the Kola Peninsula. Moreover, four possible palaeo-ice streams are identified in the region. Mapping individual moraine hummocks, rather than hummocky moraine spreads as in previous mapping attempts, reveals multiple ice margins across the Kola Peninsula. A noteworthy ~25 km wide belt of hummocky moraines aligned north-south across the Kola Peninsula is tentatively attributed to the Younger Dryas (c. 12.8-11.9 ka) ice marginal zone. The so-called “ring-and-ridge” hummock moraines that are predominantly observed within this ice marginal zone suggest down-wasting and stagnant ice margins. The meltwater landform record also reveals subglacial channel networks along the northern coastline that suggest warm-based conditions of the ice sheet may have been induced by warm currents in the Barents Sea during the last glacial-interglacial transition.</p><p>This research will provide crucial empirical data for validating numerical model simulations of the FIS, which in turn will further our understanding of ice sheet dynamics in other Arctic, Antarctic, and Alpine regions.</p>

Quantitative reconstructions of the last glaciation of the Barents Sea: a review of ice-sheet modelling problems

1997 ◽  
Vol 21 (2) ◽  
pp. 200-229 ◽  
Author(s):  
Martin J. Siegert
Keyword(s):  
Barents Sea ◽  
Thickness Distribution ◽  
Ice Sheet ◽  
Complete Coverage ◽  
Last Glaciation ◽  
The Barents Sea ◽  
Late Weichselian ◽  
Quantitative Reconstructions ◽  
The Last Glacial ◽  
Modelling Problems

Reconstructions of the Late Weichselian ice sheet within the Barents Sea have varied from complete coverage of a large (3 km thick) grounded ice mass, to a situation in which glacier extent was restricted to the Svalbard coast. Recently obtained geological data indicate that 1) glaciation of the Barents Sea occurred after 25 000 years ago; 2) the ice sheet was at its maximum extent at around 20 000 years ago; 3) the maximum-sized ice sheet covered the entire Barents Shelf; and 4) ice-sheet decay began at about 16 500 years ago. The ice sheet was, consequently, one of the last to grow and first to decay during the last glacial. However, this recently derived chronology of glacial events has reintroduced problems concerning the thickness distribution of the maximum- sized ice sheet, and the glaciological processes by which rapid glaciation and ice decay happened. In particular, the situation in which regional glaciation of Bjomoya occurred at the same time as grounded ice (and ice-stream activity) within the relatively deep Bjørnøyrenna is yet to be understood fully. This article provides a review of reconstructions of the last Barents ice mass, and compares these models with geological and palaeoceanographic information from the area in order to provide a summary of what is presently known, and to indicate explicitly what is not known, about the Late Weichselian Barents Sea ice sheet.

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