Lake Joyce of the McMurdo Dry Valleys (MDV), Antarctica, contains an endemic copepod population (Diacyclops joycei) that has not been identified from apparently suitable habitats in nearby lakes. The absence of a known source for colonization has led to speculation that Lake Joyce may have acted as a refugium during periods when MDV climate was sufficiently arid that freshwater lakes were largely extirpated. However, Lake Joyce is canonically viewed as a young MDV lake due to its low salt content, challenging its refuge status. In this contribution, we present a new lake bathymetric model, water delta O-18 and delta H-2 values, and chloride budget to reassess lake history. Results are consistent with previous estimates of lake age but indicate that the full water column is in contact with Taylor Glacier. We propose that, due to its topographic setting, Lake Joyce migrates with the waxing and waning of Taylor Glacier through glacial cycles, episodically losing salts, leading to an erroneously young age estimate and providing a mechanism to maintain fresh conditions during Holocene climate changes. These mechanisms may have facilitated the maintenance of copepod populations through changes in regional hydrology that rendered other lakes inhospitable due to elevated salinity.

Field studies at terrestrial analogue sites represent an important contribution to the science of ocean worlds. The value of the science and technology investigations conducted at field analogue sites depends on the relevance of the analogue environment to the target ocean world. We accept that there are no perfect analogues for many of the unique environments represented by ocean worlds but suggest that a one-to-one matching of environmental characteristics and conditions is not crucial to the success or impact of the work. Instead, we must determine which processes and parameters are required to map directly to the target ocean world environment with high fidelity to address the science question. In this review paper, we discuss the outcomes of a workshop aimed at developing a new framework for evaluating the suitability of analogue field locations for ocean worlds research. Here we present a two-step approach to (a) identify the most crucial processes and parameters associated with a given science question and (b) assess the fidelity of these processes and parameters at a proposed field site to those expected for the target ocean world. We demonstrate this approach in a test case evaluating three types of ocean world analogue environments with respect to a science question. The consensus document presented here equips veteran and new investigators with valuable tools to better assess and justify their analogue site selections.

Beneath Antarctica's ice sheets, a little-observed network of liquid water connects vast landscapes and contributes to the motion of the overriding ice. When this subglacial water reaches the ocean cavity beneath ice shelves, it mixes with seawater, amplifying melt and in places forming deep channels in the base of the ice. Here we present observations from a hot-water-drilled borehole documenting subglacial water entering the ocean cavity at the grounding zone of Kamb Ice Stream and the Ross Ice Shelf. Our observations show that melt has removed approximately a third of the ice thickness, yet measurements reveal low rates of subglacial discharge in a turbid plume. Sediment cored from the channel floor shows larger discharge events occur and episodically deposit material from distinct geological domains. We quantify subglacial discharge and link our observations to the catchment upstream. We conclude that discrete discharge events are likely to dominate channel melt and sediment transport and result in the extensive ice-shelf features downstream of Kamb Ice Stream.

Melt beneath Antarctica’s large cold-cavity ice shelves remains a major source of uncertainty in ice sheet projections. Beneath these ice shelves melt is typically greatest both at the ice shelf front and at the grounding zone where ice first goes afloat. Grounding zone melt is thought to have a significant influence on ice flow across the grounding line, but can be difficult to estimate using remote sensing methods due to flexure of the overriding ice shelf. Added complexity in the grounding zone is caused by the thin water column, abundant basal crevassing, and the possible addition of subglacial fresh water draining from beneath the ice sheets. Here we present two independent estimates of basal melt from the ocean cavity of Kamb Ice Stream’s grounding zone, Ross Ice Shelf, West Antarctica. The first method uses repeat phase-sensitive radar observations to estimate melt in profiles from approximately 5 km seaward of the grounding line to approximately 3 km upstream of the grounding line. The second method uses an approximately 10-month long time series of oceanographic observations from a site 3.5 km seaward of the grounding line. Both methods are complemented by the high resolution observations provided by the Remotely Operated Vehicle (ROV) Icefin. The spatially distributed estimates show a more than tripling of melt rate within 5 km of the grounding line. The mooring derived melt rates demonstrate a melt-rate dependence on diurnal and spring-neap tidal currents. The average mooring melt rate more closely matches the radar-based estimates when a drag coefficient previously estimated using Icefin observations is used. Lastly we demonstrate an interesting correlation between mooring derived melt rates and ice shelf surface velocities obtained from Global Navigation Satellite System (GNSS) observations.

