Abstract Thwaites Glacier is one of the fastest‐changing ice‐ocean systems in Antarctica. Basal melting beneath Thwaites' floating ice shelf, especially around pinning points and at the grounding line, sets the rate of ice loss and Thwaites' contribution to global sea‐level rise. The rate of basal melting is controlled by the transport of heat into and through the ice–ocean boundary layer toward the ice base. Here we present the first turbulence observations from the grounding line of Thwaites Eastern Ice Shelf. We demonstrate that contrary to expectations, the turbulence‐driven vertical flux of heat into the ice–ocean boundary layer is insufficient to sustain the basal melt rate. Instead, most of the heat required must be delivered by lateral fluxes driven by the large‐scale advective circulation. Lateral processes likely dominate beneath the most unstable warm‐cavity ice shelves, and thus must be fully incorporated into parameterizations of ice shelf basal melting.

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.

<p>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.  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.  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.  In Austral summer 2021-2022,  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.  The access hole allowed for ice, ocean, sediment, and environemental observations inside the channel.  We deployed the Icefin ROV, which is a novel platform that provides hydrographic, imaging, and sonar exploration in situ below the ice.  Here, we report the first Icefin observations from within the channel.  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.  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.  We discuss observations of boulder and sediment drape and suspended particulates in the water colum, and discuss implications for hydrological activity within the channel.</p>

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.

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.

Thwaites Glacier represents 15% of the ice discharge from the West Antarctic Ice Sheet and influences a wider catchment 1 – 3 . Because it is grounded below sea level 4 , 5 , Thwaites Glacier is thought to be susceptible to runaway retreat triggered at the grounding line (GL) at which the glacier reaches the ocean 6 , 7 . Recent ice-flow acceleration 2 , 8 and retreat of the ice front 8 – 10 and GL 11 , 12 indicate that ice loss will continue. The relative impacts of mechanisms underlying recent retreat are however uncertain. Here we show sustained GL retreat from at least 2011 to 2020 and resolve mechanisms of ice-shelf melt at the submetre scale. Our conclusions are based on observations of the Thwaites Eastern Ice Shelf (TEIS) from an underwater vehicle, extending from the GL to 3 km oceanward and from the ice–ocean interface to the sea floor. These observations show a rough ice base above a sea floor sloping upward towards the GL and an ocean cavity in which the warmest water exceeds 2 °C above freezing. Data closest to the ice base show that enhanced melting occurs along sloped surfaces that initiate near the GL and evolve into steep-sided terraces. This pronounced melting along steep ice faces, including in crevasses, produces stratification that suppresses melt along flat interfaces. These data imply that slope-dependent melting sculpts the ice base and acts as an important response to ocean warming.

Icefin is a custom designed remotely or autonomously operated vehicle (ROV/AUV) for sub-ice deployments in polar environments with a primary focus on modularity for deploying multiple payloads throughout a season to characterize the under-ice environment. Over the past six years the vehicle has undergone numerous design improvements to become a stable and robust platform. The current primary vehicle design was proven during the 2018 field campaign. With the success of that season, a second vehicle was built to accommodate two field campaigns in austral summer 2019–2020, wherein the vehicle dual Icefin vehicles were deployed through ~600m hot water drilled boreholes to investigate the grounding zones of Thwaites Glacier and the Ross Ice Shelf. Presented here is an overview of the engineering design updates that were incorporated from the 2017 season. Also presented are results and lessons learned from the 2019 deployments.

Here we present the design of a custom water sampling system for use on the underwater robot Icefin. The goals of this instrument are to collect discrete water samples in a compact form factor, operate in extreme underwater environments including high pressure and low temperature settings, and maintain a simple low-cost design. To achieve these objectives the system integrates a fluidic manifold, several compact solenoid pumps and valves, electronic controls, and an oil filled housing. A first-generation version of the water sampler was successfully tested on the underwater robot Icefin during ocean deployments in McMurdo Sound, Antarctica. A second-generation version of the system with a 3D printed manifold and improved capabilities has since been developed and undergone preliminary lab tests.

Forward-looking sonar is one of the most common and powerful instruments available for use in imaging underwater environments. Here, we explore the utility of these sonar sensors for mosaicking, mapping and topography reconstruction of areas of interest in our target under-ice and underwater environments. This is a difficult problem due to the noise in the sonar images as well as the changing appearance of objects when views from different points. Here we address the problem of sonar image alignment through sensor fusion with navigation instruments to provide an initial relative placement between sonar frames. We also discuss the use of such forward looking sonar sensors to build 3D point clouds of the ice topography.

Sampling systems on small underwater vehicles are needed to enable important aspects of ocean and polar science and represent a compelling design challenge. We describe the design of a system for in situ ice and sediment sampling aboard the Icefin vehicle. Small robotic riverbed sediment samplers designed to minimize the ballast weight by using novel methods of generating coring forces show that lightweight underwater vehicles can successfully collect solid samples, but their form factors make them ill-suited to be deployed in polar environments. We explore the design and development of a functional prototype of a manipulator arm with a sediment sampling end effector, investigate the design improvements required for the system to be deployed as a part of Icefin's payload using both tests from the prototype as well as simulations of expected dynamics, and provide recommendations for adjusting the system for ice coring. We find that a prototype of the system is able to penetrate test sediment up to 1.5 inches and verifies the model of the system that is used to iterate upon the design.

We present estimates of common actions associated with under-ice surveys and their energetic costs by examining data collected by two versions of the tethered, battery-operated unmanned underwater vehicle Icefin during 175 hours of operations under sea ice, glaciers and ice shelves. Our method and analysis yield design guidance for battery-operated unmanned underwater vehicles (UUVs) based on empirical evidence of the energy used to conduct a variety of oceanographic surveys under ice. Operator decisions are shown to significantly change the variance of a common action, allowing for energy reduction by modifying operator behavior, preventing a costly design change. The total energy released while performing common under-ice survey actions are shown to illustrate the most significant opportunities for improved efficiency in future vehicle designs.