Climate variability in coastal East Antarctica over the past millennia: insights from the Mount Brown South ice core water isotope record

Abstract

Antarctica and the Southern Ocean represent critical components of the global climate system. However, understanding the inter-annual to decadal-scale variability in Antarctica is limited by the short-observational window. In lieu of direct observations of climate in the Southern Hemisphere high latitudes, ice core records are used to augment the short observational records to constrain regional climate variability. In particular, ice core records from coastal or quasi-coastal regions, where high annual accumulation preserves annual layers, are critical for constraining the inter-annual to decadal-scale variability experienced over the last 2000 years. While some regions of Antarctica have a high density of available high-resolution ice core records, others are notable for the lack of record availability. In particular, the Southern Indian Ocean sector of East Antarctica is deficient in ice core records. This region overlies several subglacial basins which pose critical concern for future ice loss from the East Antarctic Ice Sheet, and yet little is known about the long-term variability within this region.

This thesis presents a new record from coastal East Antarctica, the 295-m Mount Brown South water isotope record. Stable water isotope records from ice cores are frequently interpreted as temperature proxies. While this is largely true, they also reflect changes in atmospheric circulation and associated changes in fractionation at a synoptic and regional scale. In this thesis, I investigate the relationship between the isotopic record from the Mount Brown South ice core and climate at a range of spatial and temporal scales.

The synoptic conditions during precipitation are over-represented within ice core records. This phenomenon is particularly pronounced at the Mount Brown South ice core site, where precipitation is related to incursions of marine air masses onto the ice sheet, guided by the unique orography of the Amery Ice Shelf. This results in a bias in the ice core towards recording the warm temperatures associated with these marine incursions but also allows for the preservation of larger-scale atmospheric conditions which persist during these events. The magnitude of the zonal wave 3 pattern in the Southern Hemisphere is associated with atmospheric blocking and increased meridional transport, allowing for incursions of moist maritime air masses to the Mount Brown South region. Enriched stable water isotope ratios in the Mount Brown South ice core record are associated with snowfall during periods of enhanced blocking and stronger meridional transport, resulting in Mount Brown South preserving a record of the zonal wave 3 pattern. The relationship between synoptic-scale weather and large-scale modes of climate variability differs regionally. The Mount Brown South ice core record is compared with the nearby Law Dome ice core record. Despite their proximity, the two records display markedly different isotope signals that can be explained by the regional relationships to large-scale atmospheric processes. The Mount Brown South record is influenced by local effects driven by strong meridional transport associated with atmospheric blocking and zonal wave 3 magnitude. In contrast, the Law Dome record represents regional climate variability driven by changes in the phase of the Southern Annular Mode.

The differing responses of individual records to large-scale drivers of atmospheric variability underpins the utility of proxy networks in reconstructing hemispheric-wide climate variability. Results from this thesis identify the imprint of strong meridional transport on the Mount Brown South water isotope record. This relationship is then expanded to incorporate the Mount Brown South record into a wider array of paleo-climate proxies to address larger questions that pertain to Antarctic climate variability associated with changes in the large-scale drivers of atmospheric variability. Show more