In 1691, writing within the transatlantic space of the colonial empire, Mexican author Carlos Sigüenza y Góngora uses his protagonist's adventures to explore the relationship between social recognition, law, and lawlessness as these concepts are represented in Los infortunios de Alonso Ramírez. After experiencing lawlessness at sea Alonso receives social recognition as a creole subject welcomed at the urban center of mainland Mexico by the viceroy of New Spain. Alonso's arrival in Mexico City and his immediate acceptance by the viceroy at the end of the narrative evidence a notable relationship between the law, social recognition, and geographic urban space.

The Antarctic Slope Current (ASC) is a narrow and westward circulation feature that surrounds the Antarctic continental shelves. It regulates onshore ocean heat transport toward the Antarctic ice shelves and dense water outflow, playing an important role in global meridional overturning circulation, glacier melt, and sea level rise. Despite its significance to Earth's climate system, the circulation and heat transport around the Antarctic margins remain poorly understood due to the difficulties and expense in observation and modeling.

In this work, the dynamics of the ASC and the ice-ocean interactions around the Antarctic margins are investigated using high-resolution process-oriented simulations. The key results are summarized as follows: (i) Due to topographic eddy suppression, almost no wind-input momentum is transferred vertically over the continental slope; as a result, sea ice horizontally redistributes the wind-input momentum away from the continental slope, playing a critical role in the momentum balance of the ASC. (ii) Melt-induced freshening of the coastal waters that are buoyant compared with the open ocean leads to increased eddy-driven shoreward heat flux, which implies a positive feedback in a warming climate that may cause further melt of ice shelves. (iii) The West Antarctic slope undercurrent originates from the cyclonic vorticity input by meltwater upwelling in the cavities of West Antarctic ice shelves, which drives warm Circumpolar Deep Water toward the glaciers; increased basal melt therefore strengthens the slope undercurrent and enhances onshore heat transport, which indicates another positive feedback that may accelerate future melt, potentially further destabilizing the West Antarctic Ice Sheet.

The work in this dissertation advances the understanding of the ice-ocean system near the Antarctic margins and highlights previously unrecognized climate feedbacks that may be key to projecting future changes in Antarctic ice sheets and thus sea level rise. In addition, our results help guide future climate model development and future observations of near-Antarctic ocean heat flux and glacier melt.

Background

Methods

Results

Conclusion

The circulation at the margins of Antarctica closes the meridional overturning circulation, ventilating the abyssal ocean with 0$_{2}$ and modulating deep CO$_{2}$ storage on millennial timescales. This circulation also mediates the melt rates of Antarctica’s floating ice shelves, and thereby exerts a strong influence on future global sea level rise. The near-Antarctic circulation has been hypothesized to respond sensitively to changes in the easterly winds that encircle the Antarctic coastline. In particular, the easterlies may be expected to weaken in response to the ongoing strengthening and poleward shifting of the mid-latitude westerlies, associated with a trend toward the positive index of the Southern Annular Mode (SAM). However, multi-decadal changes in the easterlies have not been systematically quantified, and previous studies have yielded limited insight into the oceanic response to such changes.

In this work we first quantify multi-decadal changes in wind forcing of the near-Antarctic ocean using a suite of reanalysis products that compare favorably with local meteorological measurements. Contrary to expectations, we find that the circumpolar-averaged easterly wind stress has not weakened over the past 3-4 decades, and if anything has slightly strengthened. However, there has been a substantial increase in the seasonality of the easterlies: our results suggest that in austral summer the intensification of the SAM has weakened the easterly winds, while during austral winter an intensification of Antarctica’s katabatic winds has strengthened the easterlies. These trends have wide-ranging implications for oceanic transport of heat to Antarctica’s floating glaciers, formation of dense waters on the continental shelf, and sea ice production and export.

To explore the impacts of Antarctica’ changing winds, we develop a comprehensive model of the southern Weddell Sea, including the Filchner-Ronne Ice Shelf (FRIS), Antarctica’s largest floating glacier. We investigate the wind-driven sensitivity of the circulation, dense water production, and glacial melt to idealized climate changes. We find that the circulation is relatively insensitive to changes in the zonal winds and atmospheric temperature, but strongly sensitive to changes in the meridional winds. Varying the strength of the meridional winds by a few tens of percent is sufficient to switch the FRIS cavity circulation between bi-stable ``warm’’ and ``cold’ states, accompanied by an order of magnitude change in the glacier’s melt rate. These findings imply that Antarctica’s major ice shelves may experience rapid changes in melt if certain climatic thresholds are exceeded, and that such changes would strongly inhibit a return to present-day melt rates. Alternatively, existing cold, dense water masses within the cavities might buffer against future intrusions of warm water and acceleration of Antarctic mass loss.