Signals of astronomical climate forcing in the exposure topography of the North Polar Layered Deposits of Mars

Abstract

Using high‐resolution topography, we link the stratigraphy of layered ice deposits at the north pole of Mars to astronomically driven climate variability. Observations of trough exposures within these deposits are used to construct virtual ice cores at 16 sites, to which we apply wavelet analysis to identify periodicities in layer properties. To confidently relate these periodicities to climatic forcing, we identify overlapping dominant stratigraphic wavelengths and compare their ratios to that of the two dominant modes of insolation variability. The average ratio of stratigraphic wavelengths in the profiles is 1.9 ± 0.1, lower than the ratio of 2.3 between dominant insolation periodicities. A similar analysis of synthetic stratigraphic profiles created with a climate‐driven model of ice and dust accumulation shows that this lower stratigraphic ratio is a natural consequence of time‐variable ice accumulation rates.

Timescales of the Climate Record in the South Polar Ice Cap of Mars

“…Second, the NPLD wavelengths themselves are similar to those detected in PUL. Lastly, the insolation periodicities inferred to have forced NPLD accumulation (Becerra et al, ) are the same ones that we infer to have forced SPLD accumulation.…”

“…Given that protrusion is likely a better stratigraphic property for paleoclimate studies (Becerra et al, , ), we present analysis of protrusion profiles as our nominal results, but analysis on profiles of local slope and brightness are included in Table S2.…”

“…Intuitively, if the ratios agree, each of the stratigraphic wavelengths can be related to the orbital periodicities to calculate average accumulation rates and time spans. However, stratigraphic ratios in the NPLD were found to be lower than the insolation forcing ratio by as much as 30% (Becerra et al, ). Models of the NPLD accumulation (Becerra et al, ; Hvidberg et al, ) showed that such lower ratios are consistent with orbital forcing if the relationship between ice accumulation and insolation is nonlinear.…”

“…The wavelet transform of each profile is computed by normalizing the profiles to zero mean and unit variance and then convolving with the selected wavelet function (see supporting information). The wavelet power spectrum (WPS) is the square of the real part of the transform and shows the change in power with wavelength and depth (Becerra et al, ; Torrence & Compo, ). In the WPS, the abscissa of peaks in power represent dominant wavelengths in the profile (e.g., Figure b).…”

Islands of ice on Mars and Pluto

“…Many studies have used remote sensing observations of the NPLD in an attempt to quantify Martian paleoclimate, with a particular focus on correlating icy stratigraphy with the planet's orbital variations. These studies have yielded promising but uncertain results (e.g., Becerra et al, ; Cutts & Lewis, ; Laskar et al, ; Milkovich & Head, ; Perron & Huybers, ; Sori et al, ). The ultimate goal of deciphering the paleoclimate record in polar ice on Mars is progressing but incomplete.…”