On the seawater density in gravity calculations

Abstract

The bathymetry from the continental margin off the Baja California Peninsula, and across the Tonga Trench, are used to quantify the differences in gravitational attraction, arising by considering a constant density ρw = 1030 kg/m3, typically used in marine geophysical studies, versus two global zonal models that describe the seawater density as a function of depth and geodetic latitude. With precision better than 1 μGal, I found that the maximum difference across the continental margin of the Baja California Peninsula is less than 1.5 mGal in the Cedros Deep away from the Continental Rise, while it is less than 0.05 mGal on the Continental Shelf. The maximum difference across the Tonga trench is about 5.3 mGal. Considering that the overall accuracy achieved in typical marine or satellite gravity surveys is at best of 1 mGal, the calculation of the gravity effect due to the seawater layer by either one of the two zonal models may reduce the error budget in stripping-off the gravity effect in deep waters.