B . Present Antarctic Marine Sediments 



The chief features that characterize recent Antarctic sedimentation, according 

 to Lisitzyn (1962), are: 



1 . Almost complete absence of runoff. 



2. Little chemical weathering; most water on the continent is In a solid 

 state . 



3. Negligible role of wave erosion; the ice shelves and sea ice, which 

 together surround the continent, effectively dampen wave motion. 



4. Recent volcanic activity . 



5. Little chemical precipitation; the low temperatures of the water inhibit 

 precipitation of CaC03. 



6. Glacial erosion and the seaward movement of glacial ice are the chief 

 factors responsible for the removal of material from land and its subse- 

 quent deposition as marine sediment . 



7. The luxurious growth of phytoplankton, especially near the ice edge; 

 diatoms are the chief source of organic matter In the sediments . 



8. The rugged topography upon which the sediments are accumulating; 

 these sediments are distributed by oceanic currents after they are 

 dropped by floating ice . 



Most of the sedimentary material in Antarctica accumulates away from the 

 coasts in the zone of maximum deposition by icebergs. Consequently, most of 

 the glacial marine sediment falls 100 to 200 miles from shore on the outlying 

 parts of the continental shelf, on the continental slope, and on the continental 

 rise . This is explained by the fact that most of the melting of the icebergs occurs 

 in the warmer waters away from shore. Inshore, where sedimentation is slower, 

 the shelf has a rugged topography, almost bare of sediments (Lisitzyn, 1962) . 



A 7.6-meter core, reported by Hough (1950) to penetrate to sediments of 

 Nebraskan age, was obtained from the continental rise in the Ross Sea. Even If 

 the age of the Nebraskan glacial advance were assumed to be 300,000 years 

 (after Fairbrldge, 1961) rather than 700,000 years (after Hough, 1950) deposition 

 of 8.0 meters (correcting for 5% compaction by the coring device) would give an 

 average sedimentation rate of only 2 .7 centimeters per thousand years . This rep- 

 resents, by extrapolation, only 90 feet of sediment during the entire Pleistocene 

 epoch In this zone of maximal sedimentation seaward of the continental shelf. 



According to Evteev (1959), the average annual rate of bedrock erosion by 

 the ice cap Is nearly the same as that by rivers on temperate continents. 



12 



