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Recent results from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument have been interpreted as evidence of subsurface brine pooled beneath 1.3 km‐thick South Polar Layered Deposit (SPLD). This interpretation is based on the assumption that the regionally high strength of MARSIS radar reflections from the base of the ice cap is due to a strong contrast in dielectric permittivity across the basal interface. Here, we demonstrate that the high‐power reflections could instead be the result of a contrast in electric conductivity. While not explicitly excluding a liquid brine, our results open new potential explanations for the observed strong radar reflections, some of which do not require liquid brine beneath SPLD. Potential basal materials with suitably high conductivity include clays, metal‐bearing minerals, or saline ice.

 

Abstract. Since the 1960s, a deep groundwater system in Wright Valley, Antarctica, has been the hypothesized source of brines to hypersaline Don Juan Pond and Lake Vanda, both of which are rich in calcium and chloride. Modeling studies do not support other possible mechanisms, such as evaporative processes, that could have led to the current suite of ions present in both waterbodies. In 2011 and 2018, an airborne electromagnetic survey was flown over Wright Valley to map subsurface resistivity (down to 600 m) in exploration of liquid water. The surveys revealed widespread unfrozen brine in the subsurface near Lake Vanda, Don Juan Pond, and the North Fork of Wright Valley. While our geophysical survey can neither confirm nor deny deep groundwater connectivity between Lake Vanda and Don Juan Pond, it does point to the potential for deep valley-wide brine, likely within the Ferrar Dolerite formation. 

SUMMARY Airborne electromagnetics (EM) is a geophysical tool well suited to mapping glacial and hydrogeological structures in polar environments. This non-invasive method offers significant spatial coverage without requiring access to the ground surface, enabling the mapping of geological units to hundreds of metres depth over highly varied terrain. This method shows great potential for large-scale surveys in polar environments, as common targets such as permafrost, ice and brine-rich groundwater systems in these settings can be easily differentiated because of their significant contrasts in electrical properties. This potential was highlighted in a 2011 airborne EM survey in the McMurdo Dry Valleys that mapped the existence of a large-scale regional groundwater system in Taylor Valley. A more comprehensive airborne EM survey was flown in November 2018 to broadly map potential groundwater systems throughout the region. Data collected in this survey displayed significant perturbations from a process called induced polarization (IP), an effect that can greatly limit or prevent traditional EM workflows from producing reliable geological interpretations. Here, we present several examples of observed IP signatures over a range of conditions and detail how workflows explicitly designed to handle IP effects can produce reliable geological interpretations and data fits in these situations. Future polar EM surveys can be expected to encounter strong IP effects given the likely presence of geological materials (e.g. ice and permafrost) that can accentuate the influence of IP. 

Abstract. Previous studies of the lakes of the McMurdo Dry Valleys haveattempted to constrain lake level history, and results suggest the lakeshave undergone hundreds of meters of lake level change within the last20 000 years. Past studies have utilized the interpretation of geologicdeposits, lake chemistry, and ice sheet history to deduce lake levelhistory; however a substantial amount of disagreement remains between thefindings, indicating a need for further investigation using new techniques.This study utilizes a regional airborne resistivity survey to provide novelinsight into the paleohydrology of the region. Mean resistivity mapsrevealed an extensive brine beneath the Lake Fryxell basin, which isinterpreted as a legacy groundwater signal from higher lake levels in thepast. Resistivity data suggest that active permafrost formation has beenongoing since the onset of lake drainage and that as recently as 1500–4000 years BP, lake levels were over 60 m higher than present. This coincideswith a warmer-than-modern paleoclimate throughout the Holocene inferred bythe nearby Taylor Dome ice core record. Our results indicate Mid to LateHolocene lake level high stands, which runs counter to previous researchfinding a colder and drier era with little hydrologic activity throughoutthe last 5000 years. 

Abstract. We have examined a general expression giving the specularreflection coefficient for a radar wave approaching a reflecting interfacewith normal incidence. The reflecting interface separates two homogeneousisotropic media, the properties of which are fully described by three scalarquantities: dielectric permittivity, magnetic permeability, and electricalconductivity. The derived relationship indicates that electricalconductivity should not be neglected a priori in glaciological investigations ofsubglacial materials and in ground-penetrating radar (GPR) studies of saturated sediments and bedrock,even at the high end of typical linear radar frequencies used in suchinvestigations (e.g., 100–400 MHz). Our own experience in resistivitysurveying in Antarctica, combined with a literature review, suggests that awide range of geologic materials can have electrical conductivity that ishigh enough to significantly impact the value of radar reflectivity.Furthermore, we have given two examples of prior studies in which inclusionof electrical conductivity in calculation of the radar bed reflectivity mayprovide an explanation for results that may be considered surprising if theimpact of electrical conductivity on radar reflection is neglected. Thecommonly made assumption that only dielectric permittivity of the two medianeeds to be considered in interpretation of radar reflectivity can lead toerroneous conclusions. 

The Southern Ocean receives limited liquid surface water input from the Antarctic continent. It has been speculated, however, that significant liquid water may flow from beneath the Antarctic Ice Sheet, and that this subglacial flow carries that water along with dissolved nutrients to the coast. The delivery of solutes, particularly limiting nutrients like bioavailable iron, to the Southern Ocean may contribute to ecosystem processes including primary productivity. Using a helicopter-borne time domain electromagnetic survey along the coastal margins of the McMurdo Dry Valleys region of Southern Victoria Land, Antarctica, we detected subsurface connections between inland lakes, aquifers, and subglacial waters. These waters, which appear as electrically conductive anomalies, are saline and may contain high concentrations of biologically important ions, including iron and silica. Local hydraulic gradients may drive these waters to the coast, where we postulate they emerge as submarine groundwater discharge. This high latitude groundwater system, imaged regionally in the McMurdo Dry Valleys, may be representative of a broader system of Antarctic submarine groundwater discharge that fertilizes the Southern Ocean. In total, it has the potential to deliver tens of gigagrams of bioavailable Fe and Si to the coastal zone.