scholarly journals Seabed topography beneath Larsen C Ice Shelf from seismic soundings

2013 ◽  
Vol 7 (4) ◽  
pp. 4177-4206
Author(s):  
A. M. Brisbourne ◽  
A. M. Smith ◽  
E. C. King ◽  
K. W. Nicholls ◽  
P. R. Holland ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Ocean Circulation ◽  
Seismic Velocity ◽  
Gravity Data ◽  
Gravity Inversion ◽  
Oceanic Circulation ◽  
Ice Shelf ◽  
Free Air ◽  
Cavity Thickness ◽  
Free Air Gravity

Abstract. Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines were collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-shelf oceanic circulation may be affected by ice draft and sub-shelf cavity thickness. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general <10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-shelf ocean circulation models.

scholarly journals Seabed topography beneath Larsen C Ice Shelf from seismic soundings

2014 ◽  
Vol 8 (1) ◽  
pp. 1-13 ◽  
Author(s):  
A. M. Brisbourne ◽  
A. M. Smith ◽  
E. C. King ◽  
K. W. Nicholls ◽  
P. R. Holland ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Ocean Circulation ◽  
Seismic Velocity ◽  
Gravity Data ◽  
Gravity Inversion ◽  
Seismic Velocities ◽  
Oceanic Circulation ◽  
Ice Shelf ◽  
Free Air ◽  
Free Air Gravity

Abstract. Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-ice shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines was collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-ice shelf oceanic circulation may be affected by ice draft and seabed depth. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general < 10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-ice shelf ocean circulation models.

scholarly journals Inversion of IceBridge gravity data for continental shelf bathymetry beneath the Larsen Ice Shelf, Antarctica

2012 ◽  
Vol 58 (209) ◽  
pp. 540-552 ◽  
Author(s):  
James R. Cochran ◽  
Robin E. Bell
Keyword(s):  
Continental Shelf ◽  
Ocean Circulation ◽  
Gravity Data ◽  
Radar Data ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Free Air ◽  
Free Air Gravity ◽  
Larsen Ice Shelf ◽  
Possible Cause

AbstractA possible cause for accelerated thinning and break-up of floating marine ice shelves is warming of the water in the cavity below the ice shelf. Accurate bathymetry beneath large ice shelves is crucial for developing models of the ocean circulation in the sub-ice cavities. A grid of free-air gravity data over the floating Larsen C ice shelf collected during the IceBridge 2009 Antarctic campaign was utilized to develop the first bathymetry model of the underlying continental shelf. Independent control on the continental shelf geologic structures from marine surveys was used to constrain the inversion. Depths on the continental shelf beneath the ice shelf estimated from the inversion generally range from about 350 to 650 m, but vary from <300 to >1000 m. Localized overdeepenings, 20-30 km long and 900-1000 m deep, are located in inlets just seaward of the grounding line. Submarine valleys extending seaward from the overdeepenings coalesce into two broad troughs that extend to the seaward limit of the ice shelf and appear to extend to the edge of the continental shelf. The troughs are generally at a depth of 550-700 m although the southernmost mapped trough deepens to over 1000 m near the edge of the ice shelf just south of 68° S. The combination of the newly determined bathymetry with published ice-draft determinations based on laser altimetry and radar data defines the geometry of the water-filled cavity. These newly imaged troughs provide a conduit for water to traverse the continental shelf and interact with the overlying Larsen C ice shelf and the grounding lines of the outlet glaciers.

Modelling the ocean circulation and the basal melting in the Prydz Bay-Amery Ice Shelf system

2021 ◽  
Author(s):  
Jing Jin ◽  
Antony J. Payne ◽  
William Seviour ◽  
Christopher Bull
Keyword(s):  
Heat Transport ◽  
Ocean Circulation ◽  
Water Masses ◽  
Prydz Bay ◽  
Effect Of Temperature ◽  
Oceanic Circulation ◽  
Ice Shelf ◽  
Thermodynamic Structure ◽  
Amery Ice Shelf ◽  
Basal Melting

