New determinations of tides on the north-western Ross Ice Shelf

2020 ◽  
pp. 1-14
Author(s):  
Richard D. Ray ◽  
Kristine M. Larson ◽  
Bruce J. Haines
Keyword(s):  
Time Series ◽  
Tide Gauge ◽  
High Rate ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Global Positioning ◽  
North Western

Abstract New determinations of ocean tides are extracted from high-rate Global Positioning System (GPS) solutions at nine stations sitting on the Ross Ice Shelf. Five are multi-year time series. Three older time series are only 2–3 weeks long. These are not ideal, but they are still useful because they provide the only in situ tide observations in that sector of the ice shelf. The long tide-gauge observations from Scott Base and Cape Roberts are also reanalysed. They allow determination of some previously neglected tidal phenomena in this region, such as third-degree tides, and they provide context for analysis of the shorter datasets. The semidiurnal tides are small at all sites, yet M2 undergoes a clear seasonal cycle, which was first noted by Sir George Darwin while studying measurements from the Discovery expedition. Darwin saw a much larger modulation than we observe, and we consider possible explanations - instrumental or climatic - for this difference.

scholarly journals A Reconsideration of the Mass Balance of a Portion of the Ross Ice Shelf, Antarctica

1984 ◽  
Vol 30 (106) ◽  
pp. 381-384 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Small Region ◽  
Volume Element ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Velocity ◽  
Flow Band ◽  
Input Gate ◽  
North Western

AbstractThe identification of a small region of grounded ice in the north-western sector of the Ross Ice Shelf has forced a re-evaluation of the mass-balance calculations carried out by Thomas and Bentley (1978). Those authors concluded that the Ross Ice Shelf up-stream of Crary Ice Rise was thickening, but they did not take into account the effects on the velocity field of grounded ice (of which they were unaware), which is located near the input gate to their volume element. Reasonable estimates of the degree to which the ice velocity just up-stream of the grounded ice is diminished indicate that it is no longer possible to conclude that the ice shelf is thickening using Thomas and Bentley’s original flow band. Therefore, a new flow band was chosen which was grid east of Thomas and Bentley’s band and unaffected by any nearby grounded areas. The mass balance in this flow band was found to be zero within experimental error; a difference exceeding about 0.2 m a−1 in magnitude between the thickening and bottom freeze-on rates is unlikely.

scholarly journals A Reconsideration of the Mass Balance of a Portion of the Ross Ice Shelf, Antarctica

1984 ◽  
Vol 30 (106) ◽  
pp. 381-384 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Small Region ◽  
Volume Element ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Velocity ◽  
Flow Band ◽  
Input Gate ◽  
North Western

AbstractThe identification of a small region of grounded ice in the north-western sector of the Ross Ice Shelf has forced a re-evaluation of the mass-balance calculations carried out by Thomas and Bentley (1978). Those authors concluded that the Ross Ice Shelf up-stream of Crary Ice Rise was thickening, but they did not take into account the effects on the velocity field of grounded ice (of which they were unaware), which is located near the input gate to their volume element. Reasonable estimates of the degree to which the ice velocity just up-stream of the grounded ice is diminished indicate that it is no longer possible to conclude that the ice shelf is thickening using Thomas and Bentley’s original flow band. Therefore, a new flow band was chosen which was grid east of Thomas and Bentley’s band and unaffected by any nearby grounded areas. The mass balance in this flow band was found to be zero within experimental error; a difference exceeding about 0.2 m a−1in magnitude between the thickening and bottom freeze-on rates is unlikely.

scholarly journals Ships and their timber source as indicators of connections between regions

AmS-Skrifter ◽  
2020 ◽  
pp. 133-143
Author(s):  
Aoife Daly
Keyword(s):  
Western Europe ◽  
The Baltic Sea ◽  
The North ◽  
Baltic Coast ◽  
Art Objects ◽  
The North Sea ◽  
The Baltic ◽  
North And South ◽  
North Western

The precise dating and determination of the source of timbers in shipwrecks found around the coasts of the North Sea and the Baltic Sea, through dendrochronology allows us to see connections between north and  south, east and west throughout the region and to a high chronological precision. In this paper we take a look at results of recent analyses of timber from ships, and timber and barrel cargoes, to try to draw a chronological picture, from the twelfth to seventeenth centuries, of links between regions, through transport in oak ships and trade of timber. Archaeological finds of oak from timber cargos in shipwrecks and fine art objects (painted panels and sculpture) show the extent to which timber was shipped from Hanseatic towns along the southern Baltic coast, to western and north-western Europe.

