Images of ocean microstructure

Abstract

Temperature and salinity structures at the molecular diffisuon scale, which create index of refraction anomalies in the ocean, have been observed using the shadowgraph method in an instrument named “SCIMP”. Images of salt fingers — the convective cells driven by the differential diffusivities of heat and salt — were obtained in the Mediterranean Outflow, in the Caribbean, and in the deep Tyrrhenian Sea. The square-packed domains, which the counterflowing fingers form, converge the light in a pattern of bright vertical bands behind diagonal rows of high index fingers. Random alignment of the domains in a field of fingers makes it probable that some domain is aligned with its diagonal rows parallel to the optic axis. Folded interfaces of high gradient in temperature and salinity appeared in images recorded in the upper 300 m in the Caribbean and near the surface in the other regions. The shadowgraph image of a single interface is a line graded dark on the low index side and bright on the high index side. Curved interface surfaces produce an outline of the portion which lies parallel to the optic axis. Several are produced by deeply convoluted interfaces. Images of salt fingers or folded interfaces are an indication of mixing.