Aurora Basin North, glacial isotopic composition data from the 2013-2014 season

Full description

The ABN1314_Glacial_isotopic_composition is the measured oxygen and deuterium isotopic data for the 'ABN' (Aurora Basin North) ice core (ABN1314) collected during the Antarctic 13/14 season. The glacial isotopic composition was measured on melted ice samples using a Picarro water isotope analyser (L2130-i). A key output for the ABN project will be the time series of water isotopes (d18O and dD), which provides a temperature proxy record. In addition, deuterium excess can be computed, to explore moisture source conditions, including its applicability as a source temperature. In addition, the time series of water isotopes (d18O and dD) will also contribute to the multi proxy approach for the chronological control of the ABN ice core.

An extra isotope spreadsheet was added to the dataset in June, 2020.

Over six weeks, between December 2013 and January 2014, 24 scientists in two field teams drilled a 303 m long ice core at the remote site. The goal was to fill a major gap in an array of 2,000 year ice core climate records distributed across Antarctica. Two smaller drills were used to recover two shallow ice cores 116 m and 103 m long spanning the past 800 to 1,000 years. Ancient air samples extracted from the boreholes, as well as from bubbles trapped in the ice cores, help us to examine changes in atmospheric composition over time. The Aurora Basin drill site is about 550 km from Australia’s Casey station.

Dr Mark Curran, from the Australian Antarctic Division, is the Science Leader for the project.

The ice cores will be used to measure a range of chemical constituents to reconstruct past climate.

The Aurora Basin team will use a field-based Picarro laser spectrometer to measure water (H2O) isotopes (different nuclear forms of oxygen and hydrogen) in the 400 m core. Ice formed under cooler conditions, for example, will contain more 16O while ice formed under warmer conditions will contain more of the heavier isotope, 18O. These isotope changes are mostly influenced by temperature, enabling scientists to infer what the temperature was when the snow originally fell. By measuring these isotopes on site, rather than in a laboratory on their return, the scientists will have a 2,000 year temperature record as soon as they leave the field.

Samples from the core will also be cut for later laboratory analysis of methanesulphonic acid (MSA). MSA is produced from the oxidation in the atmosphere of dimethylsulphide, which is itself produced by certain species of phytoplankton in the Southern Ocean. The amount of MSA in an ice core is related to the maximum extent of sea ice in the region — when there is more sea ice there is more phytoplankton activity following sea ice decay and therefore more MSA production.

One of the 120 m cores will be used purely for sulphur isotope analysis to assess the volcanic ‘forcing’ (impact) on natural climate variation over time. Similarly, carbon dioxide concentrations in the ice will be measured to assess the greenhouse gas forcing on natural climate variation while beryllium-10 measurements will give an indication of solar forcing.

Scientists from the Desert Research Institute in the United States will produce much of the fine detail climate record by measuring a range of chemical species and elements in the 400 m core. These include dust tracers such as magnesium and iron, ash from fires, seawater tracers such as sodium and bromine, and volcanic tracers such as copper and cadmium. These analyses will help date the ice core and provide information about natural aerosols and pollution levels in the recent era.

Finally, the team will extract air from the ‘firn’ ice at the top of one of the 120 m ice cores. Firn ice is unconsolidated ice that contains a lot of air space, unlike consolidated ice where air is trapped in bubbles. The extracted air will be ‘fresher’ or more modern than air trapped deep within the ice core and will provide a record of gas concentrations over recent decades (including carbon dioxide, carbon monoxide, methane, oxygen and nitrogen). This will help scientists better understand the carbon cycle and anthropogenic changes.

Aurora Basin is the ideal site for the research as it has sufficient snowfall of about 13 cm of ice per year; enough to provide the first record of year-to-year changes over the past 2000 years in this region of the continent.

Aurora Basin also harbours some of the deepest ice in Antarctica – over 3 km thick. Ice this thick could be over one million years old. Data collected during the drilling of the 2000 year ice core may help scientists locate a suitable site for drilling this million year old ice core.

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Progress Code: completed