Orbital Forcing of Martian Climate Revealed in a South Polar Outlier Ice Deposit

Deciphering paleoclimate on Mars has been a driving goal of Martian science for decades. Most research has addressed this issue by studying Mars' large polar layered deposits (PLDs) as a paleoclimate proxy, but the certainty to which we know the link between climate and orbit is debated. Here, we instead consider the record of other, smaller ice deposits located within craters separated from the PLDs using images from NASA's High Resolution Imaging Science Experiment camera and signal processing techniques. We show that the climate record in Burroughs Crater (72.3°S, 116.6°E) contains robust evidence of orbital forcing, with periodicities that have wavelengths of 15.6 and 6.5 m. The ratio of these dominant wavelengths is 2.4, the same as the ratio between the periods of Mars' obliquity changes and orbital precession. This result suggests orbital control of recent Mars climate, and would imply an average ice accumulation rate of 0.13 mm/yr over 4.5 Myr in this region. Plain Language Summary Understanding the relationship between Martian climate and changes in the planet's axial tilt and orbit around the Sun is one of the most important goals in Mars science. Most past studies conducted to address this goal have involved study of the polar ice caps, huge sheets of H2O ice at the north and south pole. Here, we instead study smaller ice deposits (10s of km in diameter) near the north and south pole, but located within craters and separated from the larger polar caps. We find that the ice deposit in Burroughs Crater contains particularly good evidence that recent Martian climate is strongly controlled by changes in the planet's orbit and axial tilt. Key Points The icy record in Burroughs crater shows Martian climate is strongly controlled by astronomical forcing The average ice accumulation rate in this region was 0.13 mm/yr The deposit in Burroughs crater represents a younger, more easily decipherable climate record than that in the SPLD