Observation of sub‐inertial internal tides in McMurdo Sound, Antarctica

Abstract

McMurdo Sound, Antarctica, at 78°S is poleward of the critical latitudes for both diurnal and semi‐diurnal internal tides, which are, respectively, 30°S and 75°S. Yet fieldwork during April 2003 and November 2004 observed energy at both frequencies. High temporal resolution density profiles in April 2003 and mooring observations at 240 m depth in November 2004 show a diurnal internal tide with displacements of up to 12 m. The horizontal decay length scales for diurnal evanescent internal tides indicate that they were locally generated. The November 2004 mooring observations also show a semi‐diurnal tide with displacements up to 12 m, although some of the energy in these waves could be baroclinic inertial motion, which has a similar frequency at this latitude. The semi‐diurnal internal waves have a larger decay length scale than the diurnal internal waves, so are not necessarily locally generated.