&lt;p&gt;The basal melting of the Amery Ice Shelf (AIS) in East Antarctica and its connections with the oceanic circulation are investigated by a regional ocean model. The simulated estimations of net melt rate over AIS from 1976 to 2005 vary from 1 to 2 m/yr depending primarily due to inflow of modified Circumpolar Deep Water (mCDW). Prydz Bay Eastern Costal Current (PBECC) and the eastern branch of Prydz Bay Gyre (PBG) are identified as two main mCDW intrusion pathways. The oceanic heat transport from both PBECC and PBG has significant seasonal variability, which is associated with the Antarctic Slope Current. The onshore heat transport has a long-lasting effect on basal melting. The basal melting is primarily driven by the inflowing water masses though a positive feedback mechanism. The intruding warm water masses destabilize the thermodynamic structure in the sub-ice shelf cavity therefore enhancing the overturning circulations, leading to further melting due to increasing heat transport. However, the inflowing saltier water masses due to sea-ice formation could offset the effect of temperature through stratifying the thermodynamic structure, then suppressing the overturning circulation and reducing the basal melting.&lt;/p&gt;

Sea floor topography modeling by cumulating different types of gravity information

2020 ◽  
Author(s):  
Lucia Seoane ◽  
Benjamin Beirens ◽  
Guillaume Ramillien
Keyword(s):  
New England ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Extended Kalman Filtering ◽  
Sea Floor ◽  
Single Beam ◽  
Free Air ◽  
Free Air Gravity ◽  
Great Meteor Seamount

&lt;p&gt;We propose to cumulate complementary gravity data, i.e. geoid height and (radial) free-air gravity anomalies, to evaluate the 3-D shape of the sea floor more precisely. For this purpose, an Extended Kalman Filtering (EKF) scheme has been developed to construct the topographic solution by injecting gravity information progressively. The main advantage of this sequential cumulation of data is the reduction of the dimensions of the inverse problem. Non linear Newtonian operators have been re-evaluated from their original forms and elastic compensation of the topography is also taken into account. The efficiency of the method is proved by inversion of simulated gravity observations to converge to a stable topographic solution with an accuracy of only a few meters. Real geoid and gravity data are also inverted to estimate bathymetry around the New England and Great Meteor seamount chains. Error analysis consists of comparing our topographic solutions to accurate single beam ship tracks for validation.&lt;/p&gt;

The unification of gravity data for Ireland-Northern Ireland

2020 ◽  
Vol 39 (2) ◽  
pp. 135-143
Author(s):  
Sajjad Sajjadi ◽  
Zdeněk Martinec ◽  
Patrick Prendergast ◽  
Jan Hagedoorn ◽  
Libor Šachl ◽  
...  
Keyword(s):  
Northern Ireland ◽  
Tide Gauge ◽  
Gravity Data ◽  
Base Station ◽  
Base Stations ◽  
Data Format ◽  
Free Air ◽  
Vertical Datum ◽  
Systematic Biases ◽  
Free Air Gravity

The systematic biases and errors associated with gravity data in Ireland and Northern Ireland and the conversion of gravity to a consistent and unified system are analyzed. The gravity data in Ireland and Northern Ireland are given in different coordinate systems (Irish Grid and Irish Transverse Mercator), different gravity base stations (Dunsink and Cambridge), and different vertical datums (Malin Head and Belfast tide gauge). The conversion of the gravity data to a consistent system, which refers to unified coordinates, base station, and vertical datum, is essential in geophysics and geodesy, especially in geoid determination. A new standardized and unified data format is computed and proposed for the supply of gravity data for Ireland and Northern Ireland to minimize the potential of misinterpreting the data. As part of this study, simple Bouguer and free-air gravity anomaly maps are produced for Ireland and Northern Ireland to give an example of how to integrate the data.

The Origin of Lunar Mascon Basins

Science ◽  
2013 ◽  
Vol 340 (6140) ◽  
pp. 1552-1555 ◽  
Author(s):  
H. J. Melosh ◽  
Andrew M. Freed ◽  
Brandon C. Johnson ◽  
David M. Blair ◽  
Jeffrey C. Andrews-Hanna ◽  
...  
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Element Model ◽  
Isostatic Adjustment ◽  
Melt Pool ◽  
Free Air ◽  
Free Air Gravity ◽  
Bull's Eye ◽  
Gravity Recovery ◽  
The Impact

