Perennially ice‐covered lake facies as proxies for ice cover properties and climate: Insights from Lake Joyce, Antarctica

ABSTRACT Process‐based depositional models for perennially ice‐covered lakes (PICLs) are important for interpreting palaeolake deposits and their connection to past climate. PICLs are only stable under specific climate states, and unlike other ice‐free or seasonally ice‐covered lakes, PICL deposits generally have bimodal grain sizes: mud introduced by streams and glaciers and moderately sorted medium to coarse sand deposited as disseminated grains, mounds and ridges from the ice cover. Previous work implies that ice properties influence the mud‐to‐sand ratio and sand depositional style. Here we present multi‐year observations from Lake Joyce, Antarctica, demonstrating how ice cover properties influence deposition to help inform interpretations of climate from the sedimentary record. Lake Joyce's ice cover had smooth to rough textures with rougher ice trapping more sediment and forming multi‐grain sediment pods, and smooth ice containing scattered grains. Low‐albedo medium sand grains preferentially melted into the ice over higher albedo grains and those that are finer and coarser. Thicker pods slowed underlying ice melt, whereas thinner pods accelerated it. Grains migrated downwards and accumulated at an equilibrium depth which was shallower than the ice cover thickness. Sediment pods commonly contained inverse grading, resulting from deflation and preferential melting of finer grains into the ice. These observations help inform PICL deposit interpretations: pods in rough ice result in sand mounds and ridges, while scattered grains on smooth ice lead to disseminated grains. Deposits have a narrow grain‐size range due to the preferential melting of medium sand, and inverse grading in mounds mirrors that of pods. Our observations suggest that ice roughness and thickness control where and how much sediment accumulates, its vertical migration through the ice and depositional style. Temporal or spatial variations in ice properties may be preserved as stratigraphic or lateral facies changes. Because ice properties are climate‐dependent, stratigraphic variations in PICL facies may be used as palaeoclimate indicators if found on Earth and Mars.