(5) a gasoline -powered electric generator. This non-interference 

 research operation is shown in Figiires llA and IIB. Figure HA shows 

 the tracked vehicle with the recorder/ driver mounted inside its ca- 

 bin, and trailing power cables to the gasoline -powered generator 

 and recorder/driver transducer on the ice. Figure IIB shovs the 

 recorder/ driver transducer coupled to the ice. The snow cover was 

 shoveled away, and the transducer was set in a water filled pot (bor- 

 rowed from the galley) which rested on the ice. 



DISCUSSION OF DATA 



Currents 



The current meter data for all of the seven sites shown in 

 Figure 2 indicates that the currents in the area are predominantly 

 tidal. Tidal ciirrents are the horizontal movements of water that 

 accompany the rise and fall of the tide. The horizontal movement 

 of the tidal current, and the vertical movement of the tide, are in- 

 timately related parts of the same phenomenon induced by the tide- 

 producing forces of the sun and moon. Tidal currents, like the tides, 

 are periodic; it is the periodicity of the tidal current that dis- 

 tinguishes it from other types of currents, which are genera3J.y called 

 non- tidal currents. Non-tidal ciirrents are generated by causes that 

 are independent of the tide, such as winds, fresh water rvin-off, and 

 differences in water density and temperature. Currents of this class 

 do not exhibit the periodicity of tidal currents. 



The tidal currents in a restricted area, such as the study area, 

 are generally of the reversing type; i.e., the current flows in one 

 direction for a period of about six hoijrs, then reverses and flows in 

 the opposite direction for approximately the same period of time. The 

 current flowing towards land is generally referred to as the flood 

 cvirrent, and the current flowing seaward is called the ebb ciirrent. 

 The reversal in ctinrent direction gives rise to a period of slack 

 water during which the speed of the current is zero. An example of 

 these featiires is shown in Figure 12, which denotes a section of the 

 current meter data obtained at 228 meters depth at Site 1. The tidal 

 current in the study area is semi-diurnal; therefore, the current 

 will reverse direction twice daily with two floods and two ebbs. The 

 figvire shows the reversal in current direction, and the change in 

 speed from zero to a maxim^Im dinring each flood and ebb at Site 1. 

 The current floods towards 20° (north-northeasterly) and ebbs to- 

 wards 225° (southwesterly). The shift in direction from ebb to 

 flood is gradual, whereas the shift from flood to ebb is relatively 

 abrupt . 



The strongest currents occur with the spring tides at full and 

 new moon, and the weakest cin-rents with the neap tides during the 

 moon's first and third quarters. The change in strength of the 

 measured tidal current at Site 1 and its relation to the predicted 



324 



