Obliquity dependence of the formation of the martian polar layered deposits

Abstract

Mars' polar layered deposits (PLD) are comprised of layers of varying dust-to-water ice volume mixing ratios (VMR) that are thought to record astronomically-forced climatic variation over Mars' recent orbital history. Retracing the formation history of these layers by quantifying the sensitivity of deposition rates of polar material to astronomical forcing is critical for the interpretation of this record. Using a Mars global climate model (GCM), we investigate the sensitivity of annual polar water ice and dust surface deposition to a variety of obliquity and surface water ice source configurations at zero eccentricity that provide a reasonable characterization of the evolution of the PLD during recent low-eccentricity epochs. The GCM employs a fully interactive dust lifting/transport scheme and accounts for the coupling effects of the physics of dust and water on the transport and deposition of water ice and dust. Under a range of tested obliquities (15°-35°), the predicted net annual accumulation rates range from-1 mm/yr to +14 mm/yr for water ice and from 0.003-0.3 mm/yr for dust. GCM-derived accumulation rates are ingested into an integration model that simulates polar accumulation of water ice and dust over five consecutive obliquity cycles (~700 thousand years) during a low eccentricity epoch. A subset of integration model simulations predict combined north polar water and dust accumulation rates that correspond to the observationally-inferred average growth rate of the north PLD (0.5 mm/yr). These integration model simulation results are characterized by net water transfer from the south to the north polar region. In the north, a ~230 m-thick deposit is accumulated over ~700 thousand years. Three types of layers are produced per obliquity cycle: a ~30 m-thick dust-rich (20-30% dust VMR) layer that forms at high, a ~0.5 m-thick dust lag deposit (pure dust) that forms at low obliquity, and two ~10 m-thick dust-poor (~3%) layers that separate the dust rich layers and form when obliquity is increasing or decreasing. The ~30 m-thick dust-rich layer is reminiscent of a ~30 m scale length feature derived from analysis of visible imagery of north PLD vertical structure, while the ~0.5 m-thick dust lag is only a factor of ~2 smaller than observed "thin layers". Overall,

Stratigraphic and Isotopic Evolution of the Martian Polar Caps From Paleo‐Climate Models

“…In addition to the atmospheric humidity described above, the evolution of surface ice was also tracked. Following past work (Emmett et al, 2020;Levrard et al, 2004Levrard et al, , 2007Madeleine et al, 2009), we track the evolution of surface ice at past orbital parameters. Here, we significantly extend the range of conditions studied, use more realistic ice distributions that are based on high obliquity GCM simulations and geologic evidence (Forget et al, 2006;Head et al, 2005), and provide interpretations based on the humidity patterns above, to derive a relation between polar cap growth rate and orbital elements.…”

“…The length and intensity of the seasons are also governed by the eccentricity and perihelion precession, which have periods of 100 and 51 kyr, respectively. Previous modeling work using GCMs (Emmett et al, 2020;Levrard et al, 2004Levrard et al, , 2007) demonstrated that at low obliquity, when a tropical ice source is available, net transport of ice is from the equatorial region to the poles. Net polar ice gain occurs when obliquity is below a threshold of ∼35° for a circular orbit, but the precise value depends on other orbital elements, such as the perihelion position, and on assumed model parameters such as dust and ice properties (Madeleine et al, 2009).…”

Water Deposition Rates onto Mars' South Polar Massive CO2 Ice Deposit

“…One caveat is that Emmett et al (2020) find that south polar dust deposition rate 𝑟 dust increases with increasing 𝜀. Specifically, they find, for 𝜀 = 15, 20, and 25 ∘ : 𝑟 dust = ~0.005 mm yr -1 ; for 𝜀 = 30 ∘ : 𝑟 dust = ~0.02 mm yr -1 , and for 𝜀 = 35 ∘ : 𝑟 dust = ~0.3 mm yr -1 .…”

Stratigraphic and Isotopic Evolution of the Martian Polar Caps from Paleo-Climate Models

“…In addition to the atmospheric humidity described above, the evolution of surface ice was also tracked. Following past work (Levrard et al, 2007;Emmett et al, 2020;Levrard et al, 2004;Madeleine et al, 2009), we track the evolution of surface ice at past orbital parameters. Here, we significantly extend the range of conditions studied, use more realistic ice distributions that are based on high obliquity GCM simulations and geologic evidence (Forget et al, 2006;Head et al, 2005), and provide interpretations based on the humidity patterns above, to derive a relation between polar cap growth rate and orbital elements.…”

“…The length and intensity of the seasons are also governed by the eccentricity and perihelion precession, which have periods of 100 kyr and 51 kyr, respectively. Previous modeling work using GCMs (Levrard et al, 2004(Levrard et al, , 2007Emmett et al, 2020) demonstrated that at low obliquity, when a tropical ice source is available, net transport of ice is from the equatorial region to the poles. Net polar ice gain occurs when obliquity is below a threshold of ∼35 • for a circular orbit, but the precise value depends on other orbital elements, such as the perihelion position, and on assumed model parameters such as dust and ice properties (Madeleine et al, 2009).…”