General

A geothermal heat-flow probe for in situ measurements of both temperature gradient and thermal conductivity in sediments has recently been designed by D.A. Christoffel and I.M. Calhaem of the Physics Department, V.U.W. The aim of the expedition was to test this equipment at depths of up to 2,000 feet, and to obtain geo thermal heat-flow readings in McMurdo Sound, Antarctica. (Good results have already been obtained by Christoffel and Calhaem, using similar equipment, in Wellington Harbour). Normally such measurements are taken from a ship, but in McMurdo Sound the relatively thin (about 8 feet thick) sea-ice provides an ideal platform from which to work. To simplify the experimental work all of the equipment has been designed to pass through a 4 inch diameter sipri hole, which takes about three quarters of an hour to drill through ice of this thickness.

To obtain a heat-flow reading, at least three feet of sediment is required on the ocean bottom. The heat-flow probe is six feet long, and contains a 150 cm long thermocouple thermometer, which for good results must be embedded in the sediment for at least half of its length.

In a virtually unmapped area like McMurdo Sound, the only way to find mud is by trial and error. I used a piston-corer capable of obtaining a six foot long cylindrical core sample of the sediment. Its operation is quite simple. It is lowered on the end of a steel cable until it is about 20 feet from the bottom. Then it is released automatically from the cable and free-falls the rest of the way. Its momentum is sufficient to drive it into the sediment. It is then retrieved by means of a 20 foot long recovery loop which still connects it to the steel cable.

It will penetrate anything softer than solid rock, so if no core at all is brought up it can safely be assumed that the ocean bottom at that point is rocky. If, however, sufficient sediment is found, the procedure is as follows: page 19

(1)	A temperature profile of the ocean is taken. This is purely a precautionary measure, as large temperature variations with depth can result in an abnormal heat-flow. (in fact the water temperature was very nearly constant at all depths at -3.6°C).
(2)	The heat-flow reading itself is taken. The heat-flow probe is driven into the sediment in the same way as the corer. (The only difference being the electrical cables from the probe to the surface instruments).

First a temperature gradient measurement is taken, and then a thermal conductivity measurement. The heat-flow can be calculated from these by a law analogous to Ohms law. For confirmation of the thermal conductivity readings the core samples are brought back to the university for further testing.

The expedition lasted from l6th November until 18th December 1963. A little over three weeks of this time was spent on the sea-ice between Ross Island and Butter Point. Altogether twenty-one attempts were made to find mud, and three were successful. The following table shows the results of each attempt.