From [1] above: > atmospheric, [marine] carbonate, and plant derived δ13C values all differ. So, there is a mineral process that can explain change in isotope

From [1] above: > atmospheric, [marine] carbonate, and plant derived δ13C values all differ. So, there is a mineral process that can explain change in isotope ratio, which requires water. And also a biological process with the same outcome, also requiring water. In other words, this looks like a solid new piece of evidence in support of presence of liquid water on Mars in the past. Evidence of life though? That is less certain.