In a breakthrough study revealing the complex and dynamic nature of Antarctica’s grounding zones, researchers have uncovered an environment profoundly shaped by episodic water flows beneath the West Antarctic Ice Sheet. This investigation into one of the most remote and enigmatic parts of our planet employed innovative borehole drilling and cutting-edge oceanographic profiling, offering an unprecedented glimpse into subglacial hydrology and the intricate channel systems sculpting the ice-ocean interface.
The research team drilled a borehole at precise coordinates deep within the Antarctic ice, reaching a location at 82.47048° S and 152.29145° W. The borehole was meticulously created using a high-pressure hot water lance system that melted through the ice, allowing direct access to the sub-ice environment. Operational challenges in this process included a blockage encountered during drilling, which necessitated repositioning the borehole 10 meters downstream. This adjustment did not deter the extensive science program, which encompassed multiple operational cycles combining data collection with cautious reaming procedures to maintain borehole integrity over approximately two weeks between late December 2021 and mid-January 2022.
Profiling within the borehole employed a rotating 500 kHz altimeter capable of mapping the subterranean channel’s dimensions with sub-centimeter precision. By tilting and slowly rotating this instrument as it descended, the researchers constructed a detailed cross-sectional model of the grounding-zone channel, capturing its roof, walls, and floor topography. A noted region of uncertainty existed in a lower corner, where altimeter returns were sparse, but this did not meaningfully impact the team’s quantification of subglacial discharge or meltwater fluxes due to minimal water mass contribution from that area.
Crucial to the study was the velocity profiling of water masses inside the channel. Utilizing a Nortek Aquadop current meter and an RBR Duet sensor package, the team recorded water velocity, temperature, and pressure. While some upper channel layers exhibited backscatter interference and noise from the altimeter, leading to variable readings, the group mitigated this by focusing on data from deeper in the channel and through deployment of an autonomous mooring array positioned at strategic heights above the channel floor. These instruments sampled current velocities over extended durations, providing valuable time-series data essential for understanding the dynamics of subglacial water flow.
To complement these measurements, hydrographic profiling combined conductivity, temperature, salinity, and turbidity data. The sensors underwent rigorous data processing to correct for atmospheric pressure fluctuations, tidal influences, and equipment artifacts such as icing and or instrument equilibration effects. Their composite mean profiles, binned at fine vertical intervals, afforded an accurate depiction of the water column’s thermohaline structure within the channel. Importantly, the team converted practical salinity and in situ temperatures using TEOS-10 standards, an approach that enables robust comparisons and is currently state-of-the-art in oceanographic measurements.
A key insight arose from partitioning the water masses within the channel through a three-member mixing model. This model assumed the presence of High-Salinity Shelf Water (HSSW), glacial meltwater (GMW), and subglacial discharge water (SGW), each characterized by distinct temperature and salinity signatures. The method used simultaneous equations relating measured conservative temperatures and absolute salinities allowed for estimation of the proportion of each water mass vertically throughout the channel. These proportions, coupled with velocity measurements, permitted the team to derive fluxes, shedding light on the dynamic water transport processes beneath the grounding zone.
Beyond fluid dynamics, sediment core analysis revealed further dimensions of the grounding-zone environment. The team recovered a half-meter sediment core through the borehole, preserving it under controlled temperature conditions. High-resolution CT scans of the core, combined with hyperspectral imaging, provided detailed density profiles and surface characterizations critical for reconstructing depositional histories. Grain-size analyses following oxidation treatments to remove organic materials allowed further categorization of sediment properties, which carry signatures of past ice sheet and ocean interactions.
Isotopic investigations into neodymium (Nd) and strontium (Sr) ratios in sediment fractions added an invaluable geochemical layer to the study. Using ion-exchange chromatography and highly precise mass spectrometry, the researchers obtained isotope ratios corrected for instrumental biases and interferences. Nd isotope values, expressed in epsilon notation relative to chondritic uniform reservoirs, and Sr isotopes, compared against global standards, act as tracers for sediment provenance and processes affecting sediment deposition beneath the ice.
The study also illuminated the ancient timeline of sediment deposition within the system. Through diatom assemblage analysis, particularly from the lowermost sediment unit, the researchers pinpointed a Miocene age of roughly 18 million years. Diagnostic ranges of certain diatom species enabled this temporal placement, revealing a long geological history preserved in the grounding-zone sediments and reflecting ancient conditions within Antarctica’s subsurface environment.
To understand the pathways of subglacial water feeding into the grounding-zone channel, the team employed sophisticated subglacial routing and catchment modeling techniques. Harnessing hydropotential gradients and Monte Carlo-based stochastic methods, they simulated numerous realizations of bed and surface topography, flotation fractions, and meltwater fluxes. Data inputs for these models derived from high-resolution digital elevation models and bed mapping datasets, ensuring realistic spatial representation. The results identified probable hydrological catchments upstream of an 18-kilometer grounding-zone segment, with a quantified flux crossing this portion, although minor mismatches in modeled versus observed channel positions highlighted model limitations.
The dynamic activity of subglacial lakes in the vicinity further contextualizes the episodic water flows shaping the environment. Satellite altimetry data from CryoSat-2 and ICESat-2 missions were analyzed to detect surface elevation changes indicative of subglacial lake filling and draining events between 2010 and 2023. These observations demonstrated periods of active lake dynamics, followed by phases of inactivity, reflecting subtle but critical hydrospatial processes beneath the ice sheet.
Moreover, volume change time series derived from these elevation records offered estimates of ice volume displacement triggered by subglacial lake activity. This approach accounted for regional background trends and applied assumptions of a one-to-one volume exchange between ice and water displacement. While acknowledging potential oversimplifications in this method within slow-flowing ice streams like the Kamb Ice Stream trunk, these results provide vital constraints on subglacial hydrological variability.
Complementing these in situ and remote sensing efforts, airborne swath radar imaging delivered expansive spatial context. Conducted in late 2013, the radar array mapped basal topography across a swath approximately one kilometer wide, with fine spatial resolution along and across flight tracks. The method utilized coherent radar depth sounding and cross-track processing to delineate basal features, contributing to a multiscale understanding of channel morphology and grounding-line topography.
Together, these integrated geophysical, oceanographic, sedimentological, geochemical, and modeling approaches paint a comprehensive picture of a grounding-zone environment profoundly sculpted by episodic, variable water fluxes. This intricate interplay of subglacial hydrology and ice dynamics carries substantial implications for ice-sheet stability, ocean circulation, and future Antarctic contributions to sea-level rise. As researchers continue to untangle the mysteries of these hidden realms, the insights afforded by such cutting-edge investigations pave the way for improved predictive models and a deeper grasp of Earth’s changing polar frontiers.
Subject of Research:
Subglacial hydrology and grounding-zone channel dynamics beneath the West Antarctic Ice Sheet.
Article Title:
A West Antarctic grounding-zone environment shaped by episodic water flow.
Article References:
Horgan, H.J., Stewart, C., Stevens, C. et al. A West Antarctic grounding-zone environment shaped by episodic water flow. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01687-3
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