Hydrographic Variability in the Central Ross Ice Shelf Cavity and the Implications for Ocean Circulation

Abstract The ocean beneath ice shelves plays a critical role in their evolution and resilience. Despite this, direct observations of circulation within ice shelf cavities remain scarce. Here, we examine 4.5 years of moored hydrographic data (2018–2022) from the HWD2 borehole, which represent the first multi‐year measurements of currents, temperature, and conductivity from the central Ross Ice Shelf cavity. The data set resolves distinct temporal variability across the water column. While the basal meltwater layer circulates differently from the deeper layers, the upper mid–water column is characterized by complex thermohaline structure that represents intrusions of supercooled water driven by sub‐seasonal processes rather than the previously hypothesized spring–neap tidal cycle. These intrusions also exhibit a seasonal cycle. In contrast, the lower mid‐depth region more closely reflects the open ocean signal. Multi‐year records reveal inter‐annual variability, highlighted by enhanced melting and refreezing from September to November 2019. Observations suggest that the enhanced melting and refreezing in late 2019 were influenced by strong Ross Ice Shelf polynya activity in 2018. Together, these records provide the only direct evidence of inter‐annual variability in the central Ross Ice Shelf cavity, and further reveal seasonally recurring intrusions of supercooled water that highlight a critical pathway by which ocean and climate variability can influence heat and freshwater redistribution beneath the ice shelf, with important implications for its stability.