TY - JOUR
T1 - Radar Reflectivity as a Proxy for the Dust Content of Individual Layers in the Martian North Polar Layered Deposits
AU - Lalich, D. E.
AU - Holt, J. W.
AU - Smith, I. B.
N1 - Funding Information:
We would like to thank the SHARAD team as well as the Italian Space Agency (ASI) who provided the SHARAD instrument for the MRO mission. This work was supported by NASA grant NNX15AM52G, the NESSF fellowship program, and the Jackson School of Geosciences. All data used in this work are available from NASA's Planetary Data System (PDS). The SHARAD reference chirp can be downloaded from the PDS (http://pds-geosciences.wustl.edu/mro/mro-m-sharad-4-rdr-v1/mrosh_1003/calib/). Files containing the orbit number, latitude, and longitude for each observation used in this work are available as supplementary information.
PY - 2019
Y1 - 2019
N2 - The stratigraphy of the north polar layered deposits (NPLD) of Mars is believed to contain a climate record of the recent Amazonian period. However, full utilization of this record is difficult without detailed information regarding the physical properties of the constituent layers. Here we present a method for determining the fractional dust content of individual layers using a combination of orbital radar reflectivity measurements and physical modeling. We apply this method to the upper 500 m of the NPLD at 10 study sites and compare the results to a cap-wide radar-mapped surface. Our results show that reflectivity can vary drastically both geographically and with depth, a result we attribute to changing dust content, though the impact of variable layer thickness cannot be totally discounted. These findings imply large-scale regional patterns in ice and dust accumulation do not remain consistent through time. We also find that current models of Mars's dust cycle and polar ice accumulation consistently underpredict the dust content of layers, indicating that our understanding of dust transport, dust sequestration, or dust preservation remains incomplete. Comparisons of study sites on the NPLD also show that some locations contain fewer radar reflectors than others, meaning they may contain a less complete record of the planet's recent paleoclimate, and any future efforts to use the polar layered deposits as a climate proxy, including in situ measurements, should take this into account by choosing study sites wisely.
AB - The stratigraphy of the north polar layered deposits (NPLD) of Mars is believed to contain a climate record of the recent Amazonian period. However, full utilization of this record is difficult without detailed information regarding the physical properties of the constituent layers. Here we present a method for determining the fractional dust content of individual layers using a combination of orbital radar reflectivity measurements and physical modeling. We apply this method to the upper 500 m of the NPLD at 10 study sites and compare the results to a cap-wide radar-mapped surface. Our results show that reflectivity can vary drastically both geographically and with depth, a result we attribute to changing dust content, though the impact of variable layer thickness cannot be totally discounted. These findings imply large-scale regional patterns in ice and dust accumulation do not remain consistent through time. We also find that current models of Mars's dust cycle and polar ice accumulation consistently underpredict the dust content of layers, indicating that our understanding of dust transport, dust sequestration, or dust preservation remains incomplete. Comparisons of study sites on the NPLD also show that some locations contain fewer radar reflectors than others, meaning they may contain a less complete record of the planet's recent paleoclimate, and any future efforts to use the polar layered deposits as a climate proxy, including in situ measurements, should take this into account by choosing study sites wisely.
KW - Mars
KW - climate
KW - ice
KW - radar
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U2 - 10.1029/2018JE005787
DO - 10.1029/2018JE005787
M3 - Article
AN - SCOPUS:85068522341
VL - 124
SP - 1690
EP - 1703
JO - Journal of Geophysical Research: Planets
JF - Journal of Geophysical Research: Planets
SN - 2169-9097
IS - 7
ER -