Sequestered glacial ice contribution to the global Martian water budget: Geometric constraints on the volume of remnant, midlatitude debris-covered glaciers

Glacial landforms on Mars, including concentric crater fill (CCF), lineated valley fill (LVF), and lobate debris aprons (LDA), were mapped between ~ ±30 and 50° latitude, and geometric constraints were placed on the volume of these deposits based on their topography and relationship with host topography (e.g., massifs, valleys, and craters). LDA deposits were found to have the largest volume (2.63 × 105 km3), followed by CCF deposits (8.75 × 104 km3) and LVF deposits (6.51 × 104 km3), for a total volume of 4.16 × 105 km3. The actual ice sequestered in these deposits is calculated depending on the estimated fraction of ice currently remaining in the deposits. We adopt end-member values of 30% (pore ice only) and 90% (relatively pure, debris-covered glacial ice). These volumes, 1.25 × 105 km3 and 3.74 × 105 km3 respectively, represent an equivalent global ice layer 0.9–2.6 m thick. On the basis of extensive recent local and regional analysis of these deposits indicating a debris-covered glacial origin, we favor the larger estimate. Taken together, these glacial landforms have an average thickness of ~450 m. The glacial deposition responsible for these features occurred or recurred during an extended period of the middle to late Amazonian, which implies that long-term climate conditions were sufficient to produce and preserve debris-covered glacial landforms on Mars.