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Collaborative Research: Inert Gas and Methane Based Climate Records throughout the South Pole Deep Ice Core
Entry ID: USAP-1443710_1

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Gases trapped in ice cores have revealed astonishing things about the greenhouse gas composition of the past atmosphere, including the fact that carbon dioxide concentrations never rose above 300 parts per million during the last 800,000 years. This places today's concentration of 400 parts per million in stark contrast. Furthermore, these gas records show that natural sources of greenhouse ...

This award funds the construction of the gas chronology for the South Pole 1500m ice core, using measured inert gases (d15N and d40Ar–Nitrogen and Argon isotope ratios, respectively) and methane in combination with a next-generation firn densification model that treats the stochastic nature of air trapping and the role of impurities on densification. The project addresses fundamental gaps in scientific understanding that limit the accuracy of gas chronologies, specifically a poor knowledge of the controls on ice-core d15N and the possible role of layering and impurities in firn densification. These gaps will be addressed by studying the gas enclosure process in modern firn at the deep core site. The work will comprise the first-ever firn air pumping experiment that has tightly co-located measurements of firn structural properties on the core taken from the same borehole.

The project will test the hypothesis that the lock-in horizon as defined by firn air d15N, CO2, and methane is structurally controlled by impermeable layers, which are in turn created by high-impurity content horizons in which densification is enhanced. Thermal signals will be sought using the inert gas measurements, which improve the temperature record with benefits to the firn densification modeling. Neon, argon, and oxygen will be measured in firn air and a limited number of deep core samples to test whether glacial period layering was enhanced, which could explain low observed d15N in the last glacial period. Drawing on separate volcanic and methane synchronization to well-dated ice cores to create independent ice and gas tie points, independent empirical estimates of the gas age-ice age difference will be made to check the validity of the firn densification model-inert gas approach to calculating the gas age-ice age difference. These points will also be used to test whether the anomalously low d15N seen during the last glacial period in east Antarctic ice cores is due to deep air convection in the firn, or a missing impurity dependence in the firn densification models.

The increased physical understanding gained from these studies, combined with new high-precision measurements, will lead to improved accuracy of the gas chronology of the South Pole ice core, which will enhance the overall science return from this gas-oriented core. This will lead to clarification of timing of atmospheric gas variations and temperature, and aid in efforts to understand the biogeochemical feedbacks among trace gases. These feedbacks bear on the future response of the Earth System to anthropogenic forcing. Ozone-depleting substances will be measured in the South Pole ice core record, and a precise gas chronology will add value. Lastly, by seeking a better understanding of the physics of gas entrapment, the project aims to have an impact on ice-core science in general.

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Description: NSF Award Abstract
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Data Set Citation
Version: 1
Temporal Coverage
Start Date: 2015-09-01T00:00:00.000Z
Stop Date: 2018-08-31T23:59:59.999Z
Location Keywords
Not applicable
Ancillary Keywords
Data Set Progress
Data Center
United States Antarctic Program Data Center
Data Center URL: http://www.usap-dc.org/

Data Center Personnel
Name: Data Manager
Email: info at usap-dc.org
Contact Address:
Lamont-Doherty Earth Observatory
61 Route 9W
City: Palisades
Province or State: NY
Postal Code: 10964
Country: USA
Jeffrey P. Severinghaus
Email: jseveringhaus at ucsd.edu
Contact Address:
University of California-San Diego Scripps Inst of Oceanography
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Extended Metadata Properties
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Creation and Review Dates
DIF Creation Date: 2019-02-04
Last DIF Revision Date: 2019-12-12