The ocean floor presents a particularly harsh environment in which to carry out electrical measurements, with pressures of up to 600 atm (60 MPa), temperatures of around 3 °C, and no possibility of radio contact with instrumentation. Furthermore, seawater is a corrosive, conductive fluid. Thus, progress in the field of electrical conductivity studies has largely followed the availability of reliable underwater technology and has not become truly routine until recently.
Most electromagnetic methods can be adapted for seafloor use, but the high conductivity of seawater dominates both how data are collected and how they are interpreted. Seawater conductivity depends on salinity and temperature; in practice salinity variations are too small to be significant and so to a good approximation seawater conductivity is given by (3 + T/10) S/m where T is temperature in degree celsius. The bulk of the ocean thus has a resistivity of about 0.3 Ωm, with warmer surface waters 0.2 Ωm.
DC resistivity...
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Constable, S. (2007). Conductivity, Ocean Floor Measurements. In: Gubbins, D., Herrero-Bervera, E. (eds) Encyclopedia of Geomagnetism and Paleomagnetism. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4423-6_30
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