Subsistence of ice-covered lakes during the Hesperian at Gale crater, Mars

Abstract

Sedimentary deposits characterized by the Mars Science Laboratory Curiosity rover provide evidence that Gale crater, Mars intermittently hosted a fluvio-lacustrine environment during the Hesperian. However, estimates of the CO 2 content of the atmosphere at the time the sediments in Gale crater were deposited are far less than needed by any climate model to maintain temperatures warm enough for sustained open water lake conditions due to the low solar energy input available at that time. To reconcile some of the in-situ sedimentological evidence for liquid water with climate modeling studies, we perform the water budget of evaporation against precipitation to estimate the minimum lifetimes and the rainfall requirements for open water and ice-covered lakes in Gale crater, for a wide range of pressures and temperatures. We found that both open water and ice-covered lakes are possible, and that ice-covered lakes provide better consistency in regards of the low erosion rates estimates for the Hesperian. We incrementally test the existence of open water conditions using energy balance calculations for the global, regional, and seasonal temperatures, and we assess if the preservation of liquid water was possible under perennial ice covers. We found scenarios where lacustrine conditions are preserved in a cold climate, where the resupply of water by the inflow of rivers and high precipitation rates are substituted by an abutting glacier. For equatorial temperatures as low as 240K-255K, the ice thickness ranges from 3-10 m, a value comparable to the range of those for the perennially ice-covered lakes in Antarctica (3-6 m). The ice-covered lake hypothesis is a compelling way to decouple the mineralogy and the climate by limiting the gas exchanges between the sediment and the CO 2 atmosphere, and it eliminates the requirement for global mean temperatures above the freezing point. Not only do ice-covered lakes provide a baseline for exploring the range of possible lake scenarios for Gale crater during the Hesperian that is fully consistent with climate studies, but also they might have been ideal environments to sustain life on Mars.

Glacial lake outburst floods enhance benthic microbial productivity in perennially ice-covered Lake Untersee (East Antarctica)

“…Our findings also have relevance for the potential habitability of CO 2 -depleted lakes on early Mars. As suggested by previous studies 56,57 , well-sealed perennially ice-covered lakes in Antarctica provide relevant analogs that may help explain the lack of observed carbonates in the paleolacustrine sediments of Gale Crater (which was likely an ice-covered lake during the Hesperian 58 ) despite a higher CO 2 level in the atmosphere during that early period of Martian history. As shown in Lake Untersee, with its CO 2 -depleted water column, and sediments nearly carbonate-free, such lakes can still sustain robust benthic microbial communities.…”

Ancient Winds, Waves, and Atmosphere in Gale Crater, Mars, Inferred From Sedimentary Structures and Wave Modeling

“…Kling et al. (2020) noted that their model of an ice‐covered lake does not account for the observed fluvial sedimentary structures. They cite Kite, Halevy et al.…”

“…Alternatively, the lake may usually have been covered with ice, with wave ripples forming only when the ice was absent (Knockfarril Hill member). Models suggest that in a cold low‐density atmosphere a 100‐m‐deep lake would evaporate within tens to thousands of years (Kling et al., 2020). Although this is short on a geological time scale, the time required to form wave ripples is only minutes or hours.…”

“…Grotzinger et al (2015) argued that a lack of recognized glacial and periglacial features (frost wedges, dropstones, glacial tills) suggests a lack of ice on the lake. Using a climate model that balanced water input to the lake, freezing on the bottom of an ice cover, and sublimation of the upper ice surface, Kling et al (2020) calculated that an ice cover of a few meters or tens of meters would have been sufficient to maintain a lake in Gale crater under conditions of an annual mean temperature of 235-270 K and an atmosphere of 0.5 bar. An ice thickness of 30 m would provide enough hydrostatic pressure to prevent underlying water from boiling under frigid temperatures even in an atmosphere thinner than present.…”

“…It is further plausible that at very low atmospheric pressures and low temperatures frost wedging would be eliminated because the sediment would be vacuum freeze-dried before ice could melt and refreeze; such vacuum freeze-drying has been proposed as a technique to preserve sediment cores and prevent them from cracking (Enevold et al, 2019). Kling et al (2020) noted that their model of an ice-covered lake does not account for the observed fluvial sedimentary structures. They cite Kite, Halevy et al (2013) who proposed that fluvial activity might be episodic, but we do not know if it is possible to develop a model that balances these opposing constraints (cold and dry to prevent frost-wedging and wet to provide fluvial inputs of sediment).…”