Are Tides Controlled by Latitude?

Abstract

A common belief about tidal sedimentation, based on equilibrium-tide theory that predicts the existence of two ocean-surface bulges centered at low latitudes, is that tides are always larger near the equator and negligible at high latitudes. This is a misconception, because the real-world tide is not explained well by equilibrium-tide theory. Instead, the tide behaves as a shallow-water wave that is guided around the world by the continents. Tidal ranges (and tidal-current speeds) increase as the tidal wave propagates onto and across continental shelves; especially large ranges and fast currents can occur in coastal embayments and in straits that join two larger bodies of water. Tide models demonstrate that tides in shallow water (< 100 m) have amplitude peaks at 50°-70°N and 50°S that are associated with especially wide continental shelves and coastal embayments in which the tidal wave is close to resonance. The small tides characterizing most polar areas today are the result of local geomorphic features: the Arctic Ocean is too small to have its own tide and has only a small connection to the Atlantic Ocean that prevents effective northward propagation of the tidal wave; and Antarctica has narrow and deep continental shelves that do not accentuate the tide. Nevertheless, there are local areas in both the Arctic and Antarctic with favorable geomorphology that have macrotidal ranges. Thus, the latitudinal distribution of large tides is contingent on the plate-tectonic and sea-level history of the Earth, and changes over geologic time as the configuration of the ocean basins changes. Because coastal sedimentation is controlled by the relative importance of tidal currents and waves, the abundance of tide-dominated deposits might not reflect perfectly the latitudinal distribution of large tides. Thus, the small size of waves in the equatorial zone might cause preferential development of tidal deposits near the equator.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016