Current Measurements

Water current measurements were made this season at the 100 m site of most of our coastal transects using a newly purchased InterOcean S4 electromagnetic current meter. This current meter is housed in a 250 mm diameter sphere, has no moving parts, records data internally and is ideal for deployment through our 300 mm diameter access holes in the sea ice. The instrument was programmed and interrogated with an IBM PC operated in the warm environment of the wannigan (NZ-1).

Two modes of deployment were used at the 100 m deep sites. Water column profiling measurements were made while either raising or lowering the current meter with our new hydraulically controlled hydrographic winch. Short term (12-24 hours) fixed-mooring measurements were also made by suspending the current meter on the winch wire 1.5 m ± 0.5 m above the sea floor. The height of the instrument above the sea floor could not be fixed precisely using this method of deployment because of the approximately 1 m tidal rise and fall of the sea ice platform.

Profiles and short term deployments were also made in central Granite Harbour near the MacKay Glacier Tongue and in central New Harbour (S216 Trap Site). This data will be used for planning a longer term deployment (2 months) proposed for the 1988-1989 season.

Examples of results from profiles and stationary moorings are presented in Figures 3 and 4. The highest speed measured along the southwestern Ross Sea coast page 9

Figure 3. Current measurements at Gregory Island (98 m site).

A.	Profile showing consistent speed and direction through most of the water column.
B.	Stationary mooring 1-2 m above the sea floor (13 hour 48 min record). Note the increase in speed as high tide is approached and progressive change in direction from southward flow to a northward flow. The strongest flow is to the north.

page 10

Figure 4. Current measurements at Cape Armitage (90 m site).

A.	26 hour deployment 1-2 m above the sea floor showing currents up to 75 cm/sec were recorded flowing to 150° true (SSE). Lower velocity currents up to 25 cm/sec flowing to 250° true (WSW).
B.	Profile about 2 hours after the end of record above (A). A steady flow of 75 cm/sec to 150° T is shown for most of the water column.

page 11 was 25 to 30 cm/sec at Gregory Island (Figure 3). The lowest current speed along this coast was 12 cm/sec, measured at Blue Glacier. Current directions are parallel to the coast and change by 180° during the tidal cycle. Speeds measured in embayed areas such as New Harbour, Granite Harbour and Tripp Bay are lower (less than 12 cm/sec) than those on the exposed coast. Current direction at Cape Armitage (Figure 4) also changes with the tidal period, with speeds up to 75 cm/sec, and were the highest measured this season.