Our main research interests involve greenhouse gas, permafrost and nitrogenous aerosols, which are very important to understand climate change and air quality. I pursue those interests through the study of trace gases in paleoatmospheric air preserved in ice cores and ice wedges in permafrost, and aerosols in modern air. Particular interests are greenhouse gases such as CO2, CH4, N2O and nitrogenous aerosols. They give invaluable information about how the greenhouse gases are controlled and how we can estimate budget of air pollutant. The understanding of the earth system that they provide will be extremely important for prediction of changes in future climate and the earth system.
1. Constructing High-resolution CO2 Records in Ice Cores: Carbon Cycles and Climate
We are particularly interested in how the carbon cycle behaves under variable climate conditions. I plan to make decadal- to millennial- timescale measurements of atmospheric CO₂ in samples from different time periods. Several questions may be addressed: for example, (1) when did CO2 change relative to the abrupt climate changes (e.g, abrupt warming or cooling events recorded in Greenland ice cores), (2) what controlled atmospheric CO2 in different age intervals and on different time scales, and (3) what was CO2 level before 800 ka, which is the oldest age for CO2 records from ice cores. Especially, the last question may be answered with a newly planned Dome A core, which may provide ancient air older than 1 million years.
2. Constructing High-precision CH4 and N2O Records in Ice Cores: Biogeochemical Cylcles and Climate Mechanisms
CH4 and N2O are not only important greenhouse gases, but they are also important for understanding paleoenvironments because CH4 is primarily controlled by terrestrial processes and N2O by both terrestrial and marine processes. For example, existing CH4 records track northern hemispheric climate recorded in Greenland ice cores and hydrological cycles as shown in speleothem records from caves in midlatitudes.
So far, a different analytical procedure has been used to obtain high-precision records for each gas species. Simultaneous measurements would speed up data acquisition and allow high-temporal resolution studies. For this purpose, our initial plan is to do dry extraction (no ice melting) because it will allow CO2 analysis. However, metal-to-metal friction should be avoided to reduce contamination of CH4, requiring modification of the device we most recently designed for CO2. Extracted gases will be analyzed with gas chromatographic methods using two or three detecting systems such as FID (Flame Ionization Detector) for CO2 and CH4 and ECD (Electron Capture Detector) for N2O.
3. 13C of CO2, site-specific isotopomers of N2O in ice cores
We would like to develop a new technique for 13CO2 study. 13C and 12C are stable isotopes and can be used to better characterize the global carbon cycles. For example, the sources and sinks of CO2 including the major carbon reservoirs produce isotopically distinct 13C/12C ratios of CO2. Therefore, comparison of the isotope ratios with the atmospheric inventory can yield constraints for the global budgets. Currently, only a few carbon isotopic studies have been done and the data precision and time resolution remain inconclusive in answering most of climatic questions. For example, how did ocean and terrestrial biosphere affect on atmospheric CO2 concentration during the last glacial period and Little Ice Age.
The site-specific N isotopomers of N2O may help us better constrain sources and sinks. We are developing measurement techniques with a Finnigan Delta-V isotope ratio mass spectrometer.
4. The nitrate isotopes (δ15N and δ18O - NO3-) of particulate matter (PM2.5) in South Korea
Due to the rapid economic growth of China, ultrafine dust (also known as PM2.5) that has been continuously generated has entered the Korean peninsula and has had a great impact on air quality of South Korea. Recently, high concentrations of haze exceeding the average concentration of PM2.5 (36-75 μg /m3) per day are increasing in the Korean peninsula, especially in metropolitan areas such as Seoul and Gyeonggi-do. Hence, research on the understanding of chemical properties as well as atmospheric reaction is urgently needed.
Nitrate (NO3-), the product of the oxidation of NOx gases, is the second highest compound among the ionic compositions of PM2.5 as forms of ammonium sulfate, ammonium nitrate and other harmful substances. To understand the chemical characteristics of the PM2.5 generation and causes in the Korean Peninsula, the atmospheric nitrates isotopes (δ15N and δ18O - NO3-) have been proposed as a useful tool for identifying NOx sources (coal combustions, vehicles, thermal power plants etc.) as the N atom between NOx sources and skinks are known to be conserved while the O atoms providing information on the oxidants of the photochemical reaction pathways involved in the conversion of NOx to NO3-.
Using a bacterial denitrifier method and NOAA’s HYSPLLT back trajectory model analysis, the isotopic characteristic (15N/14N and 18O/16O) of aerosol nitrate (NO3-) samples collected in South Korea can be analyzed. This may help us better understand how changes in NOx emission sources of different regions or within the local area will affect the isotopes in nitrate aerosols in South Korea.
