Climate Research Simplified

In summary, the results provide the first characterization of late Holocene dust provenance in the Siple Dome ice core, located at the boundary of the Ross Sea embayment and continental West
Antarctica. The data exclude Australia and New Zealand as dust sources. Instead, we find that Patagonia is the only potential midlatitude dust source supplying Siple Dome, plus strong evidence that Antarctic ice-free areas supply about half of the dust reaching Siple Dome and West Antarctica; however, this does not include the Dry Valleys and the Transantarctic Mountains as a major source.

Acetylene is an atmospheric trace gas produced by combustion of fossil fuels, agricultural and domestic burning, and wildfires. In the preindustrial atmosphere, the major source of acetylene is from wildfires. We measured the abundance of acetylene in the air bubbles trapped inside polar ice cores from Greenland and Antarctica over the last 2,000 years for the first time. Variations in the atmospheric abundance of acetylene over Antarctica indicate large changes in preindustrial wildfire emissions. Using a model, we find that preindustrial wildfire emissions of acetylene during the Medieval Period (1000–1500 CE) could have been several fold greater than what is observed today. Acetylene emissions declined by about 50% at the onset of the Little Ice Age (1650–1750 CE).

Sea ice variability has a dramatic effect on regional and global climate. Because sea ice extent has such a large summer to winter difference, seasonally specific records of past sea ice conditions are necessary to properly interpret sea ice/climate relationships. Here we present a sea salt record from the South Pole Ice Core, which represents Southern Hemisphere sea ice changes during the last 11,400 years. We use an atmospheric chemistry model to show that wintertime sea salt in the South Pole Ice Core comes mostly from salty snow originating from sea ice. Wintertime sea ice variations are responsible for most of the long-term variability in the South Pole sea salt record. Ice core data across Antarctica show increasing sea salt concentrations since 11,400 years ago, representing cooling and sea ice expansion, particularly between 8,000-10,000 years ago. Between 5,000 and 6,000 years ago, a drop in sea salt indicates an abrupt reduction in sea ice cover in the South Atlantic. Interestingly, paleoclimate data suggest that sea ice was more extensive in the North Atlantic at this time, indicating a linked and opposing sea ice signal in the North and South Atlantic most likely due to changing ocean circulation.

The SP19 gas chronology for the SPC14 ice core covers the last 52 586 years, complementing the ice chronology presented in Winski et al. (2019). The gas chronology was created using over 2000 high-resolution, discrete CH4 measurements completed at Oregon State University and Pennsylvania State University. The resulting CH4 record was tied to the high-resolution CH4 record of the WAIS Divide ice core using the WD14 chronology. Abrupt changes in CH4 at D-O events as well as distinct variations of 20–30 ppb during the Holocene are used as tie points. The absolute uncertainty of the gas chronology changes through time to a maximum of ±540 years at 35 ka and an uncertainty of ±502 years at the bottom of the core. Key outcomes of this study include a gas age timescale for the SPC14 ice core, the observation of minimal smoothing of the gas record despite the exceptionally deep firn column at the South Pole, an empirical Δage record that can be used to test firn densification models, and the confirmation of centennial variability in atmospheric CH4.

An inverse method using a firn model with isotope diffusion provides self-consistent temperature, accumulation rate, and thinning histories. Glacial-interglacial temperature change at the South Pole was 6.7 ± 1.0 K. The δ18O/T sensitivity is 0.99 ± 0.03 permille/K. Reconstruction of ice thinning shows millennial-scale variations in thinning function and decreased thinning at depth compared to 1-D model.

The particles found in the SPICEcore are rhyolitic with ~75 wt.% SiO2, ~3 wt.% Na2O and K2O, and ~2 wt.% FeO. All individual point measurements were averaged after normalization of data from both analyses. In previous ice core cryptotephra work studies, a 2% uncertainty for SEM-EDS analyses was established and observed standard deviation of a secondary standard rhyolite glass fit within this parameterization.

The investigation of three ice cores in the margin of Jarvis Glacier, two of which reached the bed, reveals that microstructural properties are more consistent within cores than between cores. Grain shape, grain size, bubble aspect ratio and crystallographic fabric all vary with proximity to the lateral margin. Grains are less circular and larger, and bubbles are more elongate nearer the margin. The c-axes closer to the margin are slightly more concentrated and fewer are steeply inclined. The relationship between microstructural features and rheology remains insufficiently known to establish outside uncertainty whether the observed differences in grain size, grain shape and crystallographic orientation are sufficient to account for the increased strain at JE compared to JA. The other leading factor driving increased strain is stress concentrations near the margin, which we are not able to evaluate at the present time. The study site has abundant englacial water, mean temperatures warmer than −2°C, and lies less than a kilometer from the source, all factors that impede fabric development. The fact that a measurable fabric developed in Jarvis Glacier, where conditions are unfavorable, suggests that many shear margins will develop a rheologically significant crystallographic orientation fabric.

It has been widely thought that East Antarctica was ∼9°C cooler during the Last Glacial Maximum, close to the ∼10°C difference between then and now determined independently for West Antarctica. Buizert et al. used borehole thermometry, firn density reconstructions, and climate modeling to show that the temperature in East Antarctica was actually only ∼4° to 7°C cooler during the Last Glacial Maximum. This result has important consequences for our understanding of Antarctic climate, polar amplification, and global climate change.

A complete record of large volcanic eruptions during the last 11,000 years has been produced from a detailed chemical analysis of a 3,400-m long ice core from Antarctica. The record is a chronological list of 426 explosive volcanic eruptions with the quantity of emitted volcanic materials that can impact the global climate. A number of very large eruptions some 8,200 years ago may have triggered and/or enhanced an abrupt cold episode in Earth’s climate history. This record does not provide conclusive evidence that the Thera eruption occurred in the 17th century BCE.

ICECReW is a professional development workshop sponsored by IDP for early-career researchers. The workshop was conceived by members of the IDP Ice Core Working Group. Participants met with established researchers to better understand outcomes of and resources available from past ice core projects, learned about opportunities to engage with future efforts, and connected with potential collaborators. Participants also worked together before, during, and after the workshop to develop two synthesis papers.