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Abstract

The melting of ice sheets directly contributes to ocean mass and volume change. One key metric to keep track of ice-ocean mass exchange is the "ice-sheet contribution to sea-level change" (IS2SL), which is presumed to be a conservative metric that does not depend on what path an ice sheet takes to reach from its initial to final geometry. Conventionally, IS2SL is calculated by quantifying the change in ice volume above flotation. What appears to be a trivial book-keeping task unfolds a layer of complexities while quantifying IS2SL in real-world scenarios where ice sheets, solid Earth, and ocean geometries evolve continuously. Two research groups have independently proposed supposedly general formalisms to quantify IS2SL [1,2]. The two methods do not seem to agree, especially where an ice sheet transits from the grounded to the floating state, or the reverse, much of what happens in marine sectors of Antarctica or the former Laurentide Ice Sheet. In particular, one method appears to predict a path-dependent solution for IS2SL [1], challenging the utility of one of the most fundamental glaciological metrics. Here, with a simple kinematic analysis, we argue why IS2SL is inherently a path-dependent metric and caution the paleo- and modern glaciology communities regarding its utility for data and model intercomparisons. [1] https://doi.org/10.5194/tc-14-2819-2020 [2] https://doi.org/10.5194/tc-14-833-2020