5. Greenhouse gas formation in ground ice
Ground ice is one of the dominant components of permafrost soil and ranges in depth from a few millimeters to tens of meters. Our preliminary data for Alaskan soils collected during the frozen season show a vertical distribution of CH4 that is positively correlated with dominant genera of methanogenic bacteria, indicating that the CH4 produced during the winter was not transported to the surface. Thus, abrupt outgassing is expected when the active layer thaws the following spring and summer. The diffusion of greenhouse gases through an ice matrix is in an order of several centimeters for thousands of years (Ahn et al., 2009; Bereiter et al. 2009, 2014; Ikeda-Fukazawa et al. 2005). Thus, the ice layer should be an effective barrier for the diffusion of gas produced in permafrost soil. On the other hand, the ground ice may provide space for microbial greenhouse gas formation underground.
What are the geochemical controls on greenhouse gas production in ground ice? To better answer this question, the proposed work will focus on ice wedges in which gas bubbles occupy 3–5% of the total volume. Analysis of multiple greenhouse gases (CO2, CH4, and N2O) and other geochemical species in the ice wedge may help us understand the environments in which these gases were produced. Previous studies were conducted only to CO2 and CH4, and the formation processes are poorly constrained. Recently, our group applied dry gas extraction methods to Siberian ice wedges and observed inversely correlated relationships in plots of CO2 vs. CH4 and N2O vs. CH4
Figure 13. Greenhouse gas content in Siberian ice wedges. Anti-correlations are observed in the plots of CO2 vs. CH4 and N2O vs. CH4
6. δ37Cl in Polar Ice Cores: Chlorine Budget and Ozone Depletion?
This work could help us better understand the atmospheric chlorine budget and ozone depletion in polar regions. Stratospheric ozone is destroyed by atomic chlorine and bromine. The main source of the chlorine atom in the stratosphere originates from photodissociation of man-made chlorofluorocarbons (CFCs) and natural methyl chloride (CH3Cl). The latter comprises ~ 20% of stratospheric chlorine. Previous studies showed that δ37Cl of synthetic methyl chloride has a δ37Cl value of -6.8 ‰ ~ -6.0‰ while other man-made chlorine compounds show almost natural variability of -2 ~ +2 ‰ (Tanaka and Rye, 1991). If natural CH3Cl is also depleted in 37Cl, we could quantify the contribution of chlorine from natural CH3Cl (Tanaka and Rye, 1991). Based on collaboration with other isotope geochemists, I would like to investigate δ37Cl of ice cores from Antarctica to see if we can use the δ37Cl of ice in constraining stratospheric chlorine budget. The analytical methods may include thermal ionization of Cs2Cl+, which is suitable for the limited size of samples such as ice cores. Inductively Coupled Plasma Mass Spectroscopy can be also considered in case large amounts of ice are available.
1. Constructing High-resolution CO2 Records in Ice Cores: Carbon Cycles and Climate
We are particularly interested in how the carbon cycle behaves under variable climate conditions. I plan to make decadal- to millennial- timescale measurements of atmospheric CO₂ in samples from different time periods. Several questions may be addressed: for example, (1) when did CO2 change relative to the abrupt climate changes (e.g, abrupt warming or cooling events recorded in Greenland ice cores), (2) what controlled atmospheric CO2 in different age intervals and on different time scales, and (3) what was CO2 level before 800 ka, which is the oldest age for CO2 records from ice cores. Especially, the last question may be answered with a newly planned Dome A core, which may provide ancient air older than 1 million years.
2. Constructing High-precision CH4 and N2O Records in Ice Cores: Biogeochemical Cylcles and Climate Mechanisms
CH4 and N2O are not only important greenhouse gases, but they are also important for understanding paleoenvironments because CH4 is primarily controlled by terrestrial processes and N2O by both terrestrial and marine processes. For example, existing CH4 records track northern hemispheric climate recorded in Greenland ice cores and hydrological cycles as shown in speleothem records from caves in midlatitudes.
So far, a different analytical procedure has been used to obtain high-precision records for each gas species. Simultaneous measurements would speed up data acquisition and allow high-temporal resolution studies. For this purpose, our initial plan is to do dry extraction (no ice melting) because it will allow CO2 analysis. However, metal-to-metal friction should be avoided to reduce contamination of CH4, requiring modification of the device we most recently designed for CO2. Extracted gases will be analyzed with gas chromatographic methods using two or three detecting systems such as FID (Flame Ionization Detector) for CO2 and CH4 and ECD (Electron Capture Detector) for N2O.
3. 13C of CO2, site-specific isotopomers of N2O in ice cores
We would like to develop a new technique for 13CO2 study. 13C and 12C are stable isotopes and can be used to better characterize the global carbon cycles. For example, the sources and sinks of CO2 including the major carbon reservoirs produce isotopically distinct 13C/12C ratios of CO2. Therefore, comparison of the isotope ratios with the atmospheric inventory can yield constraints for the global budgets. Currently, only a few carbon isotopic studies have been done and the data precision and time resolution remain inconclusive in answering most of climatic questions. For example, how did ocean and terrestrial biosphere affect on atmospheric CO2 concentration during the last glacial period and Little Ice Age.