scholarly journals Geodetic Results of the Ross Ice Shelf Survey Expeditions, 1962–63 and 1965–66

1969 ◽  
Vol 8 (52) ◽  
pp. 67-90 ◽  
Author(s):  
Egon Dorrer ◽  
Walther Hofmann ◽  
Wilfried Seufert
Keyword(s):  
Maximum Velocity ◽  
Careful Study ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
The North ◽  
Parallel Movement ◽  
Time Reduction ◽  
Observation Method ◽  
East West

By means of modern geodetic observation techniques the ice movement along an east-west and a north-south profile across the Ross Ice Shelf, Antarctica, was measured during the two Antarctic summers, 1962–63 and 1965–66. 103 markers were placed on the 910 km long traverse. Distances were measured by tellurometer, and traverse angles by a precision theodolite between all consecutive markers, normally 8 to 9 km apart. For this type of observation method, six men distributed into three groups of two men each were necessary.The main part of the paper deals with data processing and with the computation of the ice movement. As the ice moves, the geometrical configuration of the traverse changes during the epoch of observation. For this “reduction to epoch” problem two methods are described in detail: (1) time reduction of observations, and (2) time reduction of positions. Between the two field journeys, only linear ice movement can be assumed. It is possible, however, to determine acceleration and curvature of the ice flow at all traverse points where the traverse angles differ considerably from 180°.The result of all computations is the field of velocity vectors along the traverse. Obvious characteristics are the rapid increase of velocity between the McMurdo Ice Shelf and Ross Ice Shelf, the uniform and nearly parallel movement in the middle of the ice shelf (maximum velocity 935 m year−1), the decrease of velocity along the north-south profile, and the systematic increase of divergence of the flow lines towards the ice margins. Careful study of the velocity vector field shows some deviations from an entirely uniform distribution.

Modelling the ocean circulation beneath the Ross Ice Shelf

2003 ◽  
Vol 15 (1) ◽  
pp. 13-23 ◽  
Author(s):  
DAVID M. HOLLAND ◽  
STANLEY S. JACOBS ◽  
ADRIAN JENKINS
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Ross Sea ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Shelf Water ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Shelf Water

We applied a modified version of the Miami isopycnic coordinate ocean general circulation model (MICOM) to the ocean cavity beneath the Ross Ice Shelf to investigate the circulation of ocean waters in the sub-ice shelf cavity, along with the melting and freezing regimes at the base of the ice shelf. Model passive tracers are utilized to highlight the pathways of waters entering and exiting the cavity, and output is compared with data taken in the cavity and along the ice shelf front. High Salinity Shelf Water on the western Ross Sea continental shelf flows into the cavity along the sea floor and is transformed into Ice Shelf Water upon contact with the ice shelf base. Ice Shelf Water flows out of the cavity mainly around 180°, but also further east and on the western side of McMurdo Sound, as observed. Active ventilation of the region near the ice shelf front is forced by seasonal variations in the density structure of the water column to the north, driving rapid melting. Circulation in the more isolated interior is weaker, leading to melting at deeper ice and refreezing beneath shallower ice. Net melting over the whole ice shelf base is lower than other estimates, but is likely to increase as additional forcings are added to the model.

scholarly journals Comparison of in situ time-series of temperature with gridded sea surface temperature datasets in the North Atlantic

2009 ◽  
Vol 66 (7) ◽  
pp. 1467-1479 ◽  
Author(s):  
Sarah L. Hughes ◽  
N. Penny Holliday ◽  
Eugene Colbourne ◽  
Vladimir Ozhigin ◽  
Hedinn Valdimarsson ◽  
...  
Keyword(s):  
Time Series ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Sea Surface ◽  
The North ◽  
Spatial Coverage ◽  
The North Atlantic

Abstract Hughes, S. L., Holliday, N. P., Colbourne, E., Ozhigin, V., Valdimarsson, H., Østerhus, S., and Wiltshire, K. 2009. Comparison of in situ time-series of temperature with gridded sea surface temperature datasets in the North Atlantic. – ICES Journal of Marine Science, 66: 1467–1479. Analysis of the effects of climate variability and climate change on the marine ecosystem is difficult in regions where long-term observations of ocean temperature are sparse or unavailable. Gridded sea surface temperature (SST) products, based on a combination of satellite and in situ observations, can be used to examine variability and long-term trends because they provide better spatial coverage than the limited sets of long in situ time-series. SST data from three gridded products (Reynolds/NCEP OISST.v2., Reynolds ERSST.v3, and the Hadley Centre HadISST1) are compared with long time-series of in situ measurements from ICES standard sections in the North Atlantic and Nordic Seas. The variability and trends derived from the two data sources are examined, and the usefulness of the products as a proxy for subsurface conditions is discussed.