Melting from oceanic heat and basal lubrication from subglacial freshwater are fundamental elements of West Antarctic Ice Sheet mass balance that are poorly constrained. The ice streams feeding the Ross Ice Shelf grounding line periodically start and stall over decadal to century timescales due to shifts in these forcings. Here, we present in situ hydrographic measurements, noble gas abundances, and helium isotope ratios from a large subglacial channel melted into the base of stagnant Kamb Ice Stream. These data identify an outflowing plume containing subglacial freshwater admixture from upstream volcanic activity and anomalously warm inflowing seawater containing Circumpolar Deep Water from the Ross Sea, with oceanic heat delivery outpacing that from volcanism. Our results directly quantify both variables that affect the mass balance of the Ross Ice Shelf’s sensitive interconnected ice streams and highlight the vulnerability of this region of West Antarctica to increased forcing from a warming climate.

Unoccupied aircraft systems (UAS) technology on Earth has become increasingly prevalent and accessible, and for extraterrestrial applications, the Ingenuity helicopter has proven the viability of flight on Mars. Advantages provided by UAS on both Earth and Mars include faster and broader access to traditionally difficult-to-reach terrain. Here, we demonstrate the use of UAS-based sample collection and retrieval systems for applications on Earth and Mars, which we tested in Martian analog sites in the Holuhraun region of Iceland, at the Galena Creek rock glacier in Wyoming, and around the Eastern Sierra in California. The two sampling systems include a Drill Sampler and a Scoop Sampler, both coupled to commercial off-the-shelf drones. The Drill Sampler is a lightweight rotary-percussive coring drill with powder collection capability, compliantly mounted to the UAS to allow for drilling into a variety of different materials and uneven terrain. The Scoop Sampler uses modular interchangeable scoops for collecting and retrieving different types of samples. These sampling systems collected a suite of various samples, including rock cores, bulk samples, and replica Mars sample tubes. By collecting various samples in diverse terrains, we show that this technology enables adaptable sampling and sample transport for both earthbound and future planetary exploration missions.

At present, considerable uncertainty surrounds the details of how Earth’s ice sheets interact with the surrounding ocean. This inhibits the reliability of future sea level rise projections from ice sheet models and highlights a need to better constrain ice-ocean interactions with in situ observations. Here, we present detailed ice and ocean data from beneath Thwaites Eastern Ice Shelf, Antarctica, collected with the underwater vehicle Icefin as part of the ITGC MELT project. The observations are a subset of the full data set that focus on the ice-ocean interactions within one 4-m-tall and 200-m-wide terrace formation in the ice base. We present ocean conditions in the terrace from 18 hydrographic profiles that reached within 1 cm of the ice along the feature’s flat roof and 13 cm from its steep sidewall. The ocean observations depict highly stable near-ice ocean stratification within 1 m of the terrace roof that break down near its sidewall, allowing warmer and more saline water to contact the ice there. The ocean observations are combined with ice base elevations and scaled morphological melt patterns in the ice to understand the dominant mechanisms driving ice-ocean interactions within this feature. We then input these data into the three-equation melt parameterization to estimate spatial variability in melt rates within these topographic features. We test various parameterizations for ocean heat flux into the flat and sloped ice surfaces, and compare the results to melt rates sampled along a nearby terrace sidewall and roof with a phase sensitive radar. This work in progress aims to better understand how ocean conditions interact with ice slope on small scales to drive variable melting in warm, highly stratified environments, with hopes of refining existing parameterizations of this process. We expect regions beneath much of the ice shelves occupying West Antarctica to interact similarly with the underlying ocean to what we observe beneath Thwaites. Hence, our observations hold relevance for how ice sheet models parameterize ocean-driven melting in this type of melt-driven regime.

Geological investigations planned for the Europa Clipper mission will examine the formation, evolution, and expression of geomorphic structures found on the surface. Understanding geologic features, their formation, and any recent activity are key inputs in constraining Europa’s potential for habitability. In addition to providing information about the moon’s habitability, the geologic study of Europa is compelling in and of itself. Here we provide a high-level, cross-instrument, and cross-discipline overview of the geologic investigations planned within the Europa Clipper mission. Europa’s fascinating collection of ice-focused geology provides an unparalleled opportunity to investigate the dynamics of icy shells, ice-ocean exchange processes, and global-scale tectonic and tidal stresses. We present an overview of what is currently known about the geology of Europa, from global to local scales, highlighting outstanding issues and open questions, and detailing how the Europa Clipper mission will address them. We describe the mission’s strategy for searching for and characterizing current activity in the form of possible active plumes, thermal anomalies, evidence for surface changes, and extremely fresh surface exposures. The complementary and synergistic nature of the data sets from the various instruments and their integration will be key to significantly advancing our understanding of Europa’s geology.

