Quantifying Latitudinal Variations of Continental Physiography

The spatial distribution of elevations of continents is a primary expression of complex interactions between tectonic and climatic systems. As a geomorphic record, spatial variations of continental physiography afford some insight into the relative importance of tectonic and climatic processes in predicating Earth-surface elevations. Assuming that physiographic measurements in a spatial series are generally equivalent to those in an unnormalized time series, we here attempt to quantify the dependence on climate of slopes and elevations of continental surfaces as reported with GTOPO30. In order to determine the covariance of land surface physiography with climate, we first tabulated a global continental hypsography and then a continental hypsography for each one-degree band of latitude. The shapes of both global and latitudinal hypsometries can be largely explained by an exponential decrease in elevation away from some maximum value; maximum elevations exhibit no systematic variation with latitude and likely reflect uncorrelated variation in the intensity and timing deformation. After normalizing each latitudinal hypsography to a common maximum elevation and total land area, neither best-fit exponentials nor residuals between model and DEM-derived data exhibited any apparent latitudinal dependence. From this we observe that continental physiography manifest as large-scale, relative hypsometry is unrelated to climatic gradients. After then calculating slope for every ice-free pixel of GTOPO30, we graphed the slope of each pixel as a function of the pixels elevation and latitude. From this it was determined that slopes on continents covary with latitude and, by inference, climate. Although slope depends mostly upon elevation, slope correlates to a small degree with latitude such that higher latitudes generally have steeper slopes at lower elevations. By making this observation and by observing that relative hypsometries do not vary by latitude, we conclude that higher latitudes are more dissected and that changes in the importance of various modes of continental denudation as predicated by climate are the primary mechanism for this state.