Stratigraphy and Volumes of the Units Within the Massive Carbon Dioxide Ice Deposits of Mars
Ramina Alwarda, I. B. Smith
Abstract
Abstract The south polar layered deposits of Mars contain a massive CO 2 ice reservoir formed during periods of low planetary obliquity and partial atmospheric collapse. Within the reservoir are bounding layers (BLs) that are believed to consist entirely of water ice and modify CO 2 ice stability during periods of higher obliquity and insolation. Here we use three‐dimensional data from the Shallow Radar instrument to extend and update past mapping efforts of the reservoir in order to evaluate its internal structure and mass distribution. By mapping the entirety of each BL as two distinct reflectors, we provide individual volumetric calculations of the multiple CO 2 units for the first time (146, 1,472, and 5,493 km 3 ) and discover a new, smaller unit (12 km 3 ). Our volumetric measurements provide critical parameters to understanding past climatic states and climatological modeling, including the magnitude of atmospheric collapse and rebound over three separate events. We also provide updated thickness and areal extent measurements of BL1 (31 ± 5 m, 1,001 km 2 ), BL2 (32 ± 9 m, 5,415 km 2 ) and BL2+3 (42 ± 12 m, 4,232 km 2 ), with maximum thickness of ∼80 m. By mapping the entirety of the BLs, we find novel radar observations, attainable only in 3D, which support previous interpretations that both BL are composed of water ice. Our novel measurements will support climatological studies of Mars’ atmosphere in the past 500 kyr.