| Abstract | A long-standing question in geodynamics is the cause of deviations of ocean depth or
seafloor topography from the prediction of a cooling half-space model (HSC). Are the
deviations caused entirely by mantle plumes or lithospheric reheating associated with
sublithospheric small-scale convection or some other mechanisms? In this study we
analyzed the age and geographical dependences of ocean depth for the Pacific plate, and
we removed the effects of sediments, seamounts, and large igneous provinces (LIPs),
using recently available data sets of high-resolution bathymetry, sediments, seamounts,
and LIPs. We found that the removal of seamounts and LIPs results in nearly uniform
standard deviations in ocean depth of 300 m for all ages. The ocean depth for the Pacific
plate with seamounts, LIPs, the Hawaiian swell, and South Pacific super-swell excluded
can be fit well with a HSC model till 80–85 Ma and a plate model for older seafloor,
particularly, with the HSC-Plate depth-age relation recently developed by Hillier and
Watts (2005) with an entirely different approach for the North Pacific Ocean. A similar
ocean depth-age relation is also observed for the northern region of our study area with no
major known mantle plumes. Residual topography with respect to Hillier and Watts’ HSCPlate
model shows two distinct topographic highs: the Hawaiian swell and South
Pacific super-swell. However, in this residual topography map, the Darwin Rise does not
display anomalously high topography except the area with seamounts and LIPs. We also
found that the topography estimated from the seismic model of the Pacific lithosphere of
Ritzwoller et al. (2004) generally agrees with the observed topography, including the
reduced topography at relatively old seafloor. Our analyses show that while mantle
plumes may be important in producing the Hawaiian swell and South Pacific super-swell,
they cannot be the only cause for the topographic deviations. Other mechanisms,
particularly lithospheric reheating associated with ‘‘trapped’’ heat below old lithosphere
(Huang and Zhong, 2005), play an essential role in causing the deviations in topography
from the HSC model prediction
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