The design and use of a marine heat probe with capability for measuring thermal conductivity insitu with high accuracy, and providing digital acoustic transmission of data to the ship, is described. The instrument employs the ‘violin bow’ strength member and parallel sensor string configuration suggested by C. R. B. Lister. Several hundred measurements have been made in the deep ocean on multipenetration or ‘pogostick’ profiles using a 3 m probe and in deep inlets of western Canada using a 7 m probe. The insitu thermal conductivity technique using a calibrated heat pulse has been studied in detail through laboratory calibration of the probe in materials of known conductivity, through numerical models, and through comparison of insitu measurements with needle probe measurements on sediment cores taken from the same sites. The insitu technique permits a conductivity accuracy of better than ±5% with a recording time of 7 minutes following 7 minutes in the bottom to establish the geothermal gradient. The pulse heating is also more energy efficient than the conventional continuous heating technique.

The measurement of marine geothermal heat flow by a multipenetration probe with digital acoustic telemetry and insitu thermal conductivity

A west-to-east traverse of 24 heat flow measurements was made across the Caribbean Sea floor from the eastern Venezuelan basin to 80 km east of the Lesser Antilles arc crest. The resulting heat flow profile includes an increase from basin values in the eastern Venezuelan basin and a zone of high values extending the length of the transect. Superimposed on this zone are two heat flow peaks containing maximum values, one at the Aves swell and the other at the Lesser Antilles arc. Based on 21 acceptable values, average heat flows were 1.87 heat flow units (1 HFU=1 ..mu..cal cm/sup -2/s/sup -1/) (8 values) for basin regions, 3.63 HFU (9 values) for the Aves swell peak, and 4.16 HFU (4 values) for the Lesser Antilles are peak. High heat flow is expected for the Lesser Antilles arc, the present site of seismic and volcanic activity associated with subduction of the North American plate at the West Indies trench. The heat flow peak at the Aves swell agrees with an island arc formation for this presently inactive feature, with its high heat flow anomaly attributed to radiogenic heat sources concentrated during subduction in the past. Both the Aves swell and themore » Lesser Antilles arc are believed to be heated by radiogenic sources accumulated during past subduction, but only the Lesser Antilles arc is now receiving new heat from mechanical processes directly coupled to active underthrusting. This suggests that differences in the two heat flow peaks at the Aves swell and Lesser Antilles arc reflect the relative importance of different heat-producing mechanisms at island arcs.« less

Heat flow in the eastern Caribbean

Marine heat flow is of great significance for the formation and occurrence of seabed oil, gas and gas hydrate resources. Geothermal gradient is an important parameter in determining the thickness of the hydrate stability zone. The northern slope of the South China Sea is rich in gas hydrate resources. Several borehole drilling attempts were successful in finding hydrates in the Shenhu area, while others were not. The failures demand further study on the distribution regularities of heat flow and its controlling effects on hydrate occurrence. In this study, forty-eight heat flow measurements are analyzed in the Shenhu gas hydrate drilling area, located in the northern South China Sea, together with their relationship to topography, sedimentary environment and tectonic setting. Canyons are well developed in the study area, caused mainly by the development of faults, faster sediment supply and slumping of the Pearl River Estuary since the late Miocene in the northern South China Sea. The heat flow values in grooves, occurring always in fault zones, are higher than those of ridges. Additionally, the heat flow values gradually increase from the inner fan, to the middle fan, to the external fan subfacies. The locations with low heat flow such as ridges, locations away from faults and the middle fan subfacies, are more conducive to gas hydrate occurrence.

The characteristics of heat flow in the Shenhu gas hydrate drilling area, northern South China Sea

Flume studies have shown that the threshold velocity of a Woodhead-type sea-bed drifter is reduced in response to the superimposition of wave-induced horizontal (orbital) velocities. A graph is presented to aid in the estimation of the magnitude of the reduction.

The threshold of movement of the Woodhead sea-bed drifter under unidirectional and oscillatory flows, separately and in combination

The standard Ewing heat probe frame has been improved through the design of a new takedown model whose parts are held together by lynch pins. When a 600 lb (272 kg) unit of this type is taken apart, the heaviest single piece of the dismantled unit weighs only 75 lb (34 kg). This makes it feasible for one person to handle, transport, and assemble the new unit. A central, main support member of a heat probe using this frame can be suspended over the side of a research vessel while the heavier temperature recorder and ballast weights are attached by means of the quickaction lynch pins. This makes it possible to use this device on relatively small vessels which are not designed for coring work, having a minimum of free deck space and without launching platforms or hydraulic A-frame booms.

An improved Ewing heat probe frame

A seabed drifter study of near-bottom circulation in North Carolina shelf waters

A versatile probe for simultaneous studies of heat flow and near-bottom water parameters has evolved through modifications of the Bullard heat probe frame Suitable sensor arrays have been used with this instrument to study (1) heat flow through the ocean floor, (2) water column temperature structure, (3) near-bottom current speeds, and (4) the differential cooling of water-column temperature sensors placed in a current speed gradient Some of the advantages of such a modified Bullard probe are: (1) several parameters, including heat flow, can be measured across the sediment-water interface simultaneously, (2) the instrument frame is rigidly pinned to the ocean floor during measurement, permitting true Eulerian measurement in the water column with no effects of ship movement, swaying moorings or cable oscillation, and (3) the device is inexpensive and simple

Ben J. Korgen

Papers

An improved Ewing heat probe frame

A seabed drifter study of near-bottom circulation in North Carolina shelf waters

Extending the versatility of the Bullard heat probe