The freezing point of water is negatively dependent on pressure; therefore in any ocean without external forcing it is warmest at the surface and grows colder with depth. Below floating ice on Earth (e.g., ice shelves or sea ice), this pressure dependence combines with gradients in the ice draft to drive an ice redistribution process termed the "ice pump": submerged ice melts, upwells, and then refreezes at shallower depths. Ice pumping is an exchange process between the ocean and overhead ice that results in unique ice compositions and textures and influences the distribution of sub-ice habitats on Earth. Here, we scale recent observations from Earth's ice shelves to planetary conditions and find that ice pumping is expected for a wide range of possible sub-ice shell pressures and salinity at other ocean worlds such as Europa and Enceladus. We show how ice pumping would affect hypothetical basal ice shell topography and ice thickness under varying ocean conditions and demonstrate how remote sensing of the ice shell draft can be used to estimate temperature gradients in the upper ocean ahead of in situ exploration. For example, the approximately 22 km gradient observed in Enceladus' ice shell draft between the south pole and the equator suggests a temperature differential of 0.18 K at the base of the ice shell. These concepts can extend the interpretation of observations from upcoming ocean world missions, and link ice shell topography to ice-ocean material exchange processes that may prove important to overall ocean world habitability. The freezing point of water depends on pressure. As pressure increases, the freezing point decreases, which can influence the melting or freezing of ice in an ocean. A helpful way to conceptualize this dependency is to recall that water expands as it freezes. As pressure increases, this expansion requires more work to displace the higher pressure surroundings, so the water must be even colder to freeze-a decrease in the freezing point. If ice is submerged, the deeper ice where the freezing point is colder can melt faster. This forms freshened meltwater that may rise to shallower depths where it is now colder than the shallower, lower pressure freezing point and can refreeze underwater. This process is referred to as an "ice pump", because it acts to equilibrate topography in submerged ice. In ice-covered oceans on Earth, the ice pump is an important process that influences the composition and texture of the ice, and therefore the sub-ice ecosystems. Here, we find that ice pumping is also likely at other ocean worlds in our solar system where it may similarly influence potential sub-ice ecosystems and show how observations of planetary ice shell thicknesses can be used to bound ocean conditions. When ice is submerged, a melting and freezing exchange process termed the "ice pump" can affect ice composition, texture, and thickness We find that ice pumping is likely beneath the ice shells of several ocean worlds in our solar system The ice pump concept enables inversion between ocean world ice shell thickness and ice-ocean interface temperature ranges

Sediment accumulating beneath floating ice contains a record of ice dynamics in polar regions where in situ observations are rare. In 2019 a hole was melted through a 590m-thick region of the Ross Ice Shelf similar to 5 km seawards of the Kamb Ice Stream (KIS) grounding line (82.7841 degrees S, 155.2626 degrees W) to access the seafloor. Imagery from a remotely operated vehicle (ROV, Icefin) shows ocean current-generated ripples likely formed by tidal flow parallel to the grounding line (GL). Observed current speeds <0.15 m s(-1) suggest these bedforms may be relict. Larger, dm-scale, 'furrows' parallel to the former direction of KIS flow may relate to past grounding line processes. A 0.49 m-long gravity core collected from the seafloor contains weakly stratified diamicton. The sediment matrix comprises variable mixtures of reworked Tertiary biogenic silica, predominantly diatoms, and arkose material. Sediment epsilon(Nd) values of similar to 7 are consistent with derivation from the WAIS, as is the U-Pb age distribution and modelled late Holocene ice flows. Ramped pyrolysis C-14 analysis shows all fractions are either >30 ka or C-14 dead. By contrast, Pb-210-210 activity of >30 Bq Kg(-1) indicates deposition within the last 120 years. The combination of features suggests rapid rainout deposition from melting of a sediment-laden basal debris layer as the GL retreated, followed by some reworking by ocean currents and little modern accumulation. Although Tertiary diatoms are abundant, unambiguously Late Quaternary forms are absent and we speculate on the implications for Ross Ice Shelf stability. [239 wds]

A remotely-operated underwater vehicle was used to map the ice, ocean, and seafloor conditions near the point where the floating Ross Ice Shelf meets the seafloor, also known as the grounding line. The study identified refreezing crevasses and geomorphological signatures of past grounding line retreat.

