  River deposits are one of the main lines of evidence that tell us that Mars
once had a climate different from today, and so changes in river deposits with
time tell us something about how Mars climate changed with time. In this study,
we focus in on one sedimentary basin - Aeolis Dorsa - which contains an
exceptionally high number of exceptionally well-preserved river deposits that
appear to have formed over an interval of $>$0.5 Myr. We use changes in the
river deposits' scale with stratigraphic elevation as a proxy for changes in
river paleodischarge. Meander wavelengths tighten upwards and channel widths
narrow upwards, and there is some evidence for a return to wide
large-wavelength channels higher in the stratigraphy. Meander wavelength and
channel width covary with stratigraphic elevation. The factor of 1.5-2
variations in paleochannel dimensions with stratigraphic elevation correspond
to $\sim$2.6-fold variability in bank-forming discharge (using standard
wavelength-discharge scalings and width-discharge scalings). Taken together
with evidence from a marker bed for discharge variability at $\sim$10m
stratigraphic distances, the variation in the scale of river deposits indicates
that bank-forming discharge varied at both 10m stratigraphic (10$^2$ - 10$^6$
yr) and $\sim$100 m stratigraphic (10$^3$ - 10$^9$ yr) scales. Because these
variations are correlated across the basin, they record a change in basin-scale
forcing, rather than smaller-scale internal feedbacks. Changing sediment input
leading to a change in characteristic slopes and/or drainage area could be
responsible, and another possibility is changing climate ($\pm$50 W/m$^2$ in
peak energy available for snow/ice melt).
