Investigating the Linkage Between Spiral Trough Morphology and Cloud Coverage on the Martian North Polar Layered Deposits.

The martian North Polar layered deposits (NPLD) are composed of alternating water‐ice and dust‐rich layers resulting from atmospheric deposition and are key to understanding Mars climate cycles. Within these deposits are spiral troughs whose migration affects deposition signals. To understand the relationship between NPLD stratigraphy and Martian climate, we must identify modern‐day drivers of NPLD ice migration. Prevailing theory posits migration driven by upstream‐migrating bed undulations bounded by hydraulic jumps, caused by katabatic winds flowing over trough walls with asymmetric cross‐sectional relief. This is supported by trough‐parallel clouds, whose formation has been attributed to hydraulic jumps. We present a cloud atlas across the Martian north pole using ∼13,800 THEMIS images spanning ∼18 Earth years. We find trough‐parallel clouds in ∼400 images, with regions nearer to the pole having higher cloud frequency. We compare spiral trough geometry to our cloud atlas and find regions with trough‐parallel clouds often correlate with metrics associated with modern‐day sublimation‐deposition cycles (i.e., relief and asymmetry), but not always. In some regions, troughs with morphologies conducive to cloud formation have no clouds. Overall, trough geometry varies greatly across the deposits, both within and between troughs, suggesting localized differences in deposition relative to migration, varying katabatic wind intensities, differing past climatic states influencing the troughs, varying trough initiation properties, or the possibility of additional mechanisms for trough initiation and migration (e.g., in situ trough erosion). Understanding what controls trough shape variability across the NPLD and how these controls change through time and space is key when interpreting Martian paleoclimate. Plain Language Summary: The Martian North polar ice cap is composed of layers of water‐ice and dust deposited from the atmosphere, and differences in their thicknesses are thought to be the result of climate variations. Interpretations of the climate recorded in these layers can be affected by other processes that can deposit or erode ice. One process we need to understand is the migration history for the large spiraling troughs that occur across the ice cap, which tend to have asymmetric wall slopes and reliefs. The leading theory suggests that their migration is driven by ice ablation from winds that flow down the higher trough wall, and deposition (and cloud formation) when the wind hits the trough floor and decelerates. We present an updated record of cloud coverage across the ice cap using orbital images spanning ∼18 Earth years and analyze ∼3,000 trough cross‐sections to compare trough shape to cloud location. We find regions with clouds often correlate with trough shapes associated with modern‐day sublimation‐deposition cycles (wall asymmetry), but often asymmetric troughs have no clouds, or the troughs are symmetric. The fact that trough shape changes across the ice cap suggests that ice transport processes are variable and need to be considered when interpreting paleoclimate. Key Points: The spiral troughs on Mars' northern polar layered deposits (NPLD) have highly variable geometry, both within a trough and between troughsThe presence of trough‐parallel clouds, indicative of katabatic jumps and active trough migration, are regionally variable across the NPLDThe trough shape most conducive to the formation of katabatic jumps and generating clouds is not as widespread as previously suggested [ABSTRACT FROM AUTHOR]