Kenji Kawamura

Office: 215 Vaughan Hall

Phone: 858.822.1642

Fax: 858.822.3310

Email: kkawamura@ucsd.edu

Vita (PDF)

Publications

Current Research Projects

(1) Argon, krypton and xenon as measures of deep convection in firn at Megadunes, Antarctica

Ice cores contain a wealth of information about past climate in air bubbles. Abrupt climate change is recorded in nitrogen and argon gas, which shows that Greenland abruptly warmed more than 10 degrees C at the onsets of Dansgaard-Oeschger events. However, air convection in the snow (firn) can reduce the gas signal, and it remains unknown to what extent the nitrogen-argon thermometer underestimates the magnitude of past abrupt climate change.

The age difference between ice and occluded air must be estimated by densification models, in order to establish phasing between atmospheric greenhouse gas variations and climate change, or between climate changes in the North (represented by methane concentration) and South (represented by ice isotopes) using Antarctic long ice cores (Vostok, Dome Fuji, Dome C). One way to check the validity of the models is to compare the firn thickness estimated by the models with that based on measured gravitational fractionation recorded in nitrogen or argon isotopes. However, the comparison is prone to a large uncertainty because air convection in the firn can reduce the gravitational signal. It remains unknown if the apparent discrepancy of up to 40 m in glacial periods is due to an extended convective zone.

Therefore, we need to know the size of past convective zones. We are studying deep convection at an Antarctic site called Megadunes. Here the heavy noble gases krypton and xenon reveal convection, because heavy gases diffuse slowly. Our new xenon-krypton technique promises to quantify past convection in ice core records, improving understanding of abrupt warmings and phasing between climate and greenhouse gases.

(2) Convective mixing of air in firn at four polar sites (collaboration with Tohoku University, Japan)
Firn air data at 4 polar sites (Dome Fuji, H72, and YM85, Antarctica and North GRIP, Greenland), sampled and measured by Japanese researchers including myself, are investigated to deduce the size of convective zone in the firn and its relationship with surface condition (e.g. porosity, accumulation rate and wind speed). An overall relationship between low accumulation rate and the presence of deep convective zone is suggested, with one notable exception that may be explained by strong wind forcing of air movement through the firn.

(3) Effect of Local Summer Insolation on O2/N2 and Total Air Content in the Dome Fuji Ice Core, Antarctica (collaboration with Tohoku University, Japan)
Air in polar ice cores has shown depleted O2/N2 ratios relative to the atmosphere. O2 molecules are preferentially excluded from freshly closed air bubbles at the base of the firn because O2 diffuses through the ice matrix faster than N2. The total air content (TAC) in ice core varies with temperature, atmospheric pressure and porosity at bubble close-off depth. We are investigating the data of O2/N2 ratio and total air content from the Dome Fuji ice core, Antarctica for the last 340,000 years, which were measured at Tohoku University for my PhD. The O2/N2 and TAC from the Dome Fuji core show a close resemblance with summer insolation at 77 °S. High TAC and high O2/N2 appear at times of low summer insolation. Both O2/N2 and TAC variations are too large to be explained by the atmospheric variations in the past. We propose a hypothesis that explains the link of insolation to both data sets, and use a firn gas diffusion and close-off model to evaluate it quantitatively.

(4) Diffusive separation of the lower atmosphere (collaboration with Dr. Ralph Keeling)
Nocturnal air in strong inversion layer at Borrego Desert was sampled to verify the possibility of thermal and gravitational fractionation of the natural atmosphere. We found the evidence of the diffusive fractionation in the troposphere.

Past Research Projects
March 2002 – July 2004
Postdoctoral Research Fellow at the division of Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland
Supervisor: Bernhard Stauffer
• Development of new dry extraction technique for measuring CO2 concentration in air occluded as clathrate-hydrates in deep ice cores.
• High-resolution CO2 reconstruction for the last 1000 yr from the EPICA Kohnen Station ice core, and for the Holocene and the penultimate glacial period from the Dome C ice core.
• High-resolution CH4 and N2O reconstruction for D/O events 9-12 from the North GRIP ice core, and for 44-220 kyr BP from the Dome C ice core.

April 2001 – February 2002
Postgraduate Research Student (and Research Assistant) at the Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, Japan
Supervisor: Takakiyo Nakazawa
• Analyses of the Dome Fuji ice core for CO2, δ13CO2 and N2O using a dry extraction method for the past 170,000 years.
• Firn air sampling at North GRIP, Greenland and their analyses for CO2, CH4 and N2O concentrations.
April 1996 - March 2001
Ph.D. in Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan.
Dissertation: "Variations of atmospheric components over the past 340,000 years from Dome Fuji deep ice core, Antarctica"
Supervisor: Takakiyo Nakazawa
• Analyses of the Dome Fuji ice core for CO2, CH4, N2O concentrations, δ15N of N2, δ18O of O2, O2/N2 ratio, and total gas content using a wet extraction method, for the past 340,000 years.
• Analyses of firn air sampled at Dome Fuji and H72, Antarctica, for CO2, CH4 and N2O concentrations, δ15N of N2, δ18O of O2, and O2/N2 ratio.

April 1994 - March 1996
M.Sc. in Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan.
Master’s thesis (in Japanese): "Study on molecular diffusion and gravitational separation of air components in firn"
Supervisor: Takakiyo Nakazawa
• Analyses of the H15 ice core for CO2, δ13CO2 and N2O with a dry extraction method, and δ15N of N2 and δ18O of O2 with a wet extraction method, for the past 250 years.