The westernmost stations contained the largest percentages of Shelf 

 Water, Two stations taken in 1964, Nos. 61 and 62, were completely 

 Shelf Water from the surface to the bottom. These two stations, occupied 

 on 1 March, were taken after the seasonal reversal which occurs in mid- 

 February. Stations occupied in other years, at the same location, pro- 

 duced different results, indicating year to year variations. 



Generally, during the summer season, Shelf Water is found below 250 

 meters (820 feet)» west of 174°E (Fig. 19). This water layer deepens and 

 decreases in thickness eastward, until by 175°W it is found below 470 

 meters (1,542 feet) and then only at the southernmost stations. North 

 of 73°30'S the Shelf Water mass was not observed except close to the 

 Victoria Land coast. Shelf Water is encountered deeper in the water 

 column along the Ross Ice Shelf and the northern coast of Ross Island. 



A broad mass of Shelf Water extends from the southwest area parallel- 

 ing the ice shelf. This water appeared to move toward the northeast at 

 177°E. The Shelf Water was observed to become deeper as it traveled 

 further north and east. The water mass also extends eastward from Lady 

 Newnes Ice Shelf (Fig. 19). It was observed deeper toward the east, being 

 at 82 meters (269 feet) at station 47, 100 meters (32 8 feet) at station 

 46, and at 168 meters (551 feet) at station 45. 



Due to Pennell Bank acting as a barrier, Shelf Water must flow either 

 north or east out of the Ross Sea. A small amount flows eastward, south 

 of this barrier, but the major portion of the Shelf Water is believed to 

 flow northward between Pennell Bank and Victoria Land. Two troughs (Fig. 3) 

 separated by a broad ridge, parallel the coast from the southwestern corner 

 to the continental slope. These troughs form a natural path for the out- 

 flow of Shelf Water. 



An interesting feature is the high mound of Shelf Water centered at 

 station 19 (Fig. 8). Those stations nearest station 19 show Shelf Water 

 only below 200 meters (656 feet), while at station 19, Shelf Water was 

 found 37 meters (121 feet) below the surface. The causes of this are un- 

 known. The dynamic topography indicates a strong gyral encircling station 

 19, but the shallow reference level (200 decibars) causes the isobars to 

 follow the 2 8.00 sigma-t contours. The use of the isobars as streamlines 

 is somewhat doubtful. This position was reoccupied 26 days later with 

 no mounding observed, Shelf Water being found at 325 meters (1066 feet), 

 a change in depth of 288 meters (945 feet). This significant change in 

 depth suggests that Shelf Water is flowing laterally from station 19. 

 Other reoccupied stations (e.g. stations 18 and 100) show a similar verti- 

 cal temperature fluctuation. 



The bottom water in the southeastern Ross Sea over the continental 

 shelf^ has characteristics very similar to Shelf Water, but differs by 

 having somewhat lower salinity and sigma-t values; therefore, it is not 

 classified as Shelf Water. Its temperatures are near the freezing point 



28 



