Recently, Chuning Wang, assistant research professor at the School of Oceanography, Shanghai Jiao Tong University (SJTU-SOO), published a research paper titled “Quantification of Heat and Salt Budgets in the Western Ross Ice Shelf Cavity and Polynya System” in Geophysical Research Letters. The paper was completed by Chuning Wang (first author), Professor Zhaoru Zhang (corresponding author), and Professor Meng Zhou from SJTU-SOO.

The Antarctic Bottom Water (AABW) is a key water mass driving the lower limb of global meridional overturning circulation. Its precursor is the High Salinity Shelf Water (HSSW), which is mainly produced in the polynyas of the Southern Ocean marginal seas.

The Ross Sea is a major production region of HSSW, and the Ross Ice Shelf Polynya is one of its core production sites. Within the polynya, the physical properties of HSSW are jointly regulated by sea ice formation, ice shelf basal and edge melting, and subglacial discharge. However, due to the sparseness and seasonal biases of observational data, precisely estimating the water mass formation and transformation rates in the Ross ice shelf cavity–polynya system has long posed a major challenge.

In this study, a multi-platform integrated dataset spanning from 1980 to 2024 and covering the western Ross Sea was constructed (Fig. 1). With a box model (Fig. 2), we systematically estimated the heat and salt budgets of the Ross ice shelf cavity–polynya system. Three dominant processes were found to control the heat and salt budgets of the cavity: cavity–polynya exchange, glacial basal melting, and subglacial discharge. The box model yields a glacial basal melt rate of 54.3 Gt·yr⁻¹ (21.400 cm·yr⁻¹), consistent with previous studies; the estimated subglacial discharge rate is 87.0 Gt·yr⁻¹, substantially higher than previous estimates from subglacial hydrology models. These results indicate that the role of subglacial discharge in the evolution of water masses in Antarctic marginal seas has been significantly underestimated, providing an important scientific basis for incorporating subglacial discharge processes into future climate models.

Figure 1. Summary of observational data in the western Ross Sea. (a) Monthly mean profiles of potential temperature, salinity, and buoyancy frequency; (b) –S scatter plots in the deep ice shelf cavity and polynya; (c) ensemble mean of –S properties in the deep parts of the ice shelf cavity and polynya.

Figure 2. Conceptual diagram of the box model. The arrows denote: cavity–polynya exchange (red), ice shelf basal and edge melting (blue), subglacial discharge (gray), vertical mixing (purple), surface fluxes (yellow), and system residual circulation (pink). The numbers in (a) and (b) represent the annual mean contribution of each process to the fluxes and the corresponding uncertainty ranges (in parentheses).

It is worth noting that the box model calculations show that the freshwater input from glacial melting and subglacial discharge effectively compensates the salt input from sea ice formation, keeping the net salinity export of the entire system close to zero. This finding indicates that HSSW production is not solely driven by local polynya thermo-/dynamic processes—shelf-scale changes in the salinity budget, including sea ice formation and the intrusion of modified Circumpolar Deep Water, also play a key role in balancing the negative salinity flux from glacial meltwater.

This study was jointly supported by the National Natural Science Foundation of China (Grant No. 42306249), the Shanghai Pilot Program for Basic Research of Shanghai Jiao Tong University (21TQ1400201), and Shanghai Frontiers Science Center of Polar Science (SCOPS).

Original link: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025GL121363

Contributed by Research Group of Prof. Meng Zhou