Abstract:
A hydrodynamic model incorporating a self-consistent treatment of ocean selfattraction
and loading (SAL), and a physically based parameterization of internal tide (IT)
drag, is used to assess how accurately barotropic tides can be modeled without benefit of
data, and to explore tidal energetics in the last glacial maximum (LGM). M₂ solutions
computed at high resolution with present day bathymetry agree with estimates of
elevations from satellite altimetry within 5 cm RMS in the open ocean. This accuracy, and
agreement with atlimetric estimates of energy dissipation, are achieved only when SAL
and IT drag are included in the model. Solutions are sensitive to perturbations to
bathymetry, and inaccuracies in available global databases probably account for much of
the remaining error in modeled elevations. The ≈100 m drop in sea level during the LGM
results in significant changes in modeled M₂ tides, with some amplitudes in the North
Atlantic increasing by factors of 2 or more. Dissipation is also significantly changed by the
drop in sea level. If IT drag estimated for the modern ocean is assumed, dissipation
increases by about 50% globally, and almost triples in the deep ocean. However, IT drag
depends on ocean stratification, which is poorly known for the LGM. Tests with modified
IT drag suggest that the tendency to a global increase in dissipation is a robust result,
but details are sensitive to stratification. Significant uncertainties about paleotides thus
remain even in this comparatively simple case where bathymetry is well
constrained.
