Gas group

History of temperature changes in Greenland

One of the best temperature proxies based entirely on physical processes is variations in nitrogen and argon isotopes in the entrapped air [Kobashi et al., 2015]. Snow falling on top of the Greenland ice sheet is transforming to ice under the weight of successive snowfalls. The fluffy snow structure is becoming an open porous sponge where the gas is finally occluded in small bubbles at about 70m below surface in Greenland. The atmospheric gas composition fractionates in this firn layer due to 1) gravitational settling combined with molecular diffusion and 2) thermal fractionation in the firn layer. Measuring molecules with a constant atmospheric ratio (e.g. nitrogen and argon), it is possible to separate the effects and to reconstruct past surface temperatures.

Our goal in this project is to make the isotope measurements continuously and in parallel to all other gas related measurements, e.g. methane, total air content, or nitrous oxide with the goal of high-resolution temperature reconstructions. The gas is extracted continuously from a melt stick from the EGRIP core. EGRIP is located in NE Greenland (75.63N, 35.99W) on the North East Greenland Ice Stream (NEGIS) the biggest ice stream in Greenland.



CO2 in the ancient atmosphere

From Rubino et al., 2013: (a) CO2 concentration (black circles) and the d13C (brown circles); solid lines are results of the double deconvolution for, respectively, (b) the atmosphere-terrestrial biosphere and (c) the atmosphere-ocean CO2 flux. Error bars are analytical uncertainties and dashed lines show the 1 sigma uncertainty associated to the Kalman filter double deconvolution.

Ice cores contain ancient air and the past atmosphere can be reconstructed from them. However, the past atmospheric composition of CO2 turned out to be a challenge. In the measurements from ice cores uncertainties arise from in situ processes affecting both concentration and isotopic composition. These uncertainties are passed on to calculations on how the past carbon cycle has been affected. The figure from Rubino et al., 2013 shows the status. The only way to minimize the uncertainty is to measure CO2 and δ13C in different ice cores with different impurities. In the frame of collaborative ice core drilling projects in Antarctica, we have access to two new cores. The goal of the 1-year master project is to obtain reliable measurements of both CO2 and δ13C. The focus of the project is the last millennium and interpretation of the records will be in international collaboration.

We have a working system to measure concentration and isotopic composition of CO2 with an Isotope Mass Spectrometer extracted from ancient air trapped in the polar ice sheets. The system has not been used in a while (due to moving the lab) and it needs to be extensively tested and upgraded. The master project is available immediately.

Contact: Thomas Blunier, Tagensvej 16, Office 1.1.11 (blunier@nbi.ku.dk).


Abrupt climate change and the nitrogen cycle

Figure 1: Top δ18O of H2O, a temperature proxy. Bottom N2O concentration [Flückiger et al., 1999].

Nitrous oxide (N2O) is a prominent component of the global nitrogen cycle and an important and strong greenhouse gas in the atmosphere; it is part of a feed-back loop with climate. Most N2O is produced by microbes during nitrification and denitrification in the terrestrial and oceanic realm. The combination of δ18O and δ15N discriminates between oceanic and terrestrial sources while the position dependent 15N in N=N=O distinguishes between nitrification and denitrification sources.

The greenhouse gas N2O has various biological origins distinguishable by their isotopic fingerprint. At times of abrupt climate change, like at the transition from the glacial to the present warm period (Figure 1) nitrous oxide concentrations rise most probably resulting from increased source emissions. We want to investigate which sources are responsible for the change and hope to get insight into how the biosphere is likely to respond to future climate change. This may provide information on whether these gases produce a positive or a negative feedback to the ongoing man-made climate change.

In this 1 year master project the student needs to build an extraction system and connect it to the laser spectrometer. The first step is to measure N2O and isotopomers from atmospheric air samples. The project could involve two students.

Contact: Thomas Blunier, Tagensvej 16, Office 1.1.11 (blunier@nbi.ku.dk).


High resolution greenhouse gas and temperature reconstruction from ice cores

Sketch of the current Copenhagen gas measurement system.

We pioneered methane measurements from a continuous melt stick in 2012 (Stowasser et al.) We are in the process of expanding our pallet of measurements including other trace gases and temperature reconstructions from isotopes in gases. We want to learn what is the exact timing of changes in the greenhouse gases methane and nitrous oxide relative to the temperature changes. The 1 year project involves system development, testing, measurement campaign and interpretation of the climate record.

Contact: Thomas Blunier, Tagensvej 16, Office 1.1.11 (blunier@nbi.ku.dk).

Stowasser, C., C. Buizert, V. Gkinis, J. Chappellaz, S. Schupbach, M. Bigler, X. Fain, P. Sperlich, M. Baumgartner, A. Schilt, and T. Blunier (2012), Continuous measurements of methane mixing ratios from ice cores, Atmospheric Measurement Techniques, 5(5), 999-1013, 10.5194/amt-5-999-2012.


Atmospheric Hydrogen as a new climatic parameter

We know much about the past atmosphere; E.g. the pace at which greenhouse gas concentrations have varied in the past. Our knowledge stems from the air trapped in ice cores. Interwoven with CH4 and CO are production and destruction processes of molecular hydrogen. Hydrogen thus offers complementary information on important components of the chemistry in our atmosphere. To our knowledge neither concentration nor isotope records of molecular hydrogen exist prior to 1993 (2). Our final goal is to extend this record based on ice core measurements. However, several aspects of such an endeavor are unclear. 1) Due to the small molecule size of H2 it is expected that hydrogen is lost after recovery of the ice core. 2) Hydrogen may fractionate during the last step of air occlusion in the ice. Both aspects need clarification.

The master thesis has two aspects 1) Measure the permeability of molecular hydrogen through natural ice. 2) Investigate the potential fractionation during air occlusion in polar firn. For the measurement a system needs to be designed and built.

Our current deep drill project EGRIP (https://eastgrip.org/) offers access to freshly drilled core to investigate above mentioned questions.

Contact: Thomas Blunier, Tagensvej 16, Office 1.1.11 (blunier@nbi.ku.dk).

References
1. Yver CE, et al. (2011) A new estimation of the recent tropospheric molecular hydrogen budget using atmospheric observations and variational inversion. Atmos. Chem. Phys. 11(7):3375-3392.
2. Prinn RG, et al. (2000) A history of chemically and radiatively important gases in air deduced from ALE/GAGE/AGAGE. Journal of Geophysical Research: Atmospheres 105(D14):17751-17792.


Modelling the termination of the last Ice Age in Greenland with the Community Firn Model

Are you looking for an exciting Msc thesis project where you can combine your Python computational skills with inverse methods and state of the art datasets of N2 and Ar isotopes in order to look far back in Greenland's past climate? If you are fascinated by polar research and curious about climate change processes this may be a unique chance for you to join a dynamic group with decades of history in polar and ice core research.
You will be looking into the abrupt warming signals during the sudden end of the last Ice Age about 12,000 ago and using a state-of-the-art model of snow densification and gas diffusion you will work towards quantifying the magnitude and rapidity of the abrupt climate change during this time. We require that you are familiar with Python and you can expect your skills to get very sharp during the duration of the project. You will get hands-on experience with polar snow/firn modelling tools and high quality datasets of N2 and Ar isotopes from the air bubbles in the ancient ice. We are a very open and dynamic group with a variety of nationalities and backgrounds as well as a wide international network of collaborations.

Should you have any questions on the project feel free to contact: Vasileios Gkinis and Michael Döring