High-resolution gravity data from the Gravity Recovery and Interior Laboratory spacecraft have clarified the origin of lunar mass concentrations (mascons). Free-air gravity anomalies over lunar impact basins display bull’s-eye patterns consisting of a central positive (mascon) anomaly, a surrounding negative collar, and a positive outer annulus. We show that this pattern results from impact basin excavation and collapse followed by isostatic adjustment and cooling and contraction of a voluminous melt pool. We used a hydrocode to simulate the impact and a self-consistent finite-element model to simulate the subsequent viscoelastic relaxation and cooling. The primary parameters controlling the modeled gravity signatures of mascon basins are the impactor energy, the lunar thermal gradient at the time of impact, the crustal thickness, and the extent of volcanic fill.

scholarly journals The Regime of the Western Part of the Ross Ice Shelf Drainage System

1966 ◽  
Vol 6 (43) ◽  
pp. 55-68 ◽  
Author(s):  
M. Giovinetto ◽  
Edwin S. Robinson ◽  
C. W. M. Swithinbank
Keyword(s):  
Cross Sections ◽  
Drainage System ◽  
Gravity Anomalies ◽  
Ice Shelf ◽  
Glacier Surface ◽  
Ross Ice Shelf ◽  
Movement Data ◽  
Free Air ◽  
The Difference ◽  
Free Air Gravity

AbstractThe net mass budget is estimated for the western part of the Ross Ice Shelf drainage system. The area of the system is (1.75±0.26) × 106 km.2, and the drainage periphery extends along the eastern flank of the Trans-Antarctic Mountains between lat. 77° 58′ S., long. 164° 37′ E. and lat. 85° 27′ S., long. 147°50′ discharge is estimated from vertical cross-sections and corresponding ice-movement data for eight outlet glaciers. Free-air gravity anomalies, corrected for the effect of terrain above the glacier surface, are used to determine cross-sections of valleys by comparison with theoretical gravity profiles for several two-dimensional valley models. These data provide a basis for estimating the rate of ice discharge from the plateau, which is compared with the estimated rate of net accumulation at the surface, to determine the net budget of the ice sheet in the region. Representative mean rates of ice discharge measured in different types of glaciers are approximately 0.25 × 1015 g. km.−1 yr.−1 in outlet glaciers with large basins, and 0.05 × 1015 g. km.−1 yr.−1 in outlet glaciers with small basins. Taking into account the snowshcd area and the rate of accumulation, the rate of ice discharge in cirque and piedmont glaciers is estimated at about 0.02 × 1015 g. km.−1 yr.−1 The difference ((48±29) × 1015 g. yr.−1) between mass input ((96±25) × 1015 g. yr.−1) and mass output ((48±15) × 1015 g. yr.−1) is large enough relative to the estimated standard error to indicate a probable positive net budget.

scholarly journals Usporedba različitih pristupa Bouguer-ove redukcije na temelju satelitskih gravimetrijskih podataka

Geofizika ◽  
2020 ◽  
Vol 37 (2) ◽  
pp. 237-261
Author(s):  
Fan Luo ◽  
Xin Tao ◽  
Guangming Fu ◽  
Chong Zhang ◽  
Kun Zhang ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Gravitational Effect ◽  
Seismic Profile ◽  
Bouguer Gravity ◽  
Seismic Profiles ◽  
Satellite Gravity ◽  
Free Air ◽  
Free Air Gravity

Satellite gravity data are widely used in the field of geophysics to study deep structures at the regional and global scales. These data comprise free-air gravity anomaly data, which usually need to be corrected to a Bouguer gravity anomaly for practical application. Bouguer reduction approaches can be divided into two methods based on the coordinate system: the spherical coordinates method (SBG) and the Cartesian coordinates method; the latter is further divided into the CEBG and CBG methods, which do and do not include the Earth’s curvature correction. In this paper, free-air gravity anomaly data from the eastern Tibetan Plateau and its adjacent areas were used as the basic data to compare the CBG, CEBG, and SBG Bouguer gravity correction methods. The comparison of these three Bouguer gravity correction methods shows that the effect of the Earth’s curvature on the gravitational effect increases with increasing elevation in the study area. We want to understand the inversion accuracy for the data obtained by different Bouguer gravity reduction approaches. The depth distributions of the Moho were obtained by the interface inversion of the Bouguer gravity anomalies obtained by the CBG, CEBG, and SBG, and active seismic profiles were used as references for comparison and evaluation. The results show that the depths of the Moho obtained by the SBG inversion are more consistent with the measured seismic profile depths. Therefore, the SBG method is recommended as the most realistic approach in the process of global or regional research employing gravity data.

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