Pioneering deep sea equipment donated to Science Museum

Oceanographic equipment developed by a University of Aberdeen academic and a colleague from Brunel University dating back more than 30 years is this month being donated to the Science Museum in London.

Dr Alister Macdonald, who has since retired from the Physiology Department at the University, and Dr Ian Gilchrist, from the Mechanical Engineering Department, Brunel University, London, collaborated together for almost 15 years, from 1970 to the mid 1980s. The object of their collaboration was the study of living deep sea animals and the development of new benthic (ie sea floor) traps to recover the animals from any ocean depth, at their ambient high pressure.

The work was supported by a series of Natural Environment Research Council (NERC) grants.

Ocean depths of four kilometres cover over half the surface of our planet and in restricted areas deep sea trenches extend to 10km. Despite the high water pressure and the low temperatures (less than 4^oC), animals and bacteria inhabit the whole environment. Deep sea pressures are sufficient to affect the reactions underlying the biochemistry and physiology of the organisms, and indeed, if applied to shallow water animals (and humans) paralyse and kill them.

The approach by Drs Macdonald and Gilchrist was to retrieve living animals from the deep sea at their normal high ambient pressure and low temperature. This required the design and fabrication of special high pressure vessels, windows, large diameter valves, and hydraulic circuitry, all to be used on research ships at sea. 

The pressure-retaining benthic traps weighed about 200kg (more than 30 stone). They were cast to the ocean floor where small Amphipod crustacea that (about 2cm long) crawled through the entrance valve and swam inside. The valve then closed at depth and the trap's ballast was discharged to enable large buoyancy packs to float it to the surface, under acoustic surveillance from the mother ship. Once on board the ship, the trap served as an observational pressure vessel, allowing the activity of the Amphipods to be observed at pressures higher and lower than normal. Using this approach it was found that animals from depths greater than 2km (where the pressure is 200 atmospheres ie 200 times our normal pressure) became immobilised when decompressed to normal atmospheric pressure, but they could be revived if restored to their pressure of origin.

These results led to a series of ship board, physiological experiments on skeletal muscle, heart muscle and axons rapidly isolated from deep sea fish, freshly trawled from 4,000m depths (400 atmospheres pressure) which appeared to be dead.  The isolated preparations were restored to the pressure and temperature from which the fish had been trawled and, over a period of hours, gradually resumed normal function (ie the muscles twitched on stimulation and the axons conducted impulses).

Dr Macdonald is extremely pleased that the Science Museum in London has acquired some of the oceanographic equipment he worked on back in the 1970s, including a pressure-retaining trap and a set of high pressure windows in various states of destructive testing and stress analysis.  He said: "Dr Gilchrist and I collaborated decades ago.  We established the susceptibility of deep sea animals to higher and lower than normal pressure and the phenomenon of pressure resuscitation.  This opened up the prospect of investigating high pressure adapted, classical physiological preparations such as nerve and muscle. We also showed that generations of deep sea biologists have been mistaken when observing what they thought were dead animals in deep sea trawls."

The pressure-retaining traps were the forerunner of devices used to collect deep sea bacteria at high pressure.