Circumpolar ocean stability on Mars 3 Gy ago

Abstract

What was the nature of the Late Hesperian climate, warm and wet or cold and dry? Formulated this way the question leads to an apparent paradox since both options seem implausible. A warm and wet climate would have produced extensive fluvial erosion but few valley networks have been observed at the age of the Late Hesperian. A too cold climate would have kept any northern ocean frozen most of the time. A moderate cold climate would have transferred the water from the ocean to the land in the form of snow and ice. But this would prevent tsunami formation, for which there is some evidence. Here, we provide insights from numerical climate simulations in agreement with surface geological features to demonstrate that the Martian climate could have been both cold and wet. Using an advanced general circulation model (GCM), we demonstrate that an ocean can be stable, even if the Martian mean surface temperature is lower than 0 °C. Rainfall is moderate near the shorelines and in the ocean. The southern plateau is mostly covered by ice with a mean temperature below 0 °C and a glacier return flow back to the ocean. This climate is achieved with a 1-bar CO2-dominated atmosphere with 10% H2. Under this scenario of 3 Ga, the geologic evidence of a shoreline and tsunami deposits along the ocean/land dichotomy are compatible with ice sheets and glacial valleys in the southern highlands.

Billion-year trends in the aridity of river-forming climates on Mars

“…The northern hemisphere XH permits a late-stage ocean, consistent with some models (e.g., Di Achille & Hynek 2010, Schmidt et al 2022). However, the case for a Mars ocean remains equivocal: delta locations suggest deltas drained into large lakes, not an ocean (e.g.…”

Aqueous alteration of the Vastitas Borealis Formation at the Tianwen-1 landing site

“…The VBF was previously proposed to be formed from the sedimentary deposits in a standing body of water either from an Upper Hesperian ocean 6,10,13,14 , outflow channels 5,16 , or compaction and drainage activities 17,18 , which experienced subsurface ice-related processes 1,4,19,20 and was covered by globally homogenized Mars surface dust. Based on SWIR analyses, the VBF-ZR targets are composed of amorphous aluminosilicates (allophane and imogolite/opal) and High-Ca pyroxene that are widely distributed in soils and rocks along the traverse path of the ZR rover.…”

“…Based on those observations, several previous studies proposed that the VBF material is a sedimentary deposit from a standing body of water that might be an Upper Hesperian ocean 6,[10][11][12][13] . A circumpolar ocean was also proposed based on a coupled model with a dynamic ocean and atmosphere 14 . In addition, the pebbles, cobbles, and boulders in VBF may be deposited by a catastrophic flood 15 , suggesting that the VBF has flood deposits from outflow channels 5,16 .…”

Megatsunamis and microbial life on early Mars

“…Many researchers today cautiously discuss about the Martian palaeo-ocean and its shorelines, and despite some geological evidence, the issue of the existence of an ocean on early Mars remains in debate (Schmidt et al, 2022).…”