Diatoms in Antarctic ice cores, a novel proxy for reconstructing past wind variability in the Pacific sector of the Southern Hemisphere Westerly Wind belt

Abstract

The Southern Hemisphere Westerly Winds play a critical role in the global climate system by modulating the upwelling and the transfer of heat and carbon between the atmosphere and the ocean. Since observations started, the core of the westerly wind belt has increased in strength and has contracted towards Antarctica. It has been proposed that these deviations are among the main drivers of the observed widespread warming in West Antarctica, threatening the stability of ice shelves, and ultimately contributing to global sea level rise.

Over the last decades, it has been widely believed these atmospheric changes have occurred in response to recently increased greenhouse gas (GHG) concentrations and ozone depletion. However, the lack of long-term wind records in the Southern Hemisphere mid-latitudes hinders our ability to assess the wider context of the recently observed changes. This lack of a clear consistent timing limits our understanding of the causes of westerly wind changes and the roles they have played in driving recent environmental changes in Antarctica. Addressing these questions is crucial for future climate predictions. The answer to this conundrum could be found in diatoms preserved in Antarctic ice core layers.

This project presents a thorough analysis of diatoms preserved in Antarctic ice to reconstruct past changes in the westerly wind belt and assess the role of winds in the changing Antarctic environment. A new method to extract and analyse these microscopic organisms preserved in ancient ice is designed, implemented, tested and validated. The spatial and temporal variability of the diatom record preserved in Antarctic ice is explored in 5 locations in the southern Antarctic Peninsula and Ellsworth Land. The regional study of these records reveal a direct link between changes in the intensity of westerly winds and the presence of diatoms in ice. This, therefore, presents a novel ice core wind proxy based on the abundance and diversity of diatoms preserved in ice cores. This novel proxy development enabled the reconstruction of wind variation over the last 140 years. This reconstruction provides first evidence to differentiate between past strengthening and/or migration of the westerly wind belt, a key component to understanding recent environmental changes in West Antarctica.

Results from this project reveal the recent poleward intensification of the wind belt is unprecedented in the last 140 years and synchronous with the increase of greenhouse gases and ozone depletion in the atmosphere. In turn, these results imply that recent changes in winds have acted as the lynchpin linking variations in atmospheric GHG and stratospheric ozone concentrations to environmental changes in West Antarctica.