Several worlds in our solar system are thought to hold oceans of liquid water beneath their frozen surfaces. These subsurface ice and ocean environments are promising targets in the search for life beyond Earth, but they also present significant new technical challenges to planetary exploration. With a focus on Jupiter's moon Europa, here we (1) identify major benefits and challenges to subsurface ocean world science, (2) provide a multidisciplinary survey of relevant sample handling and life detection technologies, and (3) integrate those perspectives into the Subsurface Science and Search for Life in Ocean Worlds (SSSLOW) concept payload. We discuss scientific goals across three complementary categories: (1) search for life, (2) assess habitability, and (3) investigate geological processes. Major mission challenges considered include submerged operation in high-pressure environments, the need to sample fluids with a range of possible chemical conditions, and detection of biosignatures at low concentrations. The SSSLOW addresses these issues by tightly integrated instrumentation and sample handling systems to enable sequential, complementary measurements while prioritizing preservation of sample context. In this work, we leverage techniques and technologies across several fields to demonstrate a path toward future subsurface exploration and life detection in ice and ocean worlds.

Abstract While liquid environments with high salt content are of broad interest to the Earth and Planetary Science communities, instruments face challenges in detecting organics in hypersaline samples due to the effects of salts. Therefore, technology to desalt samples before analysis by these instruments would be enabling for liquid sampling on missions to Mars or ocean worlds. Electrodialysis (ED) removes salt from aqueous solutions by applying an electric potential across a series of ion‐selective membranes, and is demonstrated to retain a significant percentage of dissolved organic molecules (DOM) in marine samples. However, current electrodialysis systems used for DOM recovery are too large for deployment on missions or for use in terrestrial fieldwork. Here, we present the design and evaluation of the Miniature Robotic Electrodialysis (MR ED) system, which is approximately 1/20th the size of heritage instruments and processes as little as 50 mL of sample at a time. We present tests of the instrument efficiency and DOM recovery using lab‐created solutions as well as natural samples taken from an estuary of the Skidaway River (Savannah, GA) (Verity, 2002) and from South Bay Saltworks (San Diego, CA) (Roseman & Watry, 2008; Survey, 2011). Our results show that the MR ED system removed 97%–99% of the salts in most samples, with an average DOC recovery range from 53% to 77%, achieving similar capability to tabletop instruments. This work both demonstrates MR ED as a possible field instrument and increases the technology readiness level of miniaturized electrodialysis systems for future missions.

Thwaites Glacier is one of the fastest-changing ice–ocean systems in Antarctica 1 – 3 . Much of the ice sheet within the catchment of Thwaites Glacier is grounded below sea level on bedrock that deepens inland 4 , making it susceptible to rapid and irreversible ice loss that could raise the global sea level by more than half a metre 2 , 3 , 5 . The rate and extent of ice loss, and whether it proceeds irreversibly, are set by the ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat 3 , 6 , both of which are largely unknown. Here we show—using observations from a hot-water-drilled access hole—that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, low current speeds and strong density stratification in the ice–ocean boundary layer actively restrict the vertical mixing of heat towards the ice base 7 , 8 , resulting in strongly suppressed basal melting. Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates.

&lt;p&gt;Kamb Ice Stream (KIS) is one of the largest tributaries to the Ross Ice Shelf, grounded near the southermost edge of the massive ice shelf.&amp;#160; Stagnant for some 150 years, the rerouting of subglacial water beneath the ice stream and others in the region is likely critical to the stagnation of the ice stream, as well as present and future dynamics.&amp;#160; As part of the Antarctic New Zealand-led Antarctic Science Platform, our NSF- and NASA- funded team was able to participate in two field seasons accessing below KIS.&amp;#160; In Austral summer 2021-2022,&amp;#160; a hot water drilled borehole was made through the ice and into the major subglaciall channel upstream of the grounding line that carries subglacial water in to the ocean.&amp;#160; The access hole allowed for ice, ocean, sediment, and environemental observations inside the channel.&amp;#160; We deployed the Icefin ROV, which is a novel platform that provides hydrographic, imaging, and sonar exploration in situ below the ice.&amp;#160; Here, we report the first Icefin observations from within the channel.&amp;#160; We report channel geometry, ice-ocean interactions at the top and side walls of the channel, and sonar and imaging data of the sediment along a 500m mission extending upstream of the borehole.&amp;#160; In particular, we report bathymetric observations of the bed of the channel, which varied by 10s of me in width over the mission, and into which a small, meandering ~4m deep channel was incised into the sediments.&amp;#160; We discuss observations of boulder and sediment drape and suspended particulates in the water colum, and discuss implications for hydrological activity within the channel.&lt;/p&gt;

