Abstracts
Paläozeanographische
Modellierung
Fachbereich Geowissenschaften
Universität Bremen
back to
Klaus Grosfeld
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Berichte zur Polarforschung, 130, 148pp. 1993.
(Printed version of Ph.D. thesis submitted to the Faculty of Science,
Westfälischen Wilhelms-Universität Münster,
Germany)
Investigations on temperature regime and mass balance
of the Filchner-Ronne Ice Shelf, Antarctica, with special
interest regarding melting and freezing processes
(Untersuchungen zu Temperaturregime und Massenbilanz
des Filchner-Ronne Schelfeises, Antarktis, unter besonderer
Berücksichtigung von Anfrier- und Abschmelzprozessen)
K. Grosfeld
Institut für Geophysik, Forschungsstelle für physikalische Glaziologie
der Westfälischen Wilhelms-Universität Münster,
Germany
This thesis mainly addresses to the temperature-depth profile and the mass balance of ice shelves, especially the Filchner-Ronne Ice Shelf in Antarctica. Ice shelves represent the main drainage basins of the Antarctic Ice Cap and are sensitive indicators for climate induced mass-balance changes of Antarctica. In addition, the central part of Filchner-Ronne Ice Shelf consists of meteoric and a layer of marine ice with thicknesses up to 400 m, which accumulates from the ocean underneath the ice shelf by crystallization processes. This layer contributes to the mass budget of the ice shelf and influences the temperature regime significantly. Thus, ice/ocean interaction plays an important role in the dynamics of the Filchner-Ronne Ice Shelf.
During the German Antarctic field season 1989/90 (ANT VIII/5) special interest was focussed on the examination of the temperature-depth profile, the ice thickness and the bottom melting by means of hot-water drillings. The drillholes were located at 77oS and 52.3oW, about 30 km inland from the ice front. The installation of temperature chains inside drillholes down to the sea water underneath the ice shelf yield data about the temperature-depth profile, the ice thickness and its variation, and the sea-water temperature. In addition, TDR-measurements on sensor lines and surface measurements for the determination of ice-shelf bottom melting were performed. From re-measuremets in 1991/92 a value for the bottom melting rate of m=-1.4+/-0.5 m/yr could be determined from three independent measuring techniques.
On the base of heat conduction theory a two-dimensional thermal ice-shelf model was developed, regarding thermal properties that depend on temperature and salinity to simulate the influence of the freezing process of basal marine ice on the temperature profile. The time dependend calculation was done by means of FD-methods with normalized depth and time coordinates. Boundary values were taken from geophysical, geodetic, glaciological and oceanographic data and models of the Filchner-Ronne Ice Shelf region. The model results show a strong influence of basal accretion on the temperature field in the central part. Basal freezing and melting rates were found under consideration of mass conservation along flowlines. The calculation of this mass balance parameters allows for a separation of the ice shelf in a freezing, an intermediate, and a melting regime. In the area of maximum freezing rates the simulation shows temperature-depth profiles with nearly isothermal conditions in the marine layer. Near the ice edge melting occurs which erodes the relatively warm basal layer, whereas heat conduction processes dominate the intermediate regime, where neither significant freezing nor melting occurs. A comparison of measured and calculated temperature-depth data along flowlines shows convincing results.
The temperature regime of the ice shelf has a strong influence on the material properties of ice. Examples using the results of the simulation are shown for the flow parameter with regard to dynamic modelling and for the absorption of electo-magnetic waves used for radio-echo soundings.
[Link to AWI]