Evolution of supercooling under coastal Antarctic sea ice during winter

2011 ◽  
Vol 23 (4) ◽  
pp. 399-409 ◽  
Author(s):  
Gregory H. Leonard ◽  
Patricia J. Langhorne ◽  
Michael J.M. Williams ◽  
Ross Vennell ◽  
Craig R. Purdie ◽  
...  
Keyword(s):  
Sea Ice ◽  
Freezing Point ◽  
Circulation Pattern ◽  
Late Winter ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
The North ◽  
Antarctic Sea Ice ◽  
Ice Production

AbstractHere we describe the evolution through winter of a layer of in situ supercooled water beneath the sea ice at a site close to the McMurdo Ice Shelf. From early winter (May), the temperature of the upper water column was below its surface freezing point, implying contact with an ice shelf at depth. By late winter the supercooled layer was c. 40 m deep with a maximum supercooling of c. 25 mK located 1–2 m below the sea ice-water interface. Transitory in situ supercooling events were also observed, one lasting c. 17 hours and reaching a depth of 70 m. In spite of these very low temperatures the isotopic composition of the water was relatively heavy, suggesting little glacial melt. Further, the water's temperature-salinity signature indicates contributions to water mass properties from High Salinity Shelf Water produced in areas of high sea ice production to the north of McMurdo Sound. Our measurements imply the existence of a heat sink beneath the supercooled layer that extracts heat from the ocean to thicken and cool this layer and contributes to the thickness of the sea ice cover. This sink is linked to the circulation pattern of the McMurdo Sound.

scholarly journals Towards Reliable Velocities of Permanent GNSS Stations

2016 ◽  
Vol 100 (1) ◽  
pp. 17-26
Author(s):  
Janusz Bogusz ◽  
Anna Klos ◽  
Marta Gruszczynska ◽  
Maciej Gruszczynski
Keyword(s):  
Time Series ◽  
Singular Spectrum Analysis ◽  
Principal Component ◽  
North East ◽  
Temporal Correlations ◽  
The North ◽  
Spatio Temporal ◽  
Permanent Station

Abstract In the modern geodesy the role of the permanent station is growing constantly. The proper treatment of the time series from such station lead to the determination of the reliable velocities. In this paper we focused on some pre-analysis as well as analysis issues, which have to be performed upon the time series of the North, East and Up components and showed the best, in our opinion, methods of determination of periodicities (by means of Singular Spectrum Analysis) and spatio-temporal correlations (Principal Component Analysis), that still exist in the time series despite modelling. Finally, the velocities of the selected European permanent stations with the associated errors determined following power-law assumption in the stochastic part is presented.

scholarly journals GPS determination of the velocity and strain-rate fields on Schirmacher Glacier, central Dronning Maud Land, Antarctica

2007 ◽  
Vol 53 (183) ◽  
pp. 558-564 ◽  
Author(s):  
P.S. Sunil ◽  
C.D. Reddy ◽  
M. Ponraj ◽  
Ajay Dhar ◽  
D. Jayapaul
Keyword(s):  
Strain Rate ◽  
Austral Summer ◽  
Base Station ◽  
Spatially Correlated ◽  
The North ◽  
Schirmacher Oasis ◽  
Global Positioning ◽  
Dronning Maud Land ◽  
Insight Into

Global positioning system (GPS) campaigns were conducted during the 2003 and 2004 austral summer seasons to obtain insight into the velocity and strain-rate distribution on Schirmacher Glacier, central Dronning Maud Land, East Antarctica. GPS data were collected at 21 sites and analyzed to estimate the site coordinates, baselines and velocities. The short-term precision of the base station, MAIT, is estimated from the daily coordinate repeatability solutions during the two years. All GPS points on the glacier were constrained with respect to MAIT and nearby International GPS Service stations. Horizontal velocities of the glacier sites lie between 1.89 ± 0.01 and 10.88 ± 0.01 ma−1 to the north-northeast, with an average velocity of 6.21 ± 0.01 m a−1. The principal strain rates provide a quantitative measurement of extension rates, which range from (0.11 ± 0.01) × 10−3 to (1.48 ± 0.85) × 10−3a−1, and shortening rates, which range from (0.04 ± 0.02) × 10−3 to (0.96 ± 0.16) × 10−3a−1. The velocity and strain-rate distributions across the GPS network in Schirmacher Glacier are spatially correlated with topography, subsurface undulations, fracture zones/crevasses and the partial blockage of the flow by nunataks and the Schirmacher Oasis.

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