New insights from new instruments for physics and chemistry

Upper Ocean Structure and Air-Sea Interaction

To investigate the structure of the upper ocean and the marine atmospheric boundary layer, the Royal Society organized several Joint Air-Sea Interaction (JASIN) experiments in the 1970s. Henry Charnock chaired the planning committee, with Raymond Pollard as Scientific Coordinator. Three ships were needed, at minimum, to release radiosondes to observe horizontal gradients in the atmosphere (JASIN ’72) but no fewer than 17 ships and 3 aircraft from 7 countries signed up to the final experiment JASIN ’78. Arthur Fisher solved the logistics problems by taking over empty wharfs on the Clyde, where there were memorable intership receptions.

Several new instruments on Discovery  resolved the spatial structure of the ocean, from mesoscale eddies (whose structure and ubiquity were being established) to upper ocean fronts. In JASIN ’78 the new, accurate and reliable Neil Brown CTD was mounted on SeaSoar and towed behind Discovery  at 8 kn, profiling between the surface and over 300 m, resolving spatial structure at horizontal scales down to 4 km. Repeated circuits were made round a drifting spar buoy instrumented with current meters.

JASIN ’78 culminated in a Discussion Meeting at the Royal Society, with results published in its Philosophical Transactions. Perhaps the major oceanographic finding was that there are strong horizontal gradients at many scales, so that onedimensional models of the upper ocean are too simplistic. Wave buoys deployed from Discovery on JASIN ’78 also provided valuable ground-truth data for the short-lived SEASAT, the first Earth-orbiting satellite designed for remote sensing of the Earth’s oceans.

Evolution of Marine Chemistry to Geochemistry

Those working in the chemical laboratory on Discovery  in the 1960s concentrated on routine analyses for salinity, dissolved oxygen and the nutrients phosphate, nitrate and silicate. Specialised measurements of organic nutrients, trace metals and particulate carbon and nitrogen were made occasionally. The 1970s saw a real change, with repeatable and reliable vertical profiles of trace metals for the first time. One breakthrough was the realisation of exactly what was needed to avoid contamination. The interplay of a number of chemical elements and biology, in the water column and sediments, began to be studied and understood.

Trace element and particulate analysis required large water volumes, 30 litre Niskin bottles being typical on Discovery  cruise 63 in 1974. Much of the analysis had to be done ashore at Wormley and Southampton University, but “preliminary concentrations” of molybdenum and vanadium could be done aboard. Equipment capability developed rapidly through the decade: a new stainless steel gravity corer was developed, as was a sampler to capture, in situ, pore water from within the sediment.

By 1977 on board analysis benefitted from new gas-liquid chromatography apparatus, enabling dissolved selenium to be measured. This led to new insights on the vertical transport of particulates we now refer to as “marine snow”.

The 1980s: Multidisciplinary science

Research into the feasibility of sub-seabed disposal of high-level radioactive waste in the deep ocean dominated much of the research agenda of IOS, and consequently the cruise schedules for Discovery , in the 1980s. It was a multidisciplinary programme funded by the UK Department of the Environment as part of the international effort coordinated by the Nuclear Energy Agency. DoE placed five contracts with IOS between 1981-85 covering site selection, properties of sediments, biological transfer of material between seabed and surface, benthic boundary layer studies, and dispersion in the NE Atlantic, The total contract value was ca. £6m (1985 prices).

Prior to these contracts IOS wrote a report in 1978 on oceanography related to deep-sea waste disposal, in part drawing upon information the authors had gleaned from cruises on Discovery. Many new staff arrived, and 19 cruises of Discovery, together with cruises on Farnella and Shackleton, took place in the N Atlantic to the Nares Abyssal Plain, the Kings Trough region, and the Cape Verde and Great Meteor East Abyssal Plains.

On board Discovery  a new main winch system and aft davit were designed and fitted to handle and operate large corers and nets systems at greater depths than previously possible. A White-Gill bow thruster for better station keeping and a new midships winch were also added. A variety of novel sensors and equipment was developed including: high resolution seismic profilers, deep-towed and seabed lander photographic systems, a pop-up pore pressure instrument, a laboratory heat probe, corers, in situ pore-water samplers, an in situ deep water particle sampler, instrumented benthic and nearbottom midwater nets, and a system for measuring benthic currents and temperatures (BENCAT). The programme also accelerated development of echosounding neutrally-buoyant floats, sound sources, and autonomous listening stations for float tracking.

The research generated a huge amount of data and insight into the structures and processes within the deep ocean. Different areas of the ocean were assessed for their suitability as potential disposal sites, with later work concentrated at Great Meteor East (GME) on the Madeira Abyssal Plain. Research included the seismic and sedimentological history of different sites and resultant studies of turbidity flows and sequences; the occurrence of glacial erratics; the physical, chemical and geotechnical properties of sediments including in situ measurements of heat flow and pore water pressure gradients; pore water chemistry and the diagenesis and migrations of naturally occurring radionuclides in both oxic and anoxic conditions within sediments; particulate flux and elemental scavenging by particles in the water column; current flows and fronts in the benthic boundary layer near to the seabed; widespread dispersion by ocean currents; the species composition and distributions of benthic fauna and midwater animals throughout the water column and the links between these. In conjunction with the UK’s Building Research Establishment trial deployments of instrumented penetrators were made from Discovery . Designed to free-fall and penetrate into the sediment, these devices used low frequency acoustics to send back information from within the sediments to the ship.

More widely, the research combined model developments with novel observations from a unique suite of sensors. One unexpected discovery was a manganese nodule field at GME, a nodule from which finished up on prime-minister John Major’s desk!

The results were published in a series of IOS reports and in the open literature, and GME remains perhaps the best-known deep ocean site in the world ocean. The overall consensus of the international programme was that, from a technical and scientific viewpoint, sub-seabed disposal could be a feasible option. However, legal and political issues allied to public acceptability concerns have meant that the option has not been taken further.