The site-specific N isotopomers of N2O may help us better constrain sources and sinks. We are developing measurement techniques with a Finnigan Delta-V isotope ratio mass spectrometer.
4. The nitrate isotopes (δ15N and δ18O - NO3-) of particulate matter (PM2.5) in South Korea
Due to the rapid economic growth of China, ultrafine dust (also known as PM2.5) that has been continuously generated has entered the Korean peninsula and has had a great impact on air quality of South Korea. Recently, high concentrations of haze exceeding the average concentration of PM2.5 (36-75 μg /m3) per day are increasing in the Korean peninsula, especially in metropolitan areas such as Seoul and Gyeonggi-do. Hence, research on the understanding of chemical properties as well as atmospheric reaction is urgently needed.
Nitrate (NO3-), the product of the oxidation of NOx gases, is the second highest compound among the ionic compositions of PM2.5 as forms of ammonium sulfate, ammonium nitrate and other harmful substances. To understand the chemical characteristics of the PM2.5 generation and causes in the Korean Peninsula, the atmospheric nitrates isotopes (δ15N and δ18O - NO3-) have been proposed as a useful tool for identifying NOx sources (coal combustions, vehicles, thermal power plants etc.) as the N atom between NOx sources and skinks are known to be conserved while the O atoms providing information on the oxidants of the photochemical reaction pathways involved in the conversion of NOx to NO3-.
Using a bacterial denitrifier method and NOAA’s HYSPLLT back trajectory model analysis, the isotopic characteristic (15N/14N and 18O/16O) of aerosol nitrate (NO3-) samples collected in South Korea can be analyzed. This may help us better understand how changes in NOx emission sources of different regions or within the local area will affect the isotopes in nitrate aerosols in South Korea.
5. Greenhouse gas formation in ground ice
Ground ice is one of the dominant components of permafrost soil and ranges in depth from a few millimeters to tens of meters. Our preliminary data for Alaskan soils collected during the frozen season show a vertical distribution of CH4 that is positively correlated with dominant genera of methanogenic bacteria, indicating that the CH4 produced during the winter was not transported to the surface. Thus, abrupt outgassing is expected when the active layer thaws the following spring and summer. The diffusion of greenhouse gases through an ice matrix is in an order of several centimeters for thousands of years (Ahn et al., 2009; Bereiter et al. 2009, 2014; Ikeda-Fukazawa et al. 2005). Thus, the ice layer should be an effective barrier for the diffusion of gas produced in permafrost soil. On the other hand, the ground ice may provide space for microbial greenhouse gas formation underground.
What are the geochemical controls on greenhouse gas production in ground ice? To better answer this question, the proposed work will focus on ice wedges in which gas bubbles occupy 3–5% of the total volume. Analysis of multiple greenhouse gases (CO2, CH4, and N2O) and other geochemical species in the ice wedge may help us understand the environments in which these gases were produced. Previous studies were conducted only to CO2 and CH4, and the formation processes are poorly constrained. Recently, our group applied dry gas extraction methods to Siberian ice wedges and observed inversely correlated relationships in plots of CO2 vs. CH4 and N2O vs. CH4
Figure 13. Greenhouse gas content in Siberian ice wedges. Anti-correlations are observed in the plots of CO2 vs. CH4 and N2O vs. CH4
6. δ37Cl in Polar Ice Cores: Chlorine Budget and Ozone Depletion?
This work could help us better understand the atmospheric chlorine budget and ozone depletion in polar regions. Stratospheric ozone is destroyed by atomic chlorine and bromine. The main source of the chlorine atom in the stratosphere originates from photodissociation of man-made chlorofluorocarbons (CFCs) and natural methyl chloride (CH3Cl). The latter comprises ~ 20% of stratospheric chlorine. Previous studies showed that δ37Cl of synthetic methyl chloride has a δ37Cl value of -6.8 ‰ ~ -6.0‰ while other man-made chlorine compounds show almost natural variability of -2 ~ +2 ‰ (Tanaka and Rye, 1991). If natural CH3Cl is also depleted in 37Cl, we could quantify the contribution of chlorine from natural CH3Cl (Tanaka and Rye, 1991). Based on collaboration with other isotope geochemists, I would like to investigate δ37Cl of ice cores from Antarctica to see if we can use the δ37Cl of ice in constraining stratospheric chlorine budget. The analytical methods may include thermal ionization of Cs2Cl+, which is suitable for the limited size of samples such as ice cores. Inductively Coupled Plasma Mass Spectroscopy can be also considered in case large amounts of ice are available.