Winter thermohaline evolution along andbelow the Ross Ice Shelf

Observations beneath ice-covered oceans and within ice-shelf cavities are central to understanding the ocean-ice interactions that influence ice-shelf stability, contribute to global sea-level change, and shape large-scale ocean circulation patterns. However, direct observations in these regions, particularly those capturing wintertime conditions, remain scarce due to the logistical challenges posed by persistent ice cover. Emerging autonomous technologies and new applications now offer opportunities to address these observational gaps.
Since 2020, we have deployed 20 unconventionally programmed Argo floats in key regions of the Ross Sea, including the Terra Nova Bay and Ross Ice Shelf polynyas, the critically under-sampled Eastern Gate, and along the Ross Ice Shelf front. These floats provide year-round thermohaline and biochemical measurements, which, among other capabilities, allow for the quantification of water mass transformations, sub-ice dynamics, and key processes such as the production of High Salinity Shelf Water, a precursor to Antarctic Bottom Water. This represents a significant advancement, as previous studies have largely relied on summer ship-based or satellite-derived observations, which fail to capture the full seasonal cycle.
Futhermore, with measurements from three Argo floats operating for several months beneath the Ross Ice Shelf, we directly observed and quantified processes that had previously only been hypothesized. These include the intrusion of seasonally warmed Antarctic Surface Water, identified as a primary driver of frontal and basal melting, along with its associated effects on ocean heat content and basal melt rates, as well as the outflow of Ice Shelf Water, the coldest ocean water in the world.

Building on the insights gained over the past 4 years, we argue that broadening the deployment of grounded-mode Argo floats across Antarctica can provide a unique understanding of ocean-ice interactions. By enabling continuous, autonomous measurements — even in winter and under ice — this approach can improve our capacity to quantify key processes, such as the lateral and vertical extent of shelf water production and the mechanisms driving basal melt. Our results demonstrate that Argo floats offer direct evidence of how heat absorbed at the surface is transported into ice-shelf cavities, contributing to basal melting and reshaping our understanding of water mass formation processes in coastal polynyas. Expanding the float network would enhance our ability to detect interannual variability, characterize longer-term trends, and reduce uncertainties in ice-shelf and sea-level projections, ultimately supporting more accurate climate model predictions for these critical polar environments.