FEATURES OF TERRIGEN1C MATERIAL TRANSPORT BY ICE IN POLAR SEDIMENTATION

Transcription

1 G. A. Tar aso v Murmansk Marine Biological Institute of the Russian Academy of Sciences Robert Spielhagen GEO MOR, Kiel Hannes Grobe Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven Wyprawy Geograficzne na Spitsbergen UMCS, Lublin 1992 FEATURES OF TERRIGEN1C MATERIAL TRANSPORT BY ICE IN POLAR SEDIMENTATION Processes of ice transport of terrigenic sediments and their deposition at the sea bottom, as the result of ice melting are well known, however, there are still numerous unexplained questions concerning the problem. Formation of various lithological types in a sedimenation layer is connected with ice factor. Depending on the depth of the basin, ice density distribution and glacier range, different types of sediments are accumulated. To determine such type of accumulation a term ice-marine" sediments is used, often replaced by the term iceberg" sediments or incorrect term glacier-marine" ones. Obviously, different terms concerning these phenomena are used by different authors. It is particularly confusing when glacier sediments in the regions of the Pleistocen Glaciation are investigated. Hence, description of features of transport of terrigenic deposits by ice, and accompanying processes of deposition of hard mineral particles on the bottom of the basin is so important, particularly if we consider the fact that the role of icepack in the current sedimentation process in polar basins is so significant. The paper presents the results of investigations carried out during the international transpolar expedition on the German icebreaker RV Polarstera" cruise ARK-V111/3 (Fig. 1) from 1 August till 10 October 1991 (Chief Scientist prof. Dieter K. Futterer, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven) and during the expedition of the Murmansk Marine Biological Institute of the Russian Academy of Sciences to the Hornsund Fiord region in Spitsbergen in summer The ice-breaker took the route across the central Arctic through deep Nansen and Amundsen basins, submarine Gakel and Lomonosov ridges. There were young marine ice (one year old), packice (several years old) and icebergs frozen into ice. It is characteristic that Arctic ice cover and icebergs and active glaciers in Spitsbergen contain a significant amount of terrigenic material (Figs. 2-4). There are different ways of deposition of the sedimentation material in ice: silt-sand sediments from the bottom freeze into ice, sometimes also rubbles from shallow 81

2 parts of the sea appear there during tides; weathering products fall down from the slopes on top of tidal ice (?) or river ice which is separated from the ice cover and floats in water; aeolian and atmospheric transport of silt-clay particles onto the ice surface; freezing of sediments floating in water at mouths of Arctic rivers; catching of large parts of material form latteral and basal moraines by ice tongues, etc. Obviously, ice broken at the edge of the sea follows the great transarctic drift and stays there for several years it melts reaching the Greenland Sea. Well visible, dark or dark-grey layers of sand-silt-clay material were observed on edges of ice-floes broken by the ice-breaker. There are places were 5-7 significant layers were visible. As in summer, ice surface becomes very warm, the ice melts gradually and terrigenic material or separate parts of materials are melted out (Fig. 3). Samples collected in the vicinity of the geographical North Pole from the ice surface proved that it was covered by silt-clay particles (Fig. 5). The results of granulometric analysis of the terrigenic material were as follows: fraction mm 2.1/0%*; mm 15.3/0.4%; mm 37.9/18,0%; mm 13.1/7.2%; mm 17.4/16.7%; less than mm 14.1/57.7%. Quartz is the most common in the light fraction (57%), feldspar (24%), plagioclase (4,3%) and schist (4.7%) are in minor amounts. The heavy fraction consists of pyroxene 34.5/15.3%, minerals from the epidot group 20.3/16.4%, black ore minerals 14.7/14.3% common hornblende 6.9/16.9%, garnet 5.4/10.4%, sphene 4.6/4.4%. The results of chemical analysis are presented in the table. Fig. 4 presents terrigenic material transported by a small iceberg in the Hornsund Bay. It shows clearly how the silt-clay mass built of the terrigenic material flows down the iceberg. In such cases, parts of frozen clay, various in size, fall down on to the bottom. Obviously such a process takes place also in the Central Arctic. When the sea depth is larger than 1000 m, the particles clay falling down, are partly dissolved in water and lose their volume. They disappear on the bottom in a muddy cover. Hence, ice cover of the Polar Ocean is responsible for transport of large amounts of terrigenic sedimentary material. Terrigenic material from ice is deposited every year on the sea bottom due to ice melting in spring-summer season and ice breaking in autumn-winter season. The material is in balance, i.e. accumulation and deposition of material are equal. According to certain data the amount of material in the Arctic basin is approximately x9 tons. 50% of this material is deposited on the bottom each year. The processes of accumulation, deposition, transit and equal distribution of the material can be observed in the Arctic basin. Such a picture is typical for the second half of the Holocene. In late and postglacial periods the process of sedimentation was very intensive in Central Arctic. * The results of analysis of material from the bottom, the layer 0-3 cm, are presented (station 2190; North Pole) 82

3 Table 1. Chemical analysis ог sediments from ice surfacc and the upper layer of the bottom, station 2190 (North Pole), % NN Sample CO 2 F e CaO MgO R Al P 0 2 S MnO CaCO (0-3cm) Ice

4 84 Fig. 1. Cruise ARK-VIII/3 PV POLARSTERN"

5 Fig. 2. Terrigenic material in ice in the vicinity of geographical point North Pole. Photo by G. Tarasov. 85

6 Fig. 3. Debris on the surface of the Hans Glacier (Hornsund Fiord). Photo by G. Tarasov Fig. 4. Transport of terrigenic material by an iceberg in Hornsund Fiord (W. Spitsbergen). Photo by G. Tarasov 86

7 Fig. 5. X-ray images of ice samples with lerrigenic material in the vicinity of the geographical point North Pole. Photo by H. Grobe. 87