Dynamic circulation of interstitial seawater in a Jamaican fringing reef

Abstract

Twelve 7.62 cm diameter cores were taken along three and a half kilometers of coastline in the vicinity of Discovery Bay, Jamaica, to document the distribution of dolomite previously described (Mitchellet al., 1987). Water was observed to flow actively in and out of the open holes, which range in water depths from 6 to 13 meters. Most of the shallowest holes, and the single deepest one, “exhale” slowly and continuously, little affected by the wind-driven surge. Holes at intermediate depths exhibit a net flow of water into the reef, “breathing” asymmetrically with the wind-driven surge. In one case an integrated current velocity of 86 cm sec⁻¹ was measured over a five minute interval into a three meter deep open hole. Astronomical tides, local wind-driven surge, and dispersion due to meteoric water discharge are apparently not direct causes of the phenomenon.

Under normal conditions, dynamic interstitial fluid flow can provide the conditions necessary for extensive submarine cementation (and dolomitization?). Under abnormal conditions (natural fractures or man-made holes), extreme current velocities may be capable of causing the kinds of textures observed in Neptunian dikes and sills in ancient reefs.