HYDROLOGY OF THE BRANSFIELD STRAIT 39 



in depth at the stations. In future work in the Bransfield Strait and similar areas the 

 number of stations must be greatly increased, particularly on the steeply shelving 

 continental slopes leading to the main channel through the strait. 



If two stations are considered whose depths differ greatly, it cannot be assumed that 

 along the potential surface cutting the bottom at the station of lesser depth the difference 

 of pressure is nil. That is to say the physical characteristics of the water between the 

 stations at depths below that of the shallower station affect the height or topography of 

 the various isobaric surfaces at all points between the stations. Consequently, when 

 determining the difference of height in the sea surface or any other isobaric surface, a 

 method must be employed in which the specific volume of the sea water below the 

 potential surface referred to above is taken into account. Such a method was worked 

 out by Jacobsen and Jensen (1926). These workers, however, assumed a linear variation 

 in the specific volume in both a horizontal and a vertical direction. A glance at the 

 vertical section of density in the Bransfield Strait shows that this is not always correct. 

 When the difference of depth between the stations is great the correction factor C in the 

 Jacobsen and Jensen formula generally becomes great and may be dubious. However, 

 by using this method the main currents in the Bransfield Strait were determined as 

 follows. Water from the Bellingshausen Sea flows in a north-easterly direction at the 

 south-western end of the strait, is diverted by the shelves of the islands of Brabant, Low 

 and Smith, and enters the Bransfield Strait between Smith and Low Islands. Another 

 inflow is in the relatively deep channel between Smith and Snow Islands. This water 

 continues up the strait in a north-easterly direction, after having passed north or south 

 of Deception Island. The north-easterly current along the southern coast of the South 

 Shetland Islands is relatively strong. Part of the water which has passed Deception 

 Island makes a characteristic bend to the south-east and sometimes reaches more than 

 half-way across the strait before it turns again to the north-west to join the current along 

 the South Shetland Islands. At the eastern end of the strait the influence of a current 

 from the Weddell Sea is apparent. Having thus obtained a general idea of the water 

 movements, it was decided to try and find a more exact method for determining the 

 topography of the various surfaces required. 



Professor B. Helland-Hansen, Director of the Geophysical Institute at Bergen, 

 kindly gave me particulars of a method which he and Nansen had previously worked 

 out. A vertical section of the anomaly of specific volume is constructed. At depths 

 greater than 1500 or 2000 m. in an area such as the Bransfield Strait it is seen that the 

 isosteres are horizontal. In this case it may be assumed that the isobaric and isosteric 

 surfaces lie parallel to the level surfaces, and hence there are no acting forces and no 

 convection currents. The depth at which the isosteres become horizontal is then taken 

 as the datum level of zero current for all stations in the section. The isostere at this 

 datum level is then extended horizontally on either side to cut the bottom contour and 

 continue along the line of stations. Above the datum level the isosteres are usually 

 inclined ; they are continued until they cut the bottom contour, and from this point the 

 lines are drawn horizontal. In this way a series of levels and values is obtained which 



