Atmospheric dust transport to high-elevation Dronning Maud Land, Antarctica, over the satellite era and implications for centennial scale ice core records of dust deposition

Deposition of aeolian mineral dust recorded in Antarctic ice cores is strongly tied to large-scale atmospheric circulation variability. This natural archive can be used to extend knowledge about atmospheric circulation variability in the Southern Hemisphere (SH) prior to the satellite era (1979-2017). Additionally, dust plays an important role in the climate system through cloud formation processes, the radiation budget, and as a micronutrient source for biological productivity in the Southern Ocean. Hence, investigating the drivers of Antarctic dust variability is useful for better understanding past and future changes to SH climate. This thesis investigates present-day dust transport to a high elevation ice core site in Dronning Maud Land (DML; 74°60′S, 0°6′E), Antarctica, where an anomalous increase in dust deposition is observed over the past century in a 1300-year ice core recently drilled as part of the Isotopic Constraints on Past Ozone Layer in Polar Ice (ISOL-ICE) program.

This study aims to determine the potential source area (PSA) and atmospheric transport mechanism of dust deposited to high-elevation DML over the satellite era. Additionally, the implications of the findings for ice core dust records spanning the last millennium are also discussed. The specific objectives of this study are: 1) identify dominant atmospheric dust transport pathways to DML over the satellite era, 2) determine regional climatic controls of particle size distribution (PSD) at DML over the satellite era, and 3) contextualise the recent increase in dust deposition at DML relative to the last millennium.

To achieve these three objectives, dust deposition to the ISOL-ICE ice core site over the satellite era is examined using dust dispersion modeling (Flexpart model; Pisso et al., 2019) and correlation analysis with a range of climate parameters, such as geopotential height, zonal and meridional winds, and precipitation, using the ERA-interim atmospheric reanalysis dataset (Dee et al., 2011). Flexpart is configured to run backward dust dispersion simulations to investigate dust transport pathways and potential source areas to the ISOL-ICE site constrained by PSD observations from the ISOL-ICE core. The correlation analysis determines which large-scale circulation/climate patterns are important for dust transport to ISOL-ICE site. Both methods help ascertain drivers of modern dust transport to the ISOL-ICE site, providing new insights into potential drivers of the observed dust variability before the satellite era.

Analysis of the ISOL-ICE dust record reveals an abrupt 10-fold increase in dust deposition relative to the past millennium that occurred over ~15 years from 1915 to 1930 CE. Dust flux increased from a background mean of 0.03 mg m-2 yr-1 (668-1915 CE) to 0.30 mg m-2 yr-1 (1915-2017). Similarly, the coarse particle percentage (CPP) of dust, a proxy for PSD, rose from a mean of 71 % before 1900s to 83 % after the abrupt shift in dust flux. This abrupt increase is not observed in other ice core dust records from the Antarctic Peninsula, West Antarctica, or coastal DML, suggesting that the observed increase is a regional and/or high-elevation signal rather than Antarctic-wide.

The ISOL-ICE ice core dust deposition is characterised by relatively low dust concentration and dust flux, fine particle size (a dust mode of ~3.5-3.8 μm) for long-range transported dust (1-10 μm), and a maximum seasonal deposition in winter/spring. These characteristics combined with back trajectory analysis point to long-range transport from remote southern South America (SSA) as the dominant PSA. Back trajectory modeling shows that dust is transported to the ISOL-ICE site dominantly from the eastern coast of SSA between 47-50°S, and that dust transport pathways from SSA to the ISOL-ICE site are insensitive to particle size and seasonality over the satellite era. Moreover, dust from SSA are uplifted to ~1500 meters above sea level (m.a.s.l.) over the SSA region and are transported with increasing altitude towards DML. While SSA is the dominant PSA for the ISOL-ICE site, additional inputs from nearby Antarctic dust sources cannot be ruled out based on the presence of large coarse particles (10-50 μm) and published geochemical evidence from nearby ice core sites in DML.

The observed interannual variability of dust CPP at the ISOL-ICE site over the satellite era is associated with cyclonic circulation south of SSA, further supporting long-range transport of dust from SSA to the ISOL-ICE site. This circulation pattern explains 9-36 % of the observed variability in CPP at the ISOL-ICE site and is associated with convective activity in the South Pacific Convergence Zone (SPCZ) and the central tropical Pacific. During winter and spring, dust is transported to the ISOL-ICE site through a deep and broad Amundsen Sea Low, coinciding with the observed seasonal maximum in dust deposition at the site. During summer and autumn, the proposed dust transport occurs through a cyclonic circulation over the Drake Passage that is tied to the Pacific Decadal Oscillation (PDO). Interestingly, the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) do not appear to be significant drivers of cyclonic activity south of SSA and consequent dust transport to the ISOL-ICE site contrary to published ice core studies from coastal DML and West Antarctica that implicate SAM and ENSO as important drivers of dust transport from SSA to Antarctica.

This study, combined with geochemical evidence from high-elevation DML over the last glacial and Holocene period, suggests that the present-day dominant PSA of South America did not change since the last glacial period. In addition, dust transport pathways and the seasonality of dust deposition also did not change over this period. These constant factors suggest that the abrupt increase in dust concentration over the last century could have resulted from either 1) an enhanced cyclonic circulation south of SSA related to the SPCZ and PDO or 2) changing conditions at the two PSA regions (SSA and dust input from nearby Antarctic dust sources). Stronger cyclonic activity south of SSA leads to enhanced wind flow and drier conditions over SSA allowing for increased dust transport from SSA to the ISOL-ICE site. Comparatively, changes in source conditions (e.g., aridity and soil sediment supply) in the PSA alter the availability and physical characteristics of emitted dust particles.

The established relationship between dust CPP and the cyclonic circulation south of SSA over the satellite era provides a foundation for future work to investigate the drivers of dust variability in the high-elevation DML region over the past millennium. Findings from this study are also useful for investigating episodic dust events within the satellite era and potentially predicting how dust transport patterns will evolve in the future based on projected changes to atmospheric circulation patterns.