Ice streams flowing into Ross Ice Shelf are presently responsible for around 10% of the mass flux from West Antarctica, with the noteworthy exception of Kamb Ice Stream, which stagnated in the late 1800s. The subsequent reduction in ice supply led to grounding-line retreat at the coastal margin where Kamb transitions into the floating Ross Ice Shelf. Grounding-line migration is linked to broader changes in ice-sheet mass balance and sea level, but our understanding of related ice, ocean and seafloor interactions is limited by the difficulty in accessing these remote regions. Here we report in situ observations from an underwater vehicle deployed at Kamb that show how fine-scale variability in ice and ocean structure combine to influence a diversity of ice-ocean interactions. We found a stratified water column within a tenth of a degree of freezing at the ice base and mapped basal crevasses with supercooled water and active marine ice formation. At the seafloor, we interpret parallel ridges as crevasse impressions left as the ice lifted off during grounding-line retreat. These observations from a recently ungrounded sub-shelf environment illuminate both the geomorphological signatures of past grounding-line retreat and the fine-scale sensitivity of ongoing ice-ocean interactions to ice topography.

The Galileo mission to Jupiter revealed that Europa is an ocean world. The Galileo magnetometer experiment in particular provided strong evidence for a salty subsurface ocean beneath the ice shell, likely in contact with the rocky core. Within the ice shell and ocean, a number of tectonic and geodynamic processes may operate today or have operated at some point in the past, including solid ice convection, diapirism, subsumption, and interstitial lake formation. The science objectives of the Europa Clipper mission include the characterization of Europa’s interior; confirmation of the presence of a subsurface ocean; identification of constraints on the depth to this ocean, and on its salinity and thickness; and determination of processes of material exchange between the surface, ice shell, and ocean. Three broad categories of investigation are planned to interrogate different aspects of the subsurface structure and properties of the ice shell and ocean: magnetic induction, subsurface radar sounding, and tidal deformation. These investigations are supplemented by several auxiliary measurements. Alone, each of these investigations will reveal unique information. Together, the synergy between these investigations will expose the secrets of the Europan interior in unprecedented detail, an essential step in evaluating the habitability of this ocean world.

Ocean conditions near the grounding zones of Antarctica's ice shelves play a key role in controlling the outflow and mass balance of the ice sheet. However, ocean observations in these regions are largely absent. Here, we present a detailed spatial survey collected with an underwater vehicle in a basal crevasse located in the ocean cavity at the Ross Ice Shelf grounding zone. The observations depict fine-scale variability in ocean forcing that drives asymmetric melting along the lower crevasse sidewalls and freezing in the upper reaches of the crevasse. Freshwater release from melting at depth and salt rejection from freezing above drives an overturning circulation. This vertical circulation pattern overlays a dominant throughflow jet, which funnels water parallel to the coastline, orthogonal to the direction of tidal currents. Importantly, these data reveal that basal crevasses influence ocean circulation and mixing at ice shelf grounding zones to an extent previously unknown.

The habitability of Europa is a property within a system, which is driven by a multitude of physical and chemical processes and is defined by many interdependent parameters, so that its full characterization requires collaborative investigation. To explore Europa as an integrated system to yield a complete picture of its habitability, the Europa Clipper mission has three primary science objectives: (1) characterize the ice shell and ocean including their heterogeneity, properties, and the nature of surface-ice-ocean exchange; (2) characterize Europa's composition including any non-ice materials on the surface and in the atmosphere, and any carbon-containing compounds; and (3) characterize Europa's geology including surface features and localities of high science interest. The mission will also address several cross-cutting science topics including the search for any current or recent activity in the form of thermal anomalies and plumes, performing geodetic and radiation measurements, and assessing high-resolution, co-located observations at select sites to provide reconnaissance for a potential future landed mission. Synthesizing the mission's science measurements, as well as incorporating remote observations by Earth-based observatories, the James Webb Space Telescope, and other space-based resources, to constrain Europa's habitability, is a complex task and is guided by the mission's Habitability Assessment